To control and diagnose digital devices, two main groups of methods are used: test and functional. For their implementation, hardware and software are used. During test control, special effects (tests) are applied, and the reactions of the controlled system (device, node) are recorded and analyzed at a time when, as a rule, it does not work for its intended purpose. This determines the scope of this type of control: in the process of setting up systems, during the regulations, for autonomous testing of systems before the start of normal operation.

Functional control is intended for monitoring and diagnosing the system during its operation. However, if the means of functional control are available in the system, then they, as a rule, are also used in test control. Functional control means provide:

Detection of a malfunction at the moment of its first manifestation at a control point, which is especially important in the case when the action of the malfunction must be quickly blocked;

Issuance of information necessary to control the operation of the system in the presence of a malfunction, in particular, to change (reconfigure) the structure of the system;

Reduced troubleshooting time.

Using hardware functional control, redundant equipment is introduced into the structure of a node or device, which functions simultaneously with the main equipment. Signals arising during the operation of the main and control equipment are compared according to certain laws. As a result of such a comparison, information is generated on the correct functioning of the controlled node (device). In the simplest case, a copy of the checked node (the so-called structural redundancy) is used as redundant equipment, as well as the simplest control ratio in the form of a comparison of two identical sets of codes. In the general case, simpler control devices are used, but methods for obtaining control ratios become more complicated.

To control the functioning of the main and control devices, methods of comparison are used: input and output words, internal states and transitions.

The first method corresponds to duplication, majorization, as well as control by prohibited code combinations. It also includes methods of redundant coding. Redundant coding is based on the introduction of additional symbols into the input, processed and output information, which, together with the main ones, form codes that have error detection (correction) properties. The second method is mainly used to control digital control devices.

For control, the following types of codes have become widespread: a code with a parity check, a Hamming code, iterative codes, equilibrium codes, codes in residues, and cyclic codes.

Code with parity (odd) check is formed by adding to the group of information bits, which are a simple (not redundant) code, one redundant (control) bit. When using parity, the parity check digit is "0" if the number of ones in the code is even, and "1" if the number of ones is odd. In the future, during transmission, storage and processing, the word is transmitted with its category. If, during the transmission of information, the receiving device detects that the value of the check digit does not correspond to the parity of the sum of word units, then this is perceived as a sign of an error. For odd parity, the complete loss of information is controlled, since the code word consisting of zeros is forbidden. The parity-checked code has little redundancy and does not require much hardware to implement the parity check. This code is used to control: transfer / information between registers, reading information into random access memory, exchanges between devices.

Iterative codes are used to control the transfer of arrays of codes between an external memory and a processor, between two processors, and in other cases. An iterative code is formed by adding additional parity bits to each row to each column of the transmitted array of words (two-dimensional code). In addition, parity can also be determined by the diagonal elements of the word array (multidimensional code). The detectability of the code depends on the number of additional control characters. It allows you to detect multiple errors and is easy to implement.

Correlative codes are characterized by the introduction of additional characters for each bit of the information part of the word. If there is 0 in any bit of the word, then in the correlation code it is written as "01", if 1, then the symbol "10". A sign of code distortion is the appearance of the characters "00" and "11".

Simple repetition code(coincidence control) is based on the repetition of the original code combination, decoding occurs by comparing the first (information) and second (test) parts of the code. If these parts do not match, the accepted combination is considered erroneous.

Equilibrium codes are used to control data transfers between devices, as well as when transferring data over communication channels. An equilibrium code is a code that has some fixed number of units (weight is the number of units in the code). An example of an equilibrium code is the code "2" from "5", from "8". There is an infinite number of equilibrium codes.

Control on forbidden combinations, microprocessor devices use special circuits that detect the appearance of prohibited combinations, for example, access to a non-existent address, access to a non-existent device, incorrect address selection.

Hamming Correction Code is constructed in such a way that a certain number is added to the available information bits of the word D check bits that are formed before the transmission of information by calculating the parity of the sums of units for certain groups of information bits. The control device at the receiving end forms the error address from the received information and control bits by similar parity calculations, the erroneous bit is corrected automatically.

Cyclic codes used in the means of serial transmission of binary characters that make up a word. A typical example of such means is a communication channel through which discrete data is transmitted. The peculiarity of cyclic codes that determine their name is that if an N-digit code combination belongs to a given code, then the combination obtained by cyclic permutation of characters also belongs to this code. The main element of the coding and decoding equipment when working with such codes is a shift register with feedback, which has the necessary cyclic properties. The cyclic code of an N-digit number, like any systematic code, consists of information and control characters, the latter always occupying the least significant digits. Since the serial transmission is made from the most significant digit, the control characters are transmitted at the end of the code.

Software functional controls are used to improve the reliability of the operation of individual devices, systems and networks in the event that the effectiveness of hardware error detection is insufficient. Software methods of functional diagnostics are based on the establishment of certain relationships between the objects involved in the course of work to ensure error detection. Individual commands, algorithms, program modules, software complexes (functional and service) can act as objects.

Control ratios are set at the system, algorithmic, software and microprogram levels.

The formation of control states is based on two principles:

Implementation by software of various levels of functional diagnostic methods based on coding theory, i.e. information redundancy is used;

Compilation of special ratios for different rules based on the use of temporal redundancy (double and multiple counting, comparison with pre-calculated limits, algorithm truncation, etc.) by transforming the computational process.

Both principles are used to diagnose all the basic operations performed by processor means - input-output operations, storage and transmission of information, logical and arithmetic.

Dignity software tools functional control is the flexibility and the ability to use any combination for the rapid detection of errors. They play an important role in ensuring the required level of reliability of information processing. For their implementation, they require additional costs of computer time and memory, additional programming operations and preparation of control data.

Control by double or multiple counting consists in the fact that the solution of the entire problem as a whole or its individual parts is performed two or more times. The results are compared and their coincidence is considered a sign of fidelity. More complex comparison rules are also used, for example, majorized ones, when we take the result that corresponds to a larger number of correct results as the correct one.

The implementation of double or multiple counting consists in determining the control points at which the comparison will take place, and allocating special amounts of memory to store the results of intermediate and final calculations, applying commands for comparing and conditionally jumping to continue the calculation (if the results match) or to the next repetition (if the results do not match.).

Control by the truncated algorithm method, based on the analysis of the algorithms executed by the processor, the so-called truncated algorithm is constructed. The problem is solved both by the full algorithm, which provides the required accuracy, and by the truncated algorithm, which made it possible to quickly obtain a solution, albeit with less accuracy. Then the exact and approximate results are compared. An example of a truncated algorithm is changing the solution step (increase) when solving differential equations.

Substitution method. When solving systems of equations, including non-linear and transcendental ones, substitution of the found values ​​into the initial equations is provided. After that, the right and left parts of the equation are compared to determine the residuals. If the residuals do not go beyond the specified limits, the solution is considered correct. The time spent on such control is always less than on re-decision. In addition, in this way, detect not only random, but also systematic errors, which are often missed by double counting.

Limit test method or the "forks" method. In most problems, it is possible to find in advance the limits ("fork"), in which some of the required quantities must lie. This can be done, for example, on the basis of an approximate analysis of the processes described by this algorithm. The program provides for certain points where the check for finding variables within the specified limits is implemented. This method can detect gross errors that make it pointless to continue work.

Validation with additional links. In some cases, it is possible to use additional relationships between the sought values ​​for control. A typical example of such connections are the well-known trigonometric relations. It is possible to use correlations for the tasks of processing random processes, static processing. A variation of this approach are the so-called balance methods, their essence is that individual groups of data satisfy certain ratios. The method allows you to detect errors caused by failures.

Method of redundant variables consists in the introduction of additional variables, which are either connected by known relations with the main variables, or the values ​​of these variables under certain conditions are known in advance.

Countdown control, at the same time, according to the result obtained (function values), the initial data (arguments) are found and compared with the initially specified initial data. If they match (with a given accuracy), then the result is considered correct. Inverse functions are often used for counting backwards. The use of this method is expedient in cases where the implementation of inverse functions requires a small number of instructions, computer time and memory costs.

Checksum method. Separate arrays of code words (programs, initial data, etc.) are assigned redundant control words, which are obtained in advance by summing up all the words of this array. To implement the control, the summation of all the words of the array and a bitwise comparison with the reference word are carried out. For example, when transmitting data over a communication channel, all encoded words, numbers, and symbols of the transmitted group of records are summed at the input to obtain checksums. The checksum is recorded and transmitted along with the data.

Control by record counting method. The record is called exactly set set data characterizing some object or process. You can pre-calculate the number of records contained in individual arrays. This number is stored in memory. While processing the corresponding data set, the checksum is periodically checked to detect lost or unprocessed data.

Time control for problem solving and the frequency of output results, is one of the principles for determining the correctness of the computational process. An excessive increase in the duration of the solution indicates the "cycling" of the program. The same purpose is served by the so-called marker pulses (or time stamps) used in real-time systems. Marker pulses are used to prevent the processor from stalling or performing incorrect calculation cycles due to an error in the instruction sequence. They are used both for the entire algorithm and for individual sections.

The implementation of these methods consists in determining the longest command route, taking into account interruptions by other programs. As part of the processor, a program time counter is used, on which the maximum allowable time for program implementation is set. When the counter reaches zero, a signal for exceeding the allowable control time is generated, which ensures the interruption of the program. Control of the sequence of execution of commands and software modules carried out in two ways. The program is divided into sections, and a convolution is calculated for each section (by counting the number of operators, by the method of signature analysis, by using codes). Then the trace of the program is taken and the convolution is calculated for it and compared with the pre-calculated one. Another way is that each section is assigned a specific code word (site key). This key is written to the selected RAM cell before the start of the section execution, one of the last commands of the section checks for the presence of "its" key. If the code word does not match the section, then there is an error. The nodes of branching programs are verified by repeated counting, and the choice of only one branch is checked using keys. The control of cyclic sections of the program consists in checking the number of repetitions of the cycle, due to the organization of an additional program counter.

At test control the check of nodes, devices and the system as a whole is carried out with the help of special equipment - generators of test effects and analyzers of output reactions. The need for additional equipment and time costs (the impossibility of regular (functioning during the test) limits the use of test methods.

Testing with a regular program, the functional diagram of the organization of such testing includes a test generator containing a set of pre-prepared statistical tests and an analyzer that works on the principle of comparing the output reaction with the reference one, also obtained in advance by special test preparation tools.

At probabilistic testing as a test generator, a generator of pseudo-random effects is used, implemented, for example, by a shift register with feedback. The analyzer processes the output reactions according to certain rules (determines the mathematical creation of the number of signals) and compares the obtained values ​​with the reference ones. Reference values ​​are calculated or obtained on a previously debugged and tested device.

contact testing(comparison with the standard) lies in the fact that the method of stimulation can be any (software, from the generator of pseudo-random effects), and the reference reactions are formed in the process of testing using a duplicating device (standard). The analyzer compares the output and reference responses.

Syndromic testing(method of counting the number of switching). The functional circuit contains a test generator that generates a count of 2N sets at the input of the circuit, and at the output there is a counter that counts the number of switching, if the number of switching is not equal to the reference value, then the circuit is considered faulty.

At signature testing output reactions obtained for a fixed time interval are processed on a shift register with feedback - a signature analyzer that allows you to compress long sequences into short codes (signatures). The signatures obtained in this way are compared with the reference ones, which are obtained by calculation, or on a pre-debugged device. Stimulation of the control object is carried out using a generator of pseudo-random effects.

In conclusion, it should be noted that there is no universal control method. The choice of method should be made depending on the functional purpose of the digital device, the structural organization of the system, the required indicators of reliability and reliability.

When conducting maintenance work or during the pre-flight preparation of the CPI, the main methods of control are test methods. During the flight, functional control methods are the main ones, and testing is mainly carried out in order to localize faults, if they occur.

6. PREDICTION OF THE STATE OF MEASURING AND COMPUTING COMPLEXES, ACCORDING TO THE INFLUENCE

ELASTIC PROPERTIES ON THE OBJECT OF CONTROL

What is Technical Diagnostics What does the System include technical diagnostics What tasks of monitoring and diagnostics are solved at the development stage What is a diagnostic parameter sign How are technical diagnostic systems divided according to the degree of coverage How are technical diagnostic systems subdivided according to the nature of interaction between STD and technical diagnostic tools

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Lecture 2

Subject.

Target. Give the concept of methods of technical diagnostics for electronic systems.

Educational. Explain the concepts of diagnostic methods.

Developing. Develop logical thinking and natural - scientific worldview.

Educational . Raise interest in scientific achievements and discoveries in the telecommunications industry.

Interdisciplinary connections:

Providing: computer science, mathematics, computer engineering and MT, programming systems.

Provided: Internship

Methodological support and equipment:

Methodological development for the lesson.

Syllabus.

Training program

Working programm.

Safety briefing.

Technical teaching aids: personal computer.

Providing jobs:

• Workbooks

Lecture progress.

Organizing time.

Analysis and verification of homework

Answer the questions:

1. What directions characterize the structure of technical diagnostics? Give a definition to each of them.
2. Explain the definitionRecognition of the state of the system",what determines the number of diagnoses?
3. What properties should the parameters describing the state of the system have?
4. What is Technical Diagnostics?
5. What is maintenance?
6. What is meant by equipment repair?
7. What's happened Maintainability?
8. What types of repair of digital systems are provided? Give a definition to each of them.
9. Explain the definition of "technical condition".
10. What are the types of object states? Describe each of them.
11. Explain termsCorrect functioning and Incorrect functioning.
12. What's happened Technical diagnostics?
13. What does it includeSystem of technical diagnostics?
14. What tasks control and diagnostics are solved at the development stage?
15. What is a diagnostic parameter (sign)?
16. How are the systems of technical diagnostics divided according to the degree of coverage?
17. How are technical diagnostic systems subdivided according to the nature of the interaction of STD with technical diagnostic tools (SrTD)?

Lecture plan

METHODS OF CONTROL AND DIAGNOSIS OF DIGITAL SYSTEMS

1.1 Features of modern digital systems as an object of control and diagnostics

1.2 Analysis of fault models of digital devices

1.3 Types and methods of control and diagnostics

1.4 Built-in control of digital systems

1.5 Features of modern digital systems as an object of control and diagnostics

The advent of microprocessor-based digital systems, in combination with specialized LSI, VLSI and IPC, has led to a serious problem in providing efficient service in their places of operation. Most specialists involved in the maintenance of complex digital systems have quite clearly realized that the problem of monitoring and diagnostics under operating conditions cannot be treated as a matter of secondary importance. Therefore, improving the technical and operational characteristics of complex digital systems based on LSI, VLSI and MPC is inextricably linked with the development of new methods and diagnostic tools with the need for comprehensive accounting and analysis of digital boards and their components as an object of control and diagnostics.

Features of control and diagnostics of digital boards with LSI and VLSI are characterized by the following :

- a wide range of LSI and VLSI characteristics;

The number of control tests, which can reach several thousand;

Digital boards with LSI and VLSI have a trunk principleorganization, which requires data exchange on 4, 8, 16 -bit tires in one period clock frequency, andsimultaneous multi-channel control;

- trunk buses in most LSI and VLSI havebidirectional mode of operation, so the control equipment must be able to switch from transmit to receive within one clock period;

Digital boards with LSI and VLSI can have in interface circuitsseveral bidirectional I/O channels;

Since temporal characteristics play an important role, the operationscontrol should be performed at a frequency close to the operating frequency up to 10 20 MHz.

Microprocessor systems (MPS) also have a number of features that do not allow the use of traditional equipment:

- description of circuits is difficult, since their functions, in M PS implemented firmware stored in ROM. The operation of these circuits is hidden inprogram algorithm;

Similar difficulties arise in connection with the dynamism of work M PS, in which impulse signals usually operate fora few microseconds and then disappear.

Parallel structure of buses to which several are connected at oncedevices in an OR scheme makes it difficult to find the source malfunctions.

Therefore, you need to knowonly where to look, but also when to look;

Thus, we can point out the general features of digital boards based on LSI, VLSI and MPC, which determine the complexity of their control:

Increased complexity of the control object;

Limited access to controlled nodes;

Tire organization;

The need for real-time control;

Microprogram management MP;

Incomplete control of LSI and VLSI components;

- influence on the stability of the functioning of the MPS input

conductivities of LSI, VLSI and structural elements;

The high cost of detecting and eliminating defects, etc.

Based on the foregoing, it can be noted that in the operating conditions of digital systems, it is required to solve the following problems of monitoring and diagnostics:

1 . Reducing the cost of control and diagnostic work in order to minimize the cost of repair and restoration work.

2. Collection and processing of information on operational reliabilitydigital boards and their components, as well as temporary andeconomic costs for troubleshooting.

In order to develop an automated device for diagnosing digital boards (ADDC) and create a diagnostic database, the following should be developed:

- methodology for analyzing the range and technical data of specified types of digital boards as an object of control and diagnostics for tools

Diagnostics based on the method of signature analysis;

Technique for the analysis of statistical data of controlled operation of digital systems to determine the reliability characteristics of digital boards.

In the first directionit is necessary to analyze the range and technical data of digital boards and their components, which includes:

1 . Distribution of the number of different by functional purposedigital boards in a digital system;

2. The number of types of digital boards and their sizes: types, series andthe number of ICs, LSI, VLSI and IPC;

3. Types and number of connectors, number of connector pins in different types digital boards;

4. Operating frequencies of the functioning of the nodes in the considered digital boards;

5. Voltage gradation of power supplies for various digitalboards with IC, LSI, VLSI and IPC.

In the second direction, it is necessary to analyze the existing subsystem of repair and restoration work (RVR) associated with digital boards:

1 . General organization, methods and means of control and diagnostics,used in RVR;

2. Time and cost costs for the controldiagnostic operations for given digital boards and repairrestoration work (RVR) in general;

3. Analysis of the reliability characteristics of digital boards and their components based on the results of generalized operating experience.

It is necessary to analyze:

A ) failure rate of digital boards;

b) the proportion of failures of individual digital boards in the total number of equipment failures;

c) average troubleshooting time;

d) MTBF and mean recovery time of digital boards;

e) ranking of digital boards according to the criterion of operational reliability.

Thus, the AUDC diagnostic database being created provides for the storage of:

Information about the types of ICs, LSI, VLSI and IPC and their reference signatures required when replacing them and for organizing input control;

Information about the tested digital boards and their reference signatures directly on the pins of the connectors;

Information about the topological model of the circuit of digital boards;

Algorithms for finding and localizing the fault location in digital boards;

Information about external docking parameters required when setting up and testing the performance of restored digital boards and bringing these parameters to the standards specified in the technical specifications.

To improve the efficiency of monitoring and diagnostic tools, the user of the AUDC should be provided with a choice of one of the following modes:

- dictionary mode ("journal") of reference signatures, for given types of digital boards. Such a dictionary of reference signatures of digital boards makes it possible to control the state of the digital circuit according to them in an arbitrary order, looking for incorrect or unstable signatures;

Error backtracking mode according to a given fault finding algorithm in a digital board. In this mode, the operator receives instructions for sequential control of a set of points, which allows the operator with a probe, starting from an incorrect signature, to determine the entire chain of signatures leading to a faulty element or circuit node with the accuracy that signature analysis methods provide.

At the same time, at the end of the control and diagnostic procedures, automatic documentation and storage of the results should be provided in the AUDCP:

Date and time of the malfunction;

The mode of operation of the digital system at the time of the occurrence of a malfunction;

The method and means used to search for and localize the fault location;

Locations and causes of failure;

Time characteristics of detection, search and localization of the fault location;

The operator who diagnosed the problem.

The basic state of a digital device is goodsuch a state of the device in which it meets all the requirements of technical documentation. IN otherwise, the device is in one of the failed states.

If it is established that the digital device is faulty, then the second task is solved: a circuit fault search is carried out, the purpose of which is to determine the location and type of fault.

Digital device failures result from the use of faulty components, open or short circuits in interconnects, improper circuit operation, design and manufacturing errors, and a number of other factors.

For a scientifically based choice of methods and diagnostic tools, it is necessary to carefully study and analyze the malfunctions of digital devices, as well as to determine which class they belong to. In this case, the diagnostic method will be adequate to the digital device for which it is used, precisely to the extent that the fault model adequately taken as a basis.

In most cases, the following types of faults are considered:

1. Constant faults: constant zero and constant one, which means the presence of a constant level of logic zero or logic one at the inputs and outputs of the faulty logic element.

3. Faults of the "short circuit" type (bridge faults) appear when the inputs and outputs of logic elements are short-circuited and are divided into two types: faults caused by a short circuit of the inputs of the logic element, and faults of the feedback type.

4. Inverse faults describe physical defects in digital circuits, leading to the appearance of a fictitious inverter at the input or output of a logic element included in this circuit.

5. Entanglement faults are the entanglement of digital circuit connections and are caused by errors that occur during the design and manufacture of digital circuits that change the functions performed by the circuit.

Figure 1. shows the life cycle of digital systems in the period, their technical operation, which can be characterized through - failure rate:

Fig.1. Three stages of technical operation of digital systems

Three characteristic regions can be distinguished on the curve:

I. pre-operational training and testing.

II. normal operation.

III. aging, wear and tear and disposal.

During the first period of pre-operational tests, the majority of production defects and malfunctions are revealed. They account for up to 70 80% of system failures as a whole.

In the second period, the system goes through normal operation, so failures and malfunctions are observed with a minimum intensity - .

In the third period, it increases sharply due to degradation processes, and the system needs major repairs or disposal.

The nature and type of failures in these three periods of technical operation of the systems are mainly of different types: if production errors prevail in the first period, then in the third there is a sharp deviation in the numerical values ​​of the main parameters of the elements, due to degradation processes and eliminated to a certain extent by the method of adjustments and adjustments. An analysis of the causes and types of failures in different time periods allows you to actively intervene in the production process and minimize errors due to the influence of the human factor (train technical staff, equip them with advanced control and measuring equipment, etc.).

It is known that the primary source of violations of normal operationobject or the deterioration of one or another of its characteristics arephysical defects of the components of its elements, as well as the connections betweenthem. A malfunction as a physical phenomenon is called a defect, and the term "malfunction" is used either as the name of a defect model, or in the sense of a faulty state of an object.or its constituent parts.

Thus, a defect is understood as a physical phenomenon in the components of the device that caused the transitioninto a subset of faulty states. And a malfunction is a formalized representation of the fact of the manifestation of a defect in the form of incorrect signal values ​​at the inputs and outputs of the object. Term"defect" is related to the term "malfunction", but is not itssynonymous, that is, a malfunction is a specific conditionobject in which it may have one or more defects.Depending on the structure of the device, a defect may or may notlead to an error at the external outputs of the object, and an error is the wrong values ​​of the signals at the external outputs of the object, caused by malfunctions.

The failure rate of individual elements of digital systems has the following limits:

Failure rate - 10-6

I.S. 0.1 10 -6

Diode (0.2 0.5) 10-6

CPU 152 10-6

Transistor (0.05 0.30) 10-6

Resistor (0.01 0.1) 10-6

Printer 420 10-6

Soldering 0.0001 10 -6

RAM 300 10 -6

NMD 250 10 -6

NML 350 10 -6

Connectors (2.0 3.5) 10-6

Depending on the complexity and laboriousness of the localization of defects, the time of its detection varies widely.

The presence of defects significantly increases the cost of production, degrades the quality and reliability of the circuit.

The distribution of defects in different stages of the technological process is as follows:

1. Input control of products 1.9 ÷3.2% .

2. Picking 0.9 ÷ 1.2% .

3. Preparation and molding of elements 0.8 ÷1.0% .

4. Assembly 3 ÷ 4%.

5. Soldering 5 ÷ 6%.

6. Interoperational movements of products 0.4 ÷ 0.6%.

In general, up to 20% of printed circuit assemblies contain certain defects that need to be identified and corrected.

Tests show that:

Short circuits of printed conductors 34%;

Breaks of printed conductors 27%;

Wrong orientation 15%;

Missed and mistaken installed elements 17%;

Defective items 5% and other defects 2%.

Similar data on English technology show that:

The flow of good printed circuit assemblies is 67%, and 33% are defective.

The types of defects are as follows:

Short circuits 50%;

Missing elements 20%, and incorrectly installed elements 10%;

Faults active 10%, and passive 10%.

Types of integrated circuit defects are as follows:

Surface defects of IS 38.9%;

Case defects 26%;

Terminal defects 10.3%;

Connection defects 5.2%;

Metallization defects 6.6%;

Volumetric defects in - 6.6%;

Defects in oxide 6.4%.

As a result of the appearance of a defect, failures or failures are observed.

System (device) failure is a complete or partial loss of operability by the system (device), for the restoration of which it is necessary to repair (replace) the faulty element, block or device.

Thus, a complex system can have a huge number of states, which are conditionally divided into operable and faulty states.

Each state of the system is usually set by probabilistic parameters or mathematical models of varying degrees of complexity are developed, the degree of adequacy of which real process sometimes it is impossible to establish by any measurements. In an inoperable state, some functional parameters of the system go beyond the normal range. Therefore, with the help of technical diagnostics, information about the technical condition of the system is obtained (Fig. 2 ) to manage this state and return the system to a healthy state.

The graph of the technical state of the system is as follows.

Rice. 2 . Graph of the technical state of the system

Therefore, the main tasks of the technical operation of the system are: preventing the occurrence of failures, restoring the system in case of failures, assessing the state of the system, extending the state of readiness of the system, timely maintenance, etc.

The probability of the system being in a working state is expressed through the coefficient:

(1)

Where mean time between failures;

Average recovery time;

average maintenance time.

The optimal frequency of maintenance work depends on the availability of a sufficient number of experienced specialists (their performance of maintenance work), on the reliability of the functioning of the main elements of the systems, on the recovery time, etc. When carrying out maintenance work (adjustments, measurements of many system parameters, etc.) ) manual labor prevails and therefore, as a result of erroneous actions, personnel can introduce certain types of malfunctions and failures into existing systems.

There are various mathematical models of failures that describe this process with varying degrees of accuracy.

In view of the rarity of the occurrence of events in the form of failures, an ordinary flow of failures in time without aftereffect is described by the Poisson law:

(2)

Where is the number of emerging failures over a period of time with intensity -.

The probability of no failure in time is:

(3)

The uptime in the case of sudden failures of elements is distributed according to an exponential law with a probability density

where is the intensity of sudden failures.

Distributions of uptime for gradual failures:

(4)

Where mean uptime.

Distribution of uptime for two types of system:

(5)

Where and are normalizing coefficients.

The uptime for some elements obeys the Weibull distribution law:

(6)

Where and distribution parameters.

For the exponential law of uptime, the mean uptime is:

(7)

Mean recovery time for exponential law:

, (8)

Where is the intensity of system recovery.

If failures appear in accordance with the requirements of stationarity of random processes, then these models can take place at a certain stage of operation.

In cases of multiple failures or their grouping, one can consider the flow of failure packets (errors, failures) in time, which also form a stationary process.

1.3. Types and methods of control and diagnostics

Practical Implementation of Upgrading Pathstestability of existing and future digital systemsassociated primarily with the improvement of both traditional,and the development of qualitatively new methods and tools for assessing the technical condition of digital devices. All in allcase in the process of operation, digital systems are the source of various processes:electrical, thermal, electromagnetic, etc., which may be carriersessential diagnostic information about the technical condition.Consider existing methods control and diagnostics.

All electrical control methods can be divided into threemain groups:

• parametric,
• functional
• test

Parametric controlincludes the traditional method of measuring parameters on DC and time parameters: voltages,currents, resistances, frequency, duty cycle, fronts, pulse duration,signal propagation delay time, rise time,recession duration, etc.

In addition, leakage currents are subject to parametric measurements.input contacts, mutual conductivities of the outputs of microcircuits, gain factors, and in some cases the parameters of the input and outputsignals received in the process of simplifying the test of logical nodes.

Parametric control of electronic components is used whenchecking the correct installation of elements on the boards, localizationfaulty elements, control of input and output boards in conditionsproduction and operation. There are three main methods of parametric control of elements,installed on the board: the method of functional tests, the method of two-terminal networks, the method of potential separation. The analysis shows that the use of the first and second methods is associated with the desoldering of electronic elements from circuits, What in turn, can become a source of failures in the electronic node. At present, the third parametric method of measuring without breaking the links between the elements has become widespread..

Unlike parametric control,the task of functional control includes: serviceability check, troubleshooting,fault localization. Functional control methods differ in four main features: the method of generating inputinfluences, the method of generating output reactions, the method of comparisonoutput reactions of the system under test with true,method of analysis anddiagnosis. The latter includes four well-known ways: substitution, logical analysis,signature analysis and automatic diagnostics. Depending on the time scale in whichfunctional control is carried out, distinguish between static and dynamic. Static functional control is carried out atlow speed of the process, and dynamic - is carried out in real time at a speed close to the maximum. Accordingly, static control detectsrelatively simple faults, and dynamic monitoring allows you to identify complex dynamic faults.

Unlike functional control, in which only operating influences are used,test control is differentthe possibility of applying special test actions to the controlled circuit. When using the test method, the problem of synthesis arisesmonitoring and diagnostic tests for a given class of faults: constant faults, short circuits, breakselement malfunctions, etc. Of the most commonly used in test methods limitations of the type of faults, one can point to the fault "identical 0 " and "identical 1". As test methods,considering and not taking into account the logic of the scheme are used:truth table method, Boolean differentiation method, algorithm Armstrong method of X-cubes and method of D-cubes.

The first three methodsare used to detect single faults of the type "identical 0 " and "identical 1" in combinational circuits, as well as forpartial localization of faults.

Test construction methods:

A) the intersection method is applicable for objects with single faults and with enough a large number replaceable elements (up to 150 or more and up to 400 or more links between them). The method can be used to build diagnostic tools for combinational circuits with memory;

b) the truth table method can be successfully applied to a class of combinational circuits that are not too large (8÷10 inputs and 4-5 outputs) and have a number of specific faults not exceeding several hundred for detection and no more than a hundred for fault localization;

c) the Boolean differentiation method is used to test combinational circuits containing faults of the type "identical 0" or "identical 1";

d) Armstrong's algorithm is used to detect single faults of the "identical 0" and "identical 1" types in combinational circuits. In addition, this method is also suitable for partial localization of faults;

e) the X-cube method can be used to detect faults in both combinational and feedback circuits;

f) The D-cubes method is used both for checking faults of the "identical 0" and "identical 1" types, as well as for other faults.

All the considered methods of control and diagnostics differ sharply from each other in terms of information content, completeness, depth, reliability and performance of control and the complexity of diagnostics, requirements for the qualifications of specialists. It should be noted that the implementation of the most informative and highly productive methods is associated with the creation of complex monitoring and diagnostic tools.

1.4. Built-in control of digital systems

An objective trend in the development of modern digital systems is to expand the range of tasks they solve while simultaneously increasing the requirements for operational efficiency.A sharp increase in the number of elements in a piece of equipment, the complication of circuit solutions and functional connections of digital systems leads to significant difficulties in assessing their technical condition., detecting faults and identifying their causes under operating conditions. As a result, operating costs associated with maintenance and repair increase. O m of digital systems.

At present, the technological process Maintenance and repair of digital systems does not fully meet the modern requirements of their operation. This is explained by the fact that digital systems are not always equipped with special technical means to perform technological operations for maintenance and current repairs.

In addition, the operational and technical documentation used during maintenance does not contain recommendations for performing technological operations for current repairs and diagnosing failed functional units (boards) of a digital system, and the maintenance personnel do not have sufficient knowledge, experience and skills in the operation of modern digital systems, created on the basis of LSI, VLSI and microprocessor sets.

One of the main tasks of functional control in digital systems is the rapid detection of failures. technical means(TS).To solve this problem, it is necessary to control the state of each vehicle and the process of transmitting and processing information. Process control as a whole is systemic, in most cases it turns out to be simpler to implement and quite complete, its elements are included in all exchange protocols. Existing information transfer protocols provide for control of information fidelity, due to which the occurrence of any technical failure that causes violations in the process of transferring and processing information is detected.

One of the disadvantages of process control as a whole is the delay in the detection of a failure in the time interval from the moment the failure occurs to its detection. From this point of view, the functional control of the state of each TS of the system has certain advantages, thanks to which the failed TS can be blocked at the time of the failure. In this case, the failure must be detected and eliminated at the point of the technological process, the least remote in time and space from the point of occurrence of this failure. In a more general case, a real functional control system detects failures only with a certain probability. Failures that are not fixed by control are detected with a time delay, which is generally a random value.

Due to additivity, this delay is added to the recovery time:,

Where random recovery time, calculated from the moment the failure is detected until the moment of full recovery; specified in s This is a random failure detection delay time, calculated from the time the failure actually occurred to the time it is detected.

Therefore, one of the indicators of the quality of the functional control of the TS is the probability of operational(i.e. at the time of occurrence or with a given allowable delay) failure detection .

To ensure a unified strategy for monitoring and diagnosing digital systems, it is advisable to use two levels: the upper level control and diagnostics with an accuracy of TEC based on built-in control tools, the lower level fault diagnosis using technical diagnostic tools to a faulty element in the TEC.

In this regard, one of the effective solutions to the problem of control of a digital system is the use of the principle of built-in control, which means that a digital system and its components are designed in such a way as to provide the possibility of built-in control without the participation of any external equipment. Embedded control methods can be hierarchically redistributed between different levels from component parts to the digital system as a whole. Built-in monitoring allows the digital system to be tested while performing its main functions and essentially increases the operational reliability of the system because it allows failures to be detected as soon as they occur.

Built-in controls provide the following key benefits:

a) a significant reduction in the recovery time of the system and, accordingly, an increase in the overall operational readiness;

b) reduction in the number of maintenance personnel providing repair and restoration work;

c) reducing the types of repairs and spare parts by increasing the reliability of control.

However, it should be taken into account that the means of built-in operational control have a dual effect on the characteristics of the controlled system: on the one hand, the reliability of control increases and the time for detecting a malfunction decreases, on the other hand, the amount of additional equipment increases, which in turn leads to a decrease in the reliability of the system itself. Thus,built-in operational controls, providing a gain inreliability of control, lead to a certain loss in the reliability of controlled equipment. In this regard, the search for a reasonablethe optimum between the completeness of coverage of the built-in control of the system and the volume of built-in controls is an urgent task. Accountinginfluence of the volume of built-in control on the performance of the system will allow you to optimally redistribute resources betweenbuilt-in and external means of control and diagnostics. That's whyfor a reasonable choice of built-in control, it is necessary to carry outstudies of the impact of the scope of built-in controls on suchcharacteristics like readiness factor, probability of detectionfaults and average recovery time of the digital system.

Exist following parameters efficiency of the built-in control system:

the availability factor of a controlled system with a built-in system;

the probability of detecting a malfunction by the control device;

breakthrough in reliability of the controlled device with the control system;

gain in reliability when using built-in control;

Mean time between failures of a controlled system with a built-in control system;

the average recovery time of a controlled system with a built-in control system.

As shown in the criterion for evaluating the effectiveness of the control system is the loss in the reliability of the controlled device with the built-in control system. It is determined by the following formula.

, (9)

where is the probability of failure-free operation of the original (not controlled) circuit;

probability of failure-free operation.

In turn, the probability of failure-free operation of the original circuit can be defined as

, (10)

Where is the parameter of the failure rate of all equipment,

recovery intensity of the controlled system

Probability of failure-free operation of the control

(11)

Where and under which the control system is considered serviceable.

The general expression for the loss in the reliability of a controlled system with a built-in control tool

The gain in reliability when using the built-in control system is determined according to

, (13)

where is the reliability of the functioning of the monitored and control device in the verification process, which is calculated by the formula

. (14)

Substituting this expression into the formula, we get

. (15)

Graphs of dependence ∆Р and ∆ D on δ for different values ​​of the probability of fault detection Р update and the probability of failure-free operation of the original system Р ref shown in Figure 5, 6, 7, 8.

Fig. 5. Graph of dependencies and for and different values ​​of the probability of failure-free operation of the original circuit

Fig.6. Graph of dependencies and for and different sizes of the probability of failure-free operation of the original circuit

Rice. Fig. 7. Graph of dependencies and for and different values ​​of the probability of failure-free operation of the original circuit

Rice. 8. Graph of dependencies and for and different values ​​of the probability of failure-free operation of the original circuit

Based on the graphs shown in fig. 5, 6, 7, 8, it is possible to obtain the dependence of the optimal value of the volume of built-in control of a digital system depending on the probability of detecting a malfunction for various values ​​of the probability of failure-free operation of the original circuit. This dependence is shown in Table 1, and the dependency graph based on the results of this table is shown in Fig. 9.

Table 1.

Dependence of the optimal on for different values ​​of the probability of failure-free operation of the original circuit

Rice. 9. Dependence plot for different values ​​of the probability of failure-free operation of the original circuit

From the graph shown in fig. It can be seen from Table 1 that, for small values, the values ​​of the optimal volume of built-in control are large and, for various probabilities of failure-free operation of the original (controlled) circuit, are somewhat different from each other. As the value increases, the value decreases. And if the value approximately equal to 30% was determined as the upper limit of the volume of built-in control, then the value approximately equal to 10% can be considered the lower limit. Thus, the effective value of the built-in control volume of a digital system lies in the range from 10% to 30% of the volume of controlled equipment.

Homework: § abstract.

Fixing the material:

Answer the questions:

1. How characterized Features of control and diagnostics of digital boards with LSI and VLIS?
2. What featuresMicroprocessor systems ( MPS) do not allow the use of traditional equipment?
3. What are the common features of digital boards based on LSI, VLSI and MPC that determine the complexity of their control?
4. What tasks of control and diagnostics need to be solved in the conditions of operation of digital systems?
5. What does the analysis of the nomenclature and technical data of digital boards and their components include?
6. What kind of analysis is carried out in order to determine the main quantitative indicators of the operational reliability of digital boards?
7. Explain Dictionary Mode, Error Tracking Back Mode. What are they used for?
8. What results are saved at the end of control and diagnostic procedures?
9. What is the main state of a digital device?
10. What types of faults are considered in most cases?
11. Explain the three steps in the technical operation of digital systems
12. What is DEFECT? How is it different from failure?
13. What is a system (device) failure?
14. Define and explainparameter control.
15. Define and explainfunctional control.
16. Define and explaintest control.
17. What are the main tasks of functional control in digital systems?
18. Built-in control reveal its meaning.
19. Which Are there benefits inherent in Embedded Controls?

Literature:

Amrenov S. A. "Methods for monitoring and diagnosing systems and communication networks" LECTURE SUMMARY -: Astana, Kazakh State Agrotechnical University, 2005

I.G. Baklanov Testing and diagnostics of communication systems. - M.: Eco-Trends, 2001.

Birger I. A. Technical diagnostics. M .: "Engineering", 1978. 240, p.

Aripov M.N., Dzhuraev R.Kh., Jabbarov Sh.Yu."TECHNICAL DIAGNOSIS OF DIGITAL SYSTEMS" - Tashkent, TEIS, 2005

Platonov Yu. M., Utkin Yu. G.Diagnostics, repair and prevention personal computers. -M.: Hotline- Telecom, 2003.-312 p: ill.

M.E. Bushueva, V.V. BelyakovDiagnostics of complex technical systems Proceedings of the 1st meeting of the NATO project SFP-973799 Semiconductors . Nizhny Novgorod, 2001

Malyshenko Yu.V. TECHNICAL DIAGNOSIS part I lecture notes

Platonov Yu. M., Utkin Yu. G.Diagnosis of freezing and computer malfunctions / Series "Technomir". Rostov-on-Don: "Phoenix", 2001. 320 p.

PAGE\*MERGEFORMAT 12

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INTRODUCTION
In the last decade, digital systems have become widespread in telecommunications networks, which include:
- network elements (SDH transmission systems, digital automatic telephone exchanges (ATS), data transmission systems, access servers, routers, terminal equipment, etc.);
- systems for supporting the functioning of the network (network management, traffic control, etc.);
- business process support systems and automated settlement systems (billing systems).
The commissioning of digital systems puts the main task of ensuring their high-quality functioning. To build modern digital systems, an element base is used based on the use of large-scale integrated circuits (LSI), very large-scale integrated circuits (VLSI) and microprocessor sets (MPK), which can significantly improve the efficiency of systems - increase productivity and reliability, expand the functionality of systems, reduce weight, dimensions and power consumption. At the same time, the transition to the widespread use of LSI, VLSI and MPC in modern telecommunication systems has created, along with indisputable advantages, a number of serious problems in their operational maintenance, primarily related to control and diagnostic processes. This is because the complexity and number of digital systems in operation is growing faster than the number of skilled maintenance personnel. Since any digital system has a finite reliability, when failures occur in it, it becomes necessary to quickly detect, troubleshoot and restore the specified reliability indicators. Of particular importance is the fact that traditional methods of technical diagnostics require either highly qualified service personnel or complex diagnostic support. It should be noted that as the overall reliability of digital systems increases, the number of failures and operator intervention for troubleshooting decreases. On the other hand, along with an increase in the reliability of digital systems, there is a tendency for a certain loss of troubleshooting skills by maintenance personnel. A well-known paradox arises: the more reliable the digital system, the slower and less accurately faults are found, because service personnel are having difficulty accumulating experience in troubleshooting and localizing faults in advanced digital systems. In general, up to 70-80% of the recovery time of failed systems is the time of technical diagnostics, which consists of the time of searching and localizing failed elements. However, as operational practice shows, today engineers are not always ready to solve the tasks of technical operation of digital systems at the required level. Therefore, the increasing complexity of digital systems and the importance of ensuring their high-quality functioning requires the organization of its technical operation on a scientific basis. In this regard, engineers involved in the technical operation of digital systems must not only know how systems work, but also know how they do not work, how the state of inoperability manifests itself.
The decisive factor ensuring the high availability of digital systems is the availability of diagnostic tools that allow you to quickly search for and localize faults. This requires that engineers be well trained in preventing and recognizing the occurrence of unhealthy conditions and faults, i.e. were familiar with the goals, objectives, principles, methods and means of technical diagnostics. They knew how to correctly select, apply and effectively use them in operational conditions. The present tutorial course "Technical diagnostics of digital systems" is designed to draw due attention to the problems and tasks of technical diagnostics in the preparation of bachelors and masters in the field of telecommunications.

1. TECHNICAL OPERATION OF DIGITAL SYSTEMS AND DEVICES
1.1. Life cycle of a digital system
Digital devices and systems, like other technical systems, are created to meet the specific needs of people and society. An objectively digital system is characterized by a hierarchical structure, connection with the external environment, the interconnection of the elements that make up the subsystems, the presence of control and executive bodies, etc.
At the same time, all changes in a digital system, starting from the moment of its creation (the emergence of the need for its creation) and ending with complete utilization, form a life cycle (LC), characterized by a number of processes and including various stages and stages. Table 1.1 shows a typical digital system life cycle.
The life cycle of a digital system is a set of research, development, manufacture, handling, operation and disposal of the system from the beginning of the study of the possibilities of its creation to the end of its intended use.
The components of the life cycle are:
- the stage of research and design of digital systems, at which research and development of the concept are carried out, the formation of a quality level corresponding to the achievements of scientific and technological progress, the development of design and working documentation, the manufacture and testing of a prototype, the development of working design documentation;
- the stage of manufacturing digital systems, including: technological preparation of production; establishment of production; preparation of products for transportation and storage;
- the stage of circulation of products, which organizes the maximum preservation of the quality of finished products during transportation and storage;
- the stage of operation, which implements, maintains and restores the quality of the system, it includes: intended use, in accordance with the purpose; Maintenance; repair and recovery after failure.
On fig. 1.1 shows a typical distribution of stages and stages of the life cycle of a digital system. We will consider the tasks that arise at the stage of the life cycle associated with the operation of digital systems. So, the operation of the system is the stage of the life cycle at which its quality is realized (functional use), maintained (maintenance) and restored (maintenance and repair).
The part of operation, including transportation, storage, maintenance and repair, is called technical operation.
Table 1.1
Stages of the life cycle of a digital system

Exploratory research
Scientific research work (R&D)
Experimental design development (R&D)
industrial production
Exploitation
1. Statement of the scientific problem
2. Analysis of publications on the problem under study
3. Theoretical research and development of scientific concepts (research groundwork)
1. Development of terms of reference for research
2. Formalization of the technical idea
3. Market research
4. Feasibility study
1. Development of terms of reference for R & D
2. Development of a preliminary design
3. Making layouts
4. Development of a technical project
5. Creation of a working draft
6. Production of prototypes, their testing
7. Adjustment of design documentation (CD) based on the results
production and testing of prototypes
8. Technical preparation, production
1. Manufacturing and testing of the installation series
2. Adjustment of design documentation (CD) based on the results
manufacturing and testing of the installation series
3. Series production
1. Running in

2. Normal use

3. Aging
4. Repair or disposal
1.2. Main tasks of the theory of technical operation of digital systems
The classification of the main tasks of the technical operation of digital systems is shown in fig. 1.2. The theory of technical operation of systems considers mathematical models of degradation processes in the operation of systems, aging and wear of components, methods for calculating and evaluating the reliable functioning of systems, the theory of diagnosing and predicting failures and malfunctions in systems, the theory of optimal preventive measures, the theory of recovery and methods for increasing the technical resource of systems and etc. Due to the fact that these processes are mainly stochastic, in order to develop their mathematical model, analytical methods of the theory of random processes and the theory of queuing are used. At present, the statistical theory of decision making and the statistical theory of pattern recognition are successfully used for the same purposes.

The use of new directions of the mathematical theory of random processes in the development of models of the processes of technical operation of systems allows us to significantly expand our knowledge and successfully manage processes to increase the efficiency of functioning and improve the performance of fairly complex digital systems.
Therefore, at the first stage of the study, the following tasks are solved: optimal management of operational processes, development of optimal models for the operation of digital systems, drawing up optimal plans for the organization of maintenance, selection of optimal preventive procedures, development of methods for effective technical diagnostics and forecasting the technical condition of systems.
As indicated in, the main task of the theory of operation is to scientifically predict the states of complex systems or technical devices and development of recommendations on the organization of their operation using special models and mathematical methods of analysis and synthesis of these models. It should be noted that when solving the main problem of operation, a probabilistic-statistical approach is used to predict and control the states of complex systems and to model operational processes. Therefore, the theory of operation of digital systems in this period is rapidly being formed and is being intensively developed.
The technical operation of digital systems is reduced to optimizing the activity of human-machine systems and procedures for manipulating human influences on the functioning of systems. Therefore, the modes of operation of digital systems (Fig. 1.2) can be distinguished depending on the relationship of the human-machine system: pre-operational modes of systems, operating modes of systems, maintenance modes and repair modes of systems. The modes differ in certain stages and phases, the type of procedures for the control actions of technical personnel on the functioning of systems.
Operating modes depend mainly on the quality of the element base of the systems, the degree of use of microprocessor technology as part of the equipment, the complex of control and measuring equipment, the degree of training of technical personnel, as well as other circumstances related to the provision of spare elements of the systems. In addition, the operating modes are determined by the basic requirements for digital systems: fidelity of information transmission, delay time in information delivery, reliability of information delivery.
The operation of systems is the process of using them for their intended purpose while maintaining the systems in a technically sound condition, which consists of a chain of various sequential and planned activities: maintenance, prevention, control, repair, etc.
Maintenance of systems (Fig. 1.2) is characterized by three main stages: preventive maintenance, monitoring and evaluation of the technical condition, organization of maintenance. It is very difficult to determine the degree of influence of individual maintenance stages on the reliability of systems, but it is known that they have a significant impact on the quality and reliability of the systems.
Monitoring and evaluation of the technical condition of systems is carried out by monitoring the quality of functioning of system nodes, methods of technical diagnostics of failures and malfunctions, as well as the implementation of algorithms for predicting failures in systems.
1.3.General principles for building a technical operation system
The general task of the technical operation system (STE) is to ensure the uninterrupted operation of digital systems, therefore the main direction in the development of the STE is the automation of the most important technological processes of operation. The functional task of technical operation is the development of control actions that compensate for the influence of external and internal environments in order to maintain a given technical condition of digital systems. This common function is divided into two: general operation - management of the state of the external environment and technical operation - management of the state of the internal environment. At the same time, the management of the state of the internal environment consists in the management of its technical condition.

Rice. 1.3. Structural scheme automated system of technical operation: PNRM - subsystem of commissioning and repair work; STX - subsystem of supply, transportation and storage; SOISTE - STE information collection and processing subsystem; TTD - subsystem of test technical diagnostics; EOSTE - subsystem of ergonomic support of STE; USTE - subsystem of control of STE.
ASTE consists of two subsystems: the subsystem of technical operation in the preparation and use of digital systems (TEPI) and the subsystem of technical operation when using digital systems for their intended purpose (TEIN). Each of these subsystems contains a number of elements, the main of which are shown in Fig. 1.3. In more detail, the functions of the subsystems are given in Table. 1.2.
Table 1.2

Subsystem Basic functions of the NRM
Organization of commissioning of newly introduced digital systems, as well as current, medium and

overhaul

STX
Placement and replenishment of spare parts, supply bases and factories of manufacturers of spare parts, transportation and storage of spare parts

SOISTE
Planning the use of digital systems and maintaining operational documentation, collecting and processing operational data, developing recommendations for improving the STE

TTD
Determination of the technical condition, detection of a defect with a given depth, interaction with the subsystem of functional technical diagnostics (FTD)

EOSTE
Performing part of the TTD functions that require human participation, providing two-way communication in the “man-machine” system, participating in current repairs performed without stopping operation

USTE
Determining the order of TTD and EOSTE tasks for specific conditions, managing the recovery process, processing the results of performing TTD and EOSTE tasks, organizing interaction with other elements of digital systems

The presence of STE can significantly reduce the time for detecting faults in digital systems and, based on control information about the state of systems, prevent the occurrence of downtime in its operation. For this purpose, centers for the technical operation of digital systems are being organized, which perform the functions indicated in Fig. 1.4.

In modern digital systems, the statistical method of maintenance is common, which consists in the fact that repair and restoration work begins after the quality of functioning has reached a critical value. If, when monitoring the state of the elements of the systems, there are signs of a decrease in the quality of functioning, then they are disconnected from the network to restore working capacity.

The control of the functioning of digital systems is carried out by a set of parameters characterizing their performance.

Control of the functioning of digital systems is carried out according to the following characteristics; fidelity of message transmission; message transmission time; the probability of timely delivery of messages; average message delivery time, etc. The general scheme of functional control is shown in Fig. 1.5.

Rice. 1.4. Main functions of the technical operation center

Fig.1.5. Algorithm of the system of functional diagnostics of a digital system

2. BASES OF CONTROL AND TECHNICAL DIAGNOSIS OF DIGITAL SYSTEMS

2.1. Basic concepts and definitions

One of the most effective ways to improve the operational and technical characteristics of digital systems that have taken a dominant position in modern telecommunication systems is the use of methods and means of control and technical diagnostics during their operation.

Technical diagnostics is a field of knowledge that allows to separate the faulty and serviceable states of systems with a given reliability, and its purpose is to localize faults and restore the system to a healthy state. From the point of view of a systematic approach, it is advisable to consider the means of control and technical diagnostics as an integral part of the maintenance and repair subsystem, i.e., the technical operation system.

Consider the basic concepts and definitions used to describe and characterize the methods of control and diagnostics.

Maintenance is a set of works (operations) to maintain the system in good or operable condition.

Repair - a set of operations to restore the health and restore the resources of the system or its components.

Maintainability - a property of the system, which consists in adaptability to the prevention and detection of the causes of its failures and the restoration of a working state through maintenance and repair.

Depending on the complexity and scope of work, the nature of the malfunctions, two types of repair of digital systems are provided:

Unscheduled maintenance of the system;

Unscheduled average system repair.

Current repair - a repair performed to ensure or restore the system's operability and consisting in the replacement or restoration of its individual parts.

Medium repair - a repair performed to restore serviceability and partial restoration of a resource with the replacement or restoration of components of a limited range and control of the technical condition of the components, carried out to the extent established by the regulatory and technical documentation.

One of the important concepts in technical diagnostics is

technical condition of the object.

Technical condition - a set of properties of an object subject to change in the process of production or operation, characterized at a certain moment by the signs established by the regulatory and technical documentation.

Technical condition control - determination of the type of technical condition.

Type of technical condition - a set of technical conditions that satisfy (or do not satisfy) the requirements that determine the serviceability, operability or correct functioning of the object.

There are the following types of object state:

good or bad condition,

Working or non-working state,

Full or partial operation.

Serviceable - the technical condition in which the object meets all the established requirements.

Faulty - a technical condition in which the object does not meet at least one of the established requirements of regulatory characteristics.

Operable - a technical state in which the object is able to perform the specified functions, keeping the values ​​of the specified parameters within the established limits.

Inoperable - a technical condition in which the value of at least one specified parameter that characterizes the ability of an object to perform specified functions does not meet the established requirements.

Proper functioning is a technical state in which the object performs all those regulated functions that are required at the current time, while maintaining the values ​​of the specified parameters for their implementation within the established limits.

Incorrect functioning is a technical condition in which the object does not perform part of the regulated functions required at the current time or does not maintain the values ​​of the specified parameters for their implementation within the established limits.

From the definitions of the technical states of the object, it follows that in the state of health the object is always operable, in the state of health it functions correctly in all modes, and in the state of incorrect functioning it is inoperative and faulty. A properly functioning object may be inoperable, and therefore faulty. A healthy object can also be faulty.

Consider some definitions related to the concept of testability and technical diagnostics.

Testability is a property of an object that characterizes its suitability for testing by specified means.

The indicator of testability is a quantitative characteristic of testability.

The level of testability is a relative characteristic of testability, based on a comparison of the set of testability indicators of the object being evaluated with the corresponding set of basic indicators.

Technical diagnostics is the process of determining the technical condition of an object with a certain accuracy.

Defect search - diagnostics, the purpose of which is to determine the location and, if necessary, the cause and type of defect.

Diagnosis test - one or more test actions and the sequence of their execution, providing diagnosis.

A checking test is a diagnostic test to check the serviceability or operability of an object.

Defect search test - diagnostic test for defect search.

Technical diagnostic system - a set of means and an object of diagnostics and, if necessary, performers, prepared for diagnostics or carrying it out according to the rules established by the relevant documentation.

The result of the diagnosis is a conclusion on the technical condition of the object indicating, if necessary, the location, type and cause of the defect. The number of states that need to be distinguished as a result of diagnosis is determined by the depth of troubleshooting.

Fault search depth - the degree of detail in technical diagnostics, indicating to which component of the object the fault location is determined.

2.2. Tasks and classification of technical diagnostic systems

Increasingly increasing requirements for the reliability of digital systems necessitate the creation and implementation of modern methods and technical means of monitoring and diagnostics for various stages of the life cycle. As noted earlier, the transition to the widespread use of LSI, VLSI and MPC in digital systems has created, along with indisputable advantages, a number of serious problems in their operational maintenance, primarily related to monitoring and diagnostic processes. It is known that the cost of troubleshooting at the production stage is from 30% to 50% of the total cost of manufacturing devices. At the stage of operation, at least 80% of the recovery time of a digital system falls on the search for a faulty replaceable element. In general, the costs associated with the detection, troubleshooting and elimination of a malfunction increase by a factor of 10 with the passage of a malfunction through each technological stage and from the input control of integrated circuits to the detection of a failure at the operational stage are 1000 times more expensive. A successful solution to such a problem is possible only on the basis of an integrated approach to the issues of monitoring diagnostics, since diagnostic systems are used at all stages of the life of a digital system. This requires a further increase in the intensity of maintenance, restoration and repair work at the production and operation stages.

The general tasks of monitoring and diagnosing digital systems and its components are usually considered from the point of view of the main stages of development, production and operation. Along with general approaches to solving these problems, there are also significant differences due to the specific features inherent in these stages. At the stage of development of digital systems, two tasks of control and diagnostics are solved:

1. Ensuring the traceability of the digital system as a whole and its

Component parts.

2. Debugging, checking the health and performance of components

And the digital system as a whole.

When monitoring and diagnosing in the conditions of production of a digital system, the following tasks are solved:

1. Identification and rejection of defective components and assemblies at an early stage

Manufacturing stages.

2. Collection and analysis of statistical information about defects and types

Faults.

3. Reduction of labor intensity and, accordingly, the cost of control and

Diagnostics.

Control and diagnostics of a digital system under operating conditions have the following features:

1. In most cases, localization of faults on

The level of a structurally removable unit, as a rule, a typical

Replacement element (TEZ).

2. There is a high probability of occurrence by the time of repair no more than one

Faults.

3. Most digital systems have some

Possibilities of control and diagnostics.

4. Early detection of pre-failure conditions is possible when

Preventive checkups.

Thus, for the object subject to technical diagnostics, the type and purpose of the diagnostic system must be established. Accordingly, the following main areas of application of diagnostic systems are established:

a) at the stage of production of the object: in the process of adjustment, in the process

acceptance;

b) at the stage of operation of the facility; during maintenance in

In-process application, in-process maintenance

Storage, during maintenance during transportation;

c) when repairing the product: before repair, after repair.

Diagnostic systems are designed to solve one or more tasks: checking serviceability; health checks; functional checks: search for defects. At the same time, the components of the diagnostic system are: the object of technical diagnostics, which is understood as an object or its components, the technical condition of which is to be determined, means of technical diagnostics, a set measuring instruments, means of switching and interfacing with the object.

Technical diagnostics (TD) is carried out in the technical diagnostics system (STD), which is a set of means and an object of diagnostics and, if necessary, performers, prepared for diagnostics and carrying it out according to the rules established by the documentation.

The components of the system are:

the object of technical diagnostics (OTD), which is understood as systems or its components, the technical condition of which is to be determined, and the means of technical diagnostics - a set of measuring instruments, means of switching and interfacing with the TTD.

The system of technical diagnostics works in accordance with the TD algorithm, which is a set of instructions for diagnosing.

The conditions for conducting TD, including the composition of diagnostic parameters (DP), their maximum permissible minimum and maximum pre-failure values, the frequency of diagnosing a product and the operational parameters of the means used, determine the mode of technical diagnostics and control.

Diagnostic parameter (attribute) - a parameter used in the prescribed manner to determine the technical condition of an object.

Technical diagnostic systems (STD) can be different in their purpose, structure, installation site, composition, design, circuit solutions. They can be classified according to a number of features that determine their purpose, tasks, structure, composition of technical means:

according to the degree of coverage of the CTD; by the nature of the interaction between the CTD and the system of technical diagnostics and control (STDC); on the means of technical diagnostics and control used; according to the degree of automation of the OTD.

According to the degree of coverage, technical diagnostic systems can be divided into local and general. Local systems are understood as technical diagnostic systems that solve one or more of the above tasks - determining the operability or finding the place of failure. General - they call technical diagnostic systems that solve all the tasks of diagnostics.

According to the nature of the interaction of the OTD with the means of technical diagnostics (SrTD), technical diagnostic systems are divided into:

systems with functional diagnostics, in which the solution of diagnostic problems is carried out in the process of functioning of the DTD according to its intended purpose, and systems with test diagnostics, in which the solution of diagnostic problems is carried out in a special operating mode of the DTD by applying test signals to it.

According to the means of technical diagnostics used, TD systems can be divided into:

Systems with universal means of TDK (for example, computers);

Systems with specialized tools (stands, simulators, specialized computers);

Systems with external means, in which the means and DTD are structurally separated from each other;

systems with built-in tools, in which DTD and STD constructively represent one product.

According to the degree of automation, the technical diagnostics system can be divided into:

Automatic, in which the process of obtaining information about the technical condition of the OTD is carried out without human intervention;

Automated, in which the receipt and processing of information is carried out with the partial participation of a person;

Non-automated (manual), in which the receipt and processing of information is carried out by a human operator.

The means of technical diagnostics can be classified in a similar way: automatic; automated; manual.

With regard to the object of technical diagnostics, diagnostic systems should: prevent gradual failures; identify implicit failures; search for faulty nodes, blocks, assembly units and localize the place of failure.

2.3. Indicators of diagnostics and testability

As mentioned earlier, the process of determining the technical condition of an object during diagnosis involves the use of diagnostic indicators.

Diagnostic indicators represent a set of characteristics of an object used to assess its technical condition. Diagnostic indicators are determined during the design, testing and operation of the diagnostic system and are used when comparing various options for the latter. According to the following diagnostic indicators are established:

1. Probability of error in diagnosing a type - the probability of the joint occurrence of two events: the diagnosing object is in a technical condition, and as a result of diagnosing it is considered to be in a technical condition (when the indicator is the probability of correctly determining the technical condition of the diagnosing object)

, (2.1)

where is the number of states of the diagnostic tool;

A priori probability of finding the object of diagnosis in the state;

A priori probability of finding the diagnostic tool in the state;

The conditional probability that, as a result of diagnosing, the diagnosing object is recognized as being in a state under the conditions that it is in a state and the diagnostic tool is in a state;

Conditional probability of obtaining the result "diagnosing object is in state" provided that the diagnostic tool is in state;

The conditional probability of finding the diagnosing object in the state under the conditions that the result "the diagnosing object is in the state" is received and the diagnosing tool is in the state.

2. A posteriori probability of a diagnostic error of the type - the probability of finding the object of diagnosis in the state, provided that the result "the object of diagnosis is in technical condition" (when =) is obtained, the indicator is the a posteriori probability of correctly determining the technical condition).

, (2.2)

where is the number of object states.

3. The probability of correct diagnosis D is the total probability that the diagnosis system determines the technical condition in which the object of diagnosis is actually located.

. (2.3)

4. Average operational duration of diagnosis

The mathematical expectation of the operational duration of one

multiple diagnosis.

, (2.4)

where is the average operational duration of diagnosing an object that is in a state;

The operational duration of diagnosing an object that is in a state, provided that the diagnostic tool is in a state.

The value includes the duration of the auxiliary diagnostic operations and the duration of the actual diagnosis.

5. The average cost of diagnosing - the mathematical expectation of the cost of a single diagnosis.

, (2.5)

where is the average cost of diagnosing an object that is in a state;

The cost of diagnosing an object that is in a state, provided that the diagnostic tool is in a state. The value includes the depreciation costs of diagnosing, the costs of operating the diagnosing system and the cost of depreciation of the diagnosing object.

6. Average operational complexity of diagnosing - the mathematical expectation of operational labor intensity of a single diagnosis

, (2.6)

where is the average operational complexity of diagnosing when the object is in the state;

The operational complexity of diagnosing an object that is in a state, provided that the diagnostic tool is in a state.

7. The depth of the search for a defect L - a characteristic of the search for a defect, set by indicating the component of the object of diagnosis or its section with an accuracy to which the location of the defect is determined.

Let us now consider the testability indicator. Traceability is ensured at the stages of development and manufacture and should be established in the technical specifications for the development and modernization of the product.

Accordingly, the following testability indicators and formulas for their calculation are established:

1. The coefficient of completeness of the check of serviceability (operability, correct functioning):

, (2.7)

where is the total failure rate of the tested components of the system at the accepted level of division;

is the total failure rate of all components of the system at the accepted division level.

2. Search depth coefficient:

, (2.8)

Where is the number of uniquely distinguishable components of the system at the accepted level of division, with an accuracy up to which the location of the defect is determined;

is the total number of components of the system at the accepted level of division, with an accuracy up to which it is required to determine the location of the defect.

3. Diagnosis test length:

(2.9)

where || - number of test actions.

4. Average time to prepare the system for diagnosis by a given number of specialists:

, (2.10)

where is the average installation time of removal measuring transducers and other devices necessary for diagnosing;

- the average time of machine-dismantling work on the systems required to prepare for diagnostics.

5. Average laboriousness of preparation for diagnosis:

, (2.11)

where is the average laboriousness of installing and removing transducers and other devices necessary for diagnosing;

- the average laboriousness of installation - dismantling works on the object to provide access to control points and bring the object to its original state after diagnosing.

6. System redundancy ratio:

(2.12)

where is the volume of components introduced to diagnose the system;

The mass or volume of the system.

7. Coefficient of unification of interface devices and systems with diagnostic tools:

(2.13)

where is the number of unified interface devices.

The total number of interface devices.

8. The coefficient of unification of the parameters of the system signals:

(2.14)

Where - the number of unified parameters of the system signals used in the diagnosis;

The total number of signal parameters used in diagnostics.

9. The coefficient of labor intensity of preparing the system for diagnosis:

(2.15)

where is the average operational complexity of diagnosing the system;

Average laboriousness of preparing the system for diagnostics.

10. The coefficient of use of special diagnostic tools:

(2.16)

where is the total mass or volume of serial and special diagnostic tools;

– mass or volume of special diagnostic tools.

11. Level of testability in the assessment:

differential: (2.17)

where is the value of the testability indicator of the system being evaluated; - the value of the basic indicator of testability.

Complex, (2.18)

where is the number of testability indicators, the totality of which is used to evaluate the level of testability;

Weight coefficient of the th indicator of testability.

3. ELEMENTS OF DIGITAL SYSTEMS AND PROBLEMS OF INCREASING THEIR RELIABILITY

3.1. Digital systems, the main criteria for their reliability

The main task of modern digital systems is to increase the efficiency and quality of information transmission. The solution to this problem is developing in two directions: on the one hand, methods for transmitting and receiving discrete messages are being improved to increase the speed and reliability of transmitted information while limiting costs, on the other hand, new methods are being developed for building digital systems that ensure high reliability of their work.

This approach requires the development of digital systems that implement complex control algorithms under conditions of random influences with the need for adaptation and have the property of fault tolerance.

The use of LSI, VLSI and MPC for these purposes makes it possible to ensure high efficiency of information transmission channels and the ability to quickly restore the normal functioning of digital systems in case of failure.

In the future, under the modern digital system we will understand such a system, which is built on the basis of LSI, VLSI and MPC.

The block diagram of the digital system is shown in Figure 3.1. The transmitting part of the digital system performs a number of transformations of a discrete message into a signal. The set of operations associated with the transformation of transmitted messages into a signal is called the transmission method, which can be described by the operator relation

(3.1)

where is the transmission mode operator;

encoding operator;

Modulation operator;

Random process of occurrence of failures and failures in the transmitter.

The appearance of failures and failures in the transmitter leads to a violation of the condition >

Signals transmitted in a propagation medium undergo attenuation and distortion in it. Therefore, the signals arriving at the receiving point may differ significantly from those transmitted by the transmitter.

Fig 3.1. Structural diagram of a digital system

The influence of the medium on the signals propagated in it can also be described by the operator relation

(3.2)

where is the distribution medium operator.

In the communication channel, interference is superimposed on the transmitted signal, so that when the signal is transmitted, a distorted signal acts at the receiver input:

, (3.3)

where is a random process corresponding to one of the noises;

Number of independent interference sources.

The task of the receiver is to determine which message was transmitted from the received distorted signal. The set of receiver operations can be described by the operator relation:

(3.4)

where is the reception method operator;

Demodulation operator;

decoding operator;

Random process of occurrence of failures and failures in the receiver.

The completeness of the correspondence of the transmitted sequence depends not only on the corrective capabilities of the coded sequence, the level of the signal and interference and their statistics, the properties of the decoding devices, but also on the ability of the digital system to correct errors caused by hardware failures and failures of the transmitter and receiver and . The considered approach allows us to describe the process of information transfer mathematical model, which makes it possible to identify the influence of various factors on the efficiency of digital systems and outline ways to improve their reliability.

It is known that all digital systems are unrecoverable and recoverable. The main criterion for the reliability of a non-recoverable digital system is the probability of failure-free operation:

(3.5)

is the probability that no failure will occur in a given time interval t;

Where -

? – failure rate;

The number of elements in the digital system;

The failure rate of one element of a digital system.

The main criterion for the reliability of recoverable digital systems is the availability factor

, (3.6)

which characterizes the probability that the system will be in good condition at an arbitrarily chosen point in time;

Where is the mean time to failure;

This is the average value of the duration of continuous operation of the system between two failures.

, (3.7)

where N is the total number of failures;

Running time between () and failure.

Recovery time. Average system downtime caused by finding and fixing a failure.

, (3.8)

where is the failure duration.

where is the intensity of restoration, characterizes the number of restorations per unit of time.

3.2. Ways to improve the reliability of digital systems

Modern digital systems are complex geographically distributed technical complexes that perform important tasks for the timely and high-quality transmission of information.

Maintaining and providing the necessary repair and restoration work for complex digital systems is an important issue.

When choosing digital systems, you need to make sure that their manufacturers are ready to implement technical support during not only the warranty, but the entire service life, i.е. before reaching the limit state. Thus, when making a decision to purchase digital systems, operators need to take into account the long-term costs of its maintenance and repair.

It should be noted that the quality of the services offered, as well as the amount of costs incurred by the operator company in its activities, largely depends on the preparation and organization of the process of maintenance and repair of digital systems. Therefore, the task of improving the methods of maintenance and repair of geographically distributed digital systems is becoming increasingly important.

It is known that the requirements of international standards in the field of quality oblige the telecom operator as a service provider to include in the area of ​​quality systems - maintenance and repair of digital systems.

As the international experience of developed countries shows, in which the period of mass digitalization of the telecommunications network and the introduction of fundamentally new services has already passed, this task is effectively solved by creating a developed infrastructure for organizational and technical support, which also includes a system of service centers and repair centers.

Therefore, suppliers of digital systems should organize centers after-sales service for the implementation of warranty and post-warranty maintenance of its equipment, its current operation and repair.

Typically, the structure of the service center system includes:

The main service center, which coordinates the work of all other service centers and has the ability to perform the most complex types of work;

Regional service centers;

Telecom operator's technical service.

However, as practice shows, along with the high quality of the supplied equipment and its wide functionality, a number of problems arise:

Insufficient development (and in some cases absence) of the service network for the supplied digital systems;

There are more digital system providers than service centers;

The high cost of repairing digital systems.

In this regard, suppliers must be subject to appropriate requirements for the organization of maintenance of the supplied equipment and the timing of the replacement of faulty components of digital systems.

Since the level of convenience of the maintenance functions of digital systems varies from system to system, operation with various systems requires a different degree of training of service personnel. As practice shows, telecommunication equipment suppliers build their strategy for organizing service support in different ways:

Creation of the main service center of technical support;

Creation of a developed network of regional support centers;

Support through a network of distributors and a representative office;

Dealer network support.
Currently, there is a wide variety of forms, methods and types of maintenance. Services to customers are provided in four different forms:

Self-service by the customers themselves;

On-site service of the equipment;

Service in centers that do not repair, but replace;

Service in repair centers.

It should be especially noted that at present there is no single concept of service maintenance.

1. Some operator companies are of the opinion that the main task is to speed up repairs, which is achieved by replacing boards and even blocks, which then go through a full cycle of control and restoration of their performance in repair centers equipped with a set of modern diagnostic equipment.

2. Other operator companies prefer to move to element-level repairs, for which they use the latest diagnostic tools of high functional complexity to localize faults.

Therefore, an integral part of maintenance and repair systems as a system for managing the state of digital systems is a system of technical diagnostics. At present, it is generally recognized that one of the important ways to improve the operational reliability and, ultimately, the quality of the functioning of digital systems is to create an effective system of technical diagnostics.

Therefore, the solution of maintenance and repair tasks involves the use of an appropriate system for technical diagnostics of digital systems at the stage of their operation, which should provide a two-stage troubleshooting strategy in digital systems with a search depth, respectively, to a typical replacement element (TEZ), board and microcircuit. Taking into account the expansion of the range of digital systems, there is a need to reduce the requirements for the qualification of maintenance personnel of technical diagnostic systems, especially for service and repair centers. Diagnostic equipment intended for these centers should have, if possible, the minimum weight and size indicators and ensure that the specifics of each diagnostic object are taken into account.

Currently, the following main areas of work are known to improve the reliability of the functioning of digital systems:

1. First of all, reliability is enhanced by the use of highly reliable components. This direction is associated with significant costs and provides only a solution to the problem of reliability, but not maintainability. Unilateral orientation in the creation of systems to achieve high reliability (due to the use of a more advanced element base and assemblies) to the detriment of maintainability, in many cases does not ultimately lead to an increase in the availability factor in real operating conditions. This is due to the fact that even highly qualified specialists using traditional technical diagnostic tools spend up to 70-80% of active repair time searching for and localizing faults in complex modern digital systems.

2. The second direction of increasing reliability is the duplication or redundancy of technical means and communication channels. This direction requires the investment of large economic and labor costs, which ultimately leads in some cases to unjustified waste, in addition, in this case, increased reliability of the switching devices themselves must be ensured.

3. This direction is associated with the improvement of operational and specifications, by improving the maintainability indicators by means of technical diagnostics. It should be noted that in the existing digital systems there are no tools that would allow for prompt selection of channel errors from errors caused by hardware sources in the transmitting and receiving parts (modems, codecs, synchronization devices, etc.). In such digital systems, the detection of the fact of failure, the search and localization of hardware sources of faults is carried out in the "Communication failure" mode. In addition, most of the existing monitoring and diagnostic tools are practically applicable in maintenance and repair modes, which leads to a large spatio-temporal gap between the occurrence and detection of faults. The latter, ultimately, leads to significant economic and time costs for finding and localizing the location of the source and the cause of malfunctions.

In this regard, in order to improve the maintainability indicators, it is necessary to provide special measures for the rapid detection of the occurrence of errors due to hardware sources, search and localization, as places for the appearance of failures and failures in the blocks of digital systems (modems, codecs, synchronization devices, etc.). etc.), and malfunctions in the functional diagram of a faulty node.

In order to maintain digital systems in a technically sound condition, a monitoring and diagnostics subsystem is created, which is a set of software and hardware designed to diagnose their technical condition and maintain (or restore) the required quality level of work. Means of control and diagnostics of digital systems allow accelerating the complex processes of detecting and eliminating failures, reducing equipment downtime.

The elements of digital systems include terminal equipment, channel-forming equipment, switching systems, etc.

On fig. 3.2. the block diagram of an element of a digital information transmission system is shown, where the control points are given. The control and monitoring device, along with the main signal conversion devices (UPS) and error protection (RCD), also controls the signal quality detector (DKS), the interface device (US) and the data terminal equipment (DTE). Control of digital systems allows you to identify

Fig.3.2. Structural diagram of a digital transmission system element

Information

faulty nodes, reduces the number of hardware errors, reduces downtime of terminal devices.

One of the main tasks is to evaluate the quality states of discrete channels, which are classified as up and down states.

It is known that the quality of discrete channels is estimated by the quality of information transmission over the channels:

Evaluation method through secondary statistical characteristics of signals (distortions of elements, signals of erasing errors);

Evaluation method through signal parameters;

Evaluation method through interference parameters.

The results of these evaluations are used both to diagnose the technical condition of the data transmission channel and to improve the fidelity of the received signal sequence.

The subsystem of technical diagnostics consists of hardware and software that provide an assessment of informative diagnostic features that allow diagnosing the technical conditions of digital systems by processing diagnostic information with a given probability and depth.

etc.................

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TECHNICAL DIAGNOSIS OF DIGITAL SYSTEMS

Tutorial

Tashkent 2006

Content

• Introduction
• 1. Technical operation of digital systems and devices
• 3 . Elements of digital systems and problems of increasing their reliability
• 3.1 Digital systems, the main criteria for their reliability
• 3.3 Analysis of the strategy for diagnosing and restoring the health of digital systems
• 4. Methods for monitoring and diagnosing digital systems
• 4.1 Features of modern digital systems as an object of control and diagnostics
• 4.2 Analysis of failure models of digital devices
• 4.3 Types and methods of control and diagnostics
• 4.4 Built-in control of digital systems
• 5. Technical means of control and diagnostics of digital devices
• 5.1 Logic probes and current indicators
• 5.2 Logic analyzers
• 5.3 Signature analyzer
• 5.4 Technique for measuring reference signatures and constructing troubleshooting algorithms using signature analysis
• Conclusion
• List of sources used
• The manual provides the basics of control and technical diagnostics of digital systems, analysis and classification of methods and means of control and diagnostics. The analysis of digital systems as an object of diagnostics, models of malfunctions of digital devices is carried out. An assessment of the effectiveness of the built-in control of digital systems was made. The issues of technical implementation of procedures for monitoring and diagnostics of digital devices based on signature analysis are considered.
• The textbook is intended for bachelors and masters studying the issues of maintenance and repair of digital systems, as well as for specialists in technical diagnostics of digital devices.

Introduction

In the last decade, digital systems have become widespread in telecommunications networks, which include:

network elements (SDH transmission systems, digital automatic telephone exchanges (ATS), data transmission systems, access servers, routers, terminal equipment, etc.);

network operation support systems (network management, traffic control, etc.);

business process support systems and automated settlement systems (billing systems).

The commissioning of digital systems puts the main task of ensuring their high-quality functioning. To build modern digital systems, an element base is used based on the use of large-scale integrated circuits (LSI), very large-scale integrated circuits (VLSI) and microprocessor sets (MPK), which can significantly improve the efficiency of systems - increase productivity and reliability, expand the functionality of systems, reduce weight, dimensions and power consumption. At the same time, the transition to the widespread use of LSI, VLSI and MPC in modern telecommunication systems has created, along with indisputable advantages, a number of serious problems in their operational maintenance, primarily related to control and diagnostic processes. This is because the complexity and number of digital systems in operation is growing faster than the number of skilled maintenance personnel. Since any digital system has a finite reliability, when failures occur in it, it becomes necessary to quickly detect, troubleshoot and restore the specified reliability indicators. Of particular importance is the fact that traditional methods of technical diagnostics require either highly qualified service personnel or complex diagnostic support. It should be noted that as the overall reliability of digital systems increases, the number of failures and operator intervention for troubleshooting decreases. On the other hand, along with an increase in the reliability of digital systems, there is a tendency for a certain loss of troubleshooting skills by maintenance personnel. A well-known paradox arises: the more reliable the digital system, the slower and less accurately faults are found, because service personnel are having difficulty accumulating experience in troubleshooting and localizing faults in advanced digital systems. In general, up to 70-80% of the recovery time of failed systems is the time of technical diagnostics, which consists of the time of searching and localizing failed elements. However, as operational practice shows, today engineers are not always ready to solve the tasks of technical operation of digital systems at the required level. Therefore, the increasing complexity of digital systems and the importance of ensuring their high-quality functioning requires the organization of its technical operation on a scientific basis. In this regard, engineers involved in the technical operation of digital systems must not only know how systems work, but also know how they do not work, how the state of inoperability manifests itself.

The decisive factor ensuring the high availability of digital systems is the availability of diagnostic tools that allow you to quickly search for and localize faults. This requires that engineers be well trained in preventing and recognizing the occurrence of unhealthy conditions and faults, i.e. were familiar with the goals, objectives, principles, methods and means of technical diagnostics. They knew how to correctly select, apply and effectively use them in operational conditions. This manual for the course "Technical diagnostics of digital systems" is designed to draw due attention to the problems and tasks of technical diagnostics in the preparation of bachelors and masters in the field of telecommunications.

digital system diagnostics control

1. Technical operation of digital systems and devices

1.1 Digital system life cycle

Digital devices and systems, like other technical systems, are created to meet the specific needs of people and society. An objectively digital system is characterized by a hierarchical structure, connection with the external environment, the interconnection of the elements that make up the subsystems, the presence of control and executive bodies, etc.

At the same time, all changes in a digital system, starting from the moment of its creation (the emergence of the need for its creation) and ending with complete utilization, form a life cycle (LC), characterized by a number of processes and including various stages and stages. Table 1.1 shows a typical digital system life cycle.

The life cycle of a digital system is a set of research, development, manufacture, handling, operation and disposal of the system from the beginning of the study of the possibilities of its creation to the end of its intended use.

The components of the life cycle are:

the stage of research and design of digital systems, at which research and development of the concept are carried out, the formation of a quality level corresponding to the achievements of scientific and technological progress, the development of design and working documentation, the manufacture and testing of a prototype, the development of working design documentation;

the stage of manufacturing digital systems, including: technological preparation of production; establishment of production; preparation of products for transportation and storage;

the stage of circulation of products, which organizes the maximum preservation of the quality of finished products during transportation and storage;

the stage of operation at which the quality of the system is realized, maintained and restored, it includes: intended use, in accordance with the purpose; Maintenance; repair and recovery after failure.

Figure 1.1 shows a typical distribution of stages and stages of the life cycle of a digital system. We will consider the tasks that arise at the stage of the life cycle associated with the operation of digital systems. So, the operation of the system is the stage of the life cycle at which its quality is realized (functional use), maintained (maintenance) and restored (maintenance and repair).

The part of operation, including transportation, storage, maintenance and repair, is called technical operation.

Table 1.1

Stages of the life cycle of a digital system

Exploratory research	Scientific research work (R&D)	Experimental design development (R&D)	industrial production	Exploitation
1. Statement of the scientific problem 2. Analysis of publications on the problem under study 3. Theoretical research and development of scientific concepts (research	1. Development technical assignments for research 2. Formalization technical idea 3. Market research 4. Technical economic justification	1. Development of technical assignments for OKR Sketch development 3. Making layouts 4. Development of technical 5. Create a worker 6. Manufacturing experienced samples, their testing 7. Adjustment design documentation (CD) on result manufacturing and testing of experienced samples 8. Technical training, production	1. Manufacturing and trial installation 2. Correction design documentation results manufacturing and tests installation 3. Serial production	1. Running in 2. Normal exploitation 3. Aging 4. Repair or disposal

Fig.1.1 Life cycle of a digital system

1.2 The main tasks of the theory of technical operation of digital systems

The classification of the main tasks of the technical operation of digital systems is shown in Figure 1.2. The theory of technical operation of systems considers mathematical models of degradation processes in the operation of systems, aging and wear of components, methods for calculating and evaluating the reliable functioning of systems, the theory of diagnosing and predicting failures and malfunctions in systems, the theory of optimal preventive measures, the theory of recovery and methods for increasing the technical resource of systems and etc. Due to the fact that these processes are mainly stochastic, in order to develop their mathematical model, analytical methods of the theory of random processes and the theory of queuing are used. At present, the statistical theory of decision making and the statistical theory of pattern recognition are successfully used for the same purposes.

Using new directions mathematical theory random processes in the development of models of the processes of technical operation of systems allows us to significantly expand our knowledge and successfully manage processes to increase the efficiency of functioning and improve the performance of fairly complex digital systems.

Fig. 1.2 Classification of tasks of technical operation of digital systems

Therefore, at the first stage of the study, the following tasks are solved: optimal management of operational processes, development of optimal models for the operation of digital systems, drawing up optimal plans for the organization of maintenance, selection of optimal preventive procedures, development of methods for effective technical diagnostics and forecasting the technical condition of systems.

As indicated in, the main task of the theory of operation is to scientifically predict the states of complex systems or technical devices and develop, using special models and mathematical methods of analysis and synthesis of these models, recommendations for organizing their operation. It should be noted that when solving the main problem of operation, a probabilistic-statistical approach is used to predict and control the states of complex systems and to model operational processes. Therefore, the theory of operation of digital systems in this period is rapidly being formed and is being intensively developed.

The technical operation of digital systems is reduced to optimizing the activity of human-machine systems and procedures for manipulating human influences on the functioning of systems. Therefore, the modes of operation of digital systems (Fig. 1.2) can be distinguished depending on the relationship of the human-machine system: pre-operational modes of systems, operating modes of systems, maintenance modes and repair modes of systems.

The modes differ in certain stages and phases, the type of procedures for the control actions of technical personnel on the functioning of systems.

Operating modes depend mainly on the quality of the element base of the systems, the degree of use of microprocessor technology as part of the equipment, the complex of control and measuring equipment, the degree of training of technical personnel, as well as other circumstances related to the provision of spare elements of the systems. In addition, the operating modes are determined by the basic requirements for digital systems: fidelity of information transmission, delay time in information delivery, reliability of information delivery.

The operation of systems is the process of their intended use while maintaining the systems in a technically sound condition, which consists of a chain of various sequential and planned activities: maintenance, prevention, control, repair, etc.

Maintenance of systems (Fig. 1.2) is characterized by three main stages: preventive maintenance, monitoring and evaluation of the technical condition, organization of maintenance. It is very difficult to determine the degree of influence of individual maintenance stages on the reliability of systems, but it is known that they have a significant impact on the quality and reliability of the systems.

Monitoring and evaluation of the technical condition of systems is carried out by monitoring the quality of functioning of system nodes, methods of technical diagnostics of failures and malfunctions, as well as the implementation of algorithms for predicting failures in systems.

1.3 General principles building a system of technical operation

The general task of the technical operation system (STE) is to ensure the uninterrupted operation of digital systems, therefore the main direction in the development of the STE is the automation of the most important technological processes of operation. The functional task of technical operation is the development of control actions that compensate for the influence of external and internal environments in order to maintain a given technical condition of digital systems. This general function is divided into two: general operation - management of the state of the external environment and technical operation - management of the state of the internal environment. At the same time, the management of the state of the internal environment consists in the management of its technical condition.

A possible structure of an automated STE is shown in Fig. 1.3.

Fig.1.3 Structural diagram of the automated system for technical operation: PNRM - subsystem for commissioning and repair work; STX - subsystem of supply, transportation and storage; SOISTE - STE information collection and processing subsystem; TTD - subsystem of test technical diagnostics; EOSTE - subsystem of ergonomic support of STE; USTE - subsystem of control of STE.

ASTE consists of two subsystems: the subsystem of technical operation in the preparation and use of digital systems (TEPI) and the subsystem of technical operation when using digital systems for their intended purpose (TEIN). Each of these subsystems contains a number of elements, the main of which are shown in Figure 1.3. In more detail, the functions of the subsystems are given in Table 1.2.

Table 1.2

Subsystem	Main functions
	Organization of commissioning of newly introduced digital systems, as well as current, medium and overhaul
	Placement and replenishment of spare parts, supply bases and factories of manufacturers of spare parts, transportation and storage of spare parts
	Planning the use of digital systems and maintaining operational documentation, collecting and processing operational data, developing recommendations for improving the STE
	Determination of the technical condition, detection of a defect with a given depth, interaction with the subsystem of functional technical diagnostics (FTD)
	Performance of a part of TTD functions that require human participation, provision of two-way communication in the "man-machine" system, participation in current repairs carried out without stopping operation
	Determining the order of TTD and EOSTE tasks for specific conditions, managing the recovery process, processing the results of performing TTD and EOSTE tasks, organizing interaction with other elements of digital systems

The presence of STE can significantly reduce the time for detecting faults in digital systems and, based on control information about the state of systems, prevent the occurrence of downtime in its operation. For this purpose, centers for the technical operation of digital systems are being organized, which perform the functions indicated in Fig. 1.4.

In modern digital systems, a statistical method of maintenance is common, which consists in the fact that repair and restoration work begins after the quality of functioning has reached a critical value. If, when monitoring the state of the elements of the systems, there are signs of a decrease in the quality of functioning, then they are disconnected from the network to restore working capacity.

The control of the functioning of digital systems is carried out by a set of parameters characterizing their performance.

Control of the functioning of digital systems is carried out according to the following characteristics; fidelity of message transmission; message transmission time; the probability of timely delivery of messages; average message delivery time, etc. The general scheme of functional control is shown in Fig. 1.5.

Fig.1.4 Main functions of the technical operation center

Fig.1.5 Algorithm of the system of functional diagnostics of a digital system

2. Fundamentals of control and technical diagnostics of digital systems

2.1 Basic concepts and definitions

One of the most effective ways improving the operational and technical characteristics of digital systems that have taken a dominant position in modern telecommunication systems is the use of methods and means of control and technical diagnostics during their operation.

Technical diagnostics is a field of knowledge that allows to separate the faulty and serviceable states of systems with a given reliability, and its purpose is to localize faults and restore the system to a healthy state. From the point of view of a systematic approach, it is advisable to consider the means of control and technical diagnostics as an integral part of the maintenance and repair subsystem, that is, the technical operation system.

Consider the basic concepts and definitions used to describe and characterize the methods of control and diagnostics.

Technical service- this is a set of works (operations) to maintain the system in good or operable condition.

Repair- a set of operations to restore the health and restore the resources of the system or its components.

maintainability- property of the system, which consists in adaptability to the prevention and detection of the causes of its failures and the restoration of a working state by carrying out maintenance and repair.

Depending on the complexity and scope of work, the nature of the malfunctions, two types of repair of digital systems are provided:

unscheduled maintenance of the system;

unscheduled average system repair.

Current repair- repair performed to ensure or restore the system's operability and consisting in the replacement or restoration of its individual parts.

Average repair- repair performed to restore serviceability and partial restoration of the resource with the replacement or restoration of components of a limited range and control of the technical condition of the components, performed to the extent established by the regulatory and technical documentation.

One of the important concepts in technical diagnostics is

technical condition of the object.

Technical state- a set of properties of an object subject to change in the process of production or operation, characterized at a certain moment by the signs established by the regulatory and technical documentation.

Control technical states- determination of the type of technical condition.

View technical states- a set of technical conditions that satisfy (or do not satisfy) the requirements that determine the serviceability, operability or correct functioning of the object.

There are the following types of object state:

good or bad condition,

working or non-working state,

full or partial operation.

serviceable- technical condition in which the object meets all the established requirements.

Faulty- technical condition in which the object does not meet at least one of the established requirements of regulatory characteristics.

workable- technical condition in which the object is able to perform the specified functions, keeping the values ​​of the specified parameters within the established limits.

Unworkable - a technical condition in which the value of at least one specified parameter characterizing the ability of an object to perform specified functions does not meet the established requirements.

correct functioning- a technical state in which the object performs all those regulated functions that are required at the current time, while maintaining the values ​​of the specified parameters for their implementation within the established limits.

Wrong functioning- a technical condition in which the object does not perform part of the regulated functions required at the current time or does not retain the values ​​of the specified parameters for their implementation within the established limits.

From the definitions of the technical states of the object, it follows that in the state of health the object is always operable, in the state of health it functions correctly in all modes, and in the state of incorrect functioning it is inoperative and out of order. A properly functioning object may be inoperable, and therefore faulty. A healthy object can also be faulty.

Consider some definitions related to the concept of testability and technical diagnostics.

Traceability- a property of an object that characterizes its suitability for monitoring by specified means.

Index traceability - quantitative characteristic testability.

Level traceability- relative characteristic of testability, based on a comparison of the set of testability indicators of the assessed object with the corresponding set of basic indicators.

Technical diagnosing- the process of determining the technical condition of an object with a certain accuracy.

Search defect- diagnosis, the purpose of which is to determine the location and, if necessary, the cause and type of defect.

Test diagnosing- one or more test actions and the sequence of their execution, providing diagnostics.

Checker test- a diagnostic test to check the serviceability or operability of an object.

Test search defect- diagnostic test to find a defect.

System technical diagnosing- a set of means and an object of diagnosis and, if necessary, performers, prepared for diagnosis or carrying it out according to the rules established by the relevant documentation.

The result of the diagnosis is a conclusion on the technical condition of the object indicating, if necessary, the location, type and cause of the defect. The number of states that need to be distinguished as a result of diagnosis is determined by the depth of troubleshooting.

Depth search malfunctions- the degree of detail in technical diagnostics, indicating to which component of the object the fault location is determined.

2.2 Tasks and classification of technical diagnostic systems

Increasingly increasing requirements for the reliability of digital systems necessitate the creation and implementation of modern methods and technical means of control and diagnostics for various stages of the life cycle. As noted earlier, the transition to the widespread use of LSI, VLSI and MPC in digital systems has created, along with indisputable advantages, a number of serious problems in their operational maintenance, primarily related to monitoring and diagnostic processes. It is known that the cost of troubleshooting at the production stage is from 30% to 50% of the total cost of manufacturing devices. At the stage of operation, at least 80% of the recovery time of a digital system falls on the search for a faulty replaceable element. In general, the costs associated with the detection, troubleshooting and elimination of a malfunction increase by a factor of 10 with the passage of a malfunction through each technological stage and from the input control of integrated circuits to the detection of a failure at the operational stage are 1000 times more expensive. A successful solution to such a problem is possible only on the basis of an integrated approach to the issues of monitoring diagnostics, since diagnostic systems are used at all stages of the life of a digital system. This requires a further increase in the intensity of maintenance, restoration and repair work at the production and operation stages.

The general tasks of monitoring and diagnosing digital systems and its components are usually considered from the point of view of the main stages of development, production and operation. Along with general approaches to solving these problems, there are also significant differences due to the specific features inherent in these stages. At the stage of development of digital systems, two tasks of control and diagnostics are solved:

1. Ensuring the testability of the digital system as a whole and its components.

2. Debugging, checking the serviceability and performance of the components and the digital system as a whole.

When monitoring and diagnosing in the conditions of production of a digital system, the following tasks are solved:

1. Identification and rejection of defective components and assemblies in the early stages of manufacturing.

2. Collection and analysis of statistical information about defects and types of failures.

3. Reduction of labor intensity and, accordingly, the cost of control and diagnostics.

Control and diagnostics of a digital system under operating conditions have the following features:

1. In most cases, it is sufficient to localize faults at the level of a structurally removable unit, as a rule, a typical replacement element (TEZ).

2. There is a high probability of occurrence of no more than one malfunction by the time of repair.

3. Most digital systems provide some monitoring and diagnostic capabilities.

4. Early detection of pre-failure conditions during preventive inspections is possible.

Thus, for the object subject to technical diagnostics, the type and purpose of the diagnostic system must be established. Accordingly, the following main areas of application of diagnostic systems are established:

a) at the stage of production of the object: in the process of adjustment, in the process of acceptance;

b) at the stage of operation of the facility; during maintenance during use, during maintenance during storage, during maintenance during transportation;

c) when repairing the product: before repair, after repair.

Diagnostic systems are designed to solve one or more tasks: checking serviceability; health checks; functional checks: search for defects. At the same time, the components of the diagnostic system are: the object of technical diagnostics, which is understood as an object or its components, the technical condition of which is to be determined, technical diagnostic tools, a set of measuring instruments, means of switching and interfacing with the object.

Technical diagnostics (TD) is carried out in the technical diagnostics system (STD), which is a set of means and an object of diagnostics and, if necessary, performers, prepared for diagnostics and carrying it out according to the rules established by the documentation.

The components of the system are:

an object technical diagnosing(OTD), which is understood as a system or its components, the technical condition of which is to be determined, and facilities technical diagnosing - a set of measuring instruments, means of switching and interfacing with OTD.

System technical diagnosing works in accordance with the TD algorithm, which is a set of instructions for diagnosing.

The conditions for conducting TD, including the composition of diagnostic parameters (DP), their maximum permissible minimum and maximum pre-failure values, the frequency of diagnosing a product and the operational parameters of the means used, determine the mode of technical diagnostics and control.

Diagnostic parameter (attribute) - a parameter used in the prescribed manner to determine the technical condition of an object.

Technical diagnostic systems (STD) can be different in their purpose, structure, installation site, composition, design, circuit solutions. They can be classified according to a number of features that determine their purpose, tasks, structure, composition of technical means:

according to the degree of coverage of the CTD; by the nature of the interaction between the CTD and the system of technical diagnostics and control (STDC); on the means of technical diagnostics and control used; according to the degree of automation of the OTD.

According to the degree of coverage, technical diagnostic systems can be divided into local and general. Local systems are understood as technical diagnostic systems that solve one or more of the above tasks - determining the operability or finding the place of failure. General - they call technical diagnostic systems that solve all the tasks of diagnostics.

According to the nature of the interaction of the OTD with the means of technical diagnostics (SrTD), technical diagnostic systems are divided into:

systems With functional diagnosticallysticky, in which the solution of diagnostic tasks is carried out in the process of functioning of the DTD for its intended purpose, and systems with test diagnostics, in which the solution of diagnostic problems is carried out in a special operating mode of the DTD by applying test signals to it.

According to the means of technical diagnostics used, the TD system can be divided into:

systems with universal means of TDK (for example, a computer);

systems co specialized means(stands, simulators, specialized computers);

systems With external means, in which the means and DTD are structurally separated from each other;

systems co built-in means, in which OTD and STD structurally represent one product.

According to the degree of automation, the technical diagnostics system can be divided into:

automatic, in which the process of obtaining information about the technical condition of the OTD is carried out without human participation;

automated in which the receipt and processing of information is carried out with the partial participation of a person;

non-automated ( manual), in which the receipt and processing of information is carried out by a human operator.

The means of technical diagnostics can be classified in a similar way: automatic; automated; manual.

With regard to the object of technical diagnostics, diagnostic systems should: prevent gradual failures; identify implicit failures; search for faulty nodes, blocks, assembly units and localize the place of failure.

2.3 Diagnostic and testability indicators

As mentioned earlier, the process of determining the technical condition of an object during diagnosis involves the use of diagnostic indicators.

Diagnostic indicators represent a set of characteristics of an object used to assess its technical condition. Diagnostic indicators are determined during the design, testing and operation of the diagnostic system and are used when comparing various options for the latter. According to the following diagnostic indicators are established:

1. Probability of error in diagnosing a type - the probability of the joint occurrence of two events: the diagnosing object is in a technical condition, and as a result of diagnosing it is considered to be in a technical condition (when the indicator is the probability of correctly determining the technical condition of the diagnosing object)

, (2.1)

where is the number of states of the diagnostic tool;

- a priori probability of finding the object of diagnosis in the state;

- a priori probability of finding the diagnostic tool in the state;

- conditional probability that, as a result of diagnosing, the diagnosing object is recognized as being in a state under the conditions that it is in a state and the diagnostic tool is in a state;

- conditional probability of obtaining the result "diagnosing object is in the state" provided that the diagnostic tool is in the state;

- conditional probability of finding the diagnosing object in the state under the conditions that the result "the diagnosing object is in the state" is received and the diagnosing tool is in the state.

2. A posteriori probability of an error in diagnosing a type - the probability of finding the object of diagnosis in a state, provided that the result "the object of diagnosis is in technical condition" (when =) is obtained, the indicator is the a posteriori probability of correctly determining the technical condition).

, (2.2)

where is the number of object states.

3. The probability of correct diagnosis D is the total probability that the diagnosis system determines the technical condition in which the object of diagnosis is actually located.

. (2.3)

4. Average operational duration of diagnosis

- the mathematical expectation of the operational duration of one

multiple diagnosis.

, (2.4)

where is the average operational duration of diagnosing an object that is in a state;

- the operational duration of diagnosing an object that is in a state, provided that the diagnostic tool is in a state.

The value includes the duration of the auxiliary diagnostic operations and the duration of the actual diagnosis.

5. The average cost of diagnosing - the mathematical expectation of the cost of a single diagnosis.

, (2.5)

where is the average cost of diagnosing an object that is in a state;

- the cost of diagnosing an object that is in a state, provided that the diagnostic tool is in a state. The value includes the depreciation costs of diagnosing, the costs of operating the diagnosing system and the cost of depreciation of the diagnosing object.

6. Average operational complexity of diagnosing - the mathematical expectation of operational labor intensity of a single diagnosis

, (2.6)

where is the average operational complexity of diagnosing when the object is in the state;

- operational complexity of diagnosing an object that is in a state, provided that the diagnostic tool is in a state.

7. The depth of the search for a defect L - a characteristic of the search for a defect, set by indicating the component of the object of diagnosis or its section with an accuracy to which the location of the defect is determined.

Let us now consider the testability indicator. Traceability is ensured at the stages of development and manufacture and should be established in the technical specifications for the development and modernization of the product.

Accordingly, the following testability indicators and formulas for their calculation are established:

1. The coefficient of completeness of the check of serviceability (operability, correct functioning):

, (2.7)

where is the total failure rate of the tested components of the system at the accepted level of division;

- total failure rate of all components of the system at the accepted level of division.

Search Depth Coefficient:

, (2.8)

where is the number of uniquely distinguishable components of the system at the accepted level of division, with an accuracy up to which the location of the defect is determined; - the total number of components of the system at the accepted level of division, with an accuracy to which it is required to determine the location of the defect.

Diagnosis test length:

(2.9)

where || - number of test actions.

4. Average time to prepare the system for diagnosis by a given number of specialists:

, (2.10)

where is the average installation time for removing measuring transducers and other devices necessary for diagnosing;

- the average time of machine-dismantling work on the systems required to prepare for diagnosis.

5. Average laboriousness of preparation for diagnosis:

, (2.11)

where is the average laboriousness of installing and removing transducers and other devices necessary for diagnosing;

- average labor intensity of installation - dismantling works on the object to provide access to control points and bring the object to its original state after diagnosing.

6. System redundancy ratio:

(2.12)

where is the volume of components introduced to diagnose the system;

is the mass or volume of the system.

7. Coefficient of unification of interface devices and systems with diagnostic tools:

(2.13)

where is the number of unified interface devices.

- total number of interface devices.

8. The coefficient of unification of the parameters of the system signals:

(2.14)

where is the number of unified parameters of the system signals used in diagnosing;

- total number of signal parameters used in diagnostics.

9. The coefficient of labor intensity of preparing the system for diagnosis:

(2.15)

where is the average operational complexity of diagnosing the system;

- average labor input of system preparation for diagnostics.

10. The coefficient of use of special diagnostic tools:

(2.16)

where is the total mass or volume of serial and special diagnostic tools;

- mass or volume of special diagnostic tools.

11. Level of testability in the assessment:

differential:

(2.17)

where is the value of the testability indicator of the system being evaluated; - the value of the basic indicator of testability.

Integrated

, (2.18)

Where - the number of testability indicators, the totality of which evaluates the level of testability;

- weight coefficient of the th indicator of testability.

3. Elements of digital systems and problems of improving their reliability

3.1 Digital systems, the main criteria for their reliability

The main task of modern digital systems is to increase the efficiency and quality of information transmission. The solution to this problem is developing in two directions: on the one hand, methods for transmitting and receiving discrete messages are being improved to increase the speed and reliability of transmitted information while limiting costs, on the other hand, new methods are being developed for building digital systems that ensure high reliability of their work.

This approach requires the development of digital systems that implement complex control algorithms under conditions of random influences with the need for adaptation and have the property of fault tolerance.

The use of LSI, VLSI and MPC for these purposes makes it possible to ensure high efficiency of information transmission channels and the ability to quickly restore the normal functioning of digital systems in case of failure. In the future, under the modern digital system we will understand such a system, which is built on the basis of LSI, VLSI and MPC.

The block diagram of the digital system is shown in Fig. 3.1. The transmitting part of the digital system performs a number of transformations of a discrete message into a signal. The set of operations associated with the transformation of transmitted messages into a signal is called the transmission method, which can be described by the operator relation

(3.1)

where is the transmission mode operator;

- encoding operator;

- modulation operator;

- a random process of occurrence of failures and failures in the transmitter.

The appearance of failures and failures in the transmitter leads to a violation of the condition > and an increase in the number of errors in the digital system. As a result, it is necessary to design the transmitter in such a way that the increase in the number of errors due to violation of the condition >

Signals transmitted in a propagation medium undergo attenuation and distortion in it. Therefore, the signals arriving at the receiving point may differ significantly from those transmitted by the transmitter.

Fig 3.1 Structural diagram of a digital system

The influence of the medium on the signals propagated in it can also be described by the operator relation

(3.2)

where is the distribution medium operator.

In the communication channel, interference is superimposed on the transmitted signal, so that during signal transmission a distorted signal acts at the receiver input:

, (3.3)

where is a random process corresponding to one of the noises;

- number of independent interference sources.

The task of the receiver is to use the received corrupted signal to determine which message was transmitted. The set of receiver operations can be described by the operator relation:

(3.4)

Where - receive method operator;

- demodulation operator;

- decoding operator;

- a random process of occurrence of failures and failures in the receiver.

The completeness of the correspondence of the transmitted sequence depends not only on the corrective capabilities of the coded sequence, the level of the signal and interference and their statistics, the properties of the decoding devices, but also on the ability of the digital system to correct errors caused by hardware failures and failures of the transmitter and receiver and . The considered approach makes it possible to describe the process of information transfer by a mathematical model, which makes it possible to identify the influence of various factors on the efficiency of digital systems and outline ways to improve their reliability.

It is known that all digital systems are unrecoverable and recoverable. The main criterion for the reliability of a non-recoverable digital system is the probability of failure-free operation:

(3.5)

is the probability that no failure will occur in a given time interval t; Where -

l - failure rate;

- the number of elements in the digital system;

- failure rate of one element of the digital system.

The main criterion for the reliability of recoverable digital systems is the availability factor

, (3.6)

which characterizes the probability that the system will be in good condition at an arbitrarily chosen point in time; Where - mean time to failure; This is the average value of the duration of continuous operation of the system between two failures.

, (3.7)

where N is the total number of failures;

- running time between () and failure.

.

- recovery time. Average system downtime caused by finding and fixing a failure.

, (3.8)

where is the failure duration.

where is the intensity of restoration, characterizes the number of restorations per unit of time.

3.2 Ways to improve the reliability of digital systems

Modern digital systems are complex geographically distributed technical complexes that perform important tasks for the timely and high-quality transmission of information.

Maintaining and providing the necessary repair and restoration work for complex digital systems is an important issue.

When choosing digital systems, you need to make sure that their manufacturers are ready to provide technical support during not only the warranty, but the entire service life, i.e. before reaching the limit state. Thus, when making a decision to purchase digital systems, operators need to take into account the long-term costs of its maintenance and repair.

It should be noted that the quality of the services offered, as well as the amount of costs incurred by the operator company in its activities, largely depends on the preparation and organization of the process of maintenance and repair of digital systems. Therefore, the task of improving the methods of maintenance and repair of geographically distributed digital systems is becoming increasingly important.

It is known that the requirements of international standards in the field of quality oblige the telecom operator as a service provider to include in the field of quality systems - maintenance and repair of digital systems.

As the international experience of developed countries shows, in which the period of mass digitalization of the telecommunications network and the introduction of fundamentally new services has already passed, this task is effectively solved by creating a developed infrastructure for organizational and technical support, which also includes a system of service centers and repair centers.

Therefore, suppliers of digital systems should organize service centers for warranty and post-warranty maintenance of their equipment, its current operation and repair.

Typically, the structure of the service center system includes:

the main service center, which coordinates the work of all other service centers and has the ability to perform the most complex types of work;

regional service centers;

telecom operator's technical service.

However, as practice shows, along with the high quality of the supplied equipment and its wide functionality There are also a number of problems:

insufficient development (and in some cases absence) of the service network for supplied digital systems;

there are more digital system providers than service centers;

high cost of repairing digital systems.

In this regard, suppliers must be subject to appropriate requirements for the organization of maintenance of the supplied equipment and the timing of the replacement of faulty components of digital systems.

Since the level of convenience of the maintenance functions of digital systems varies from system to system, working with different systems requires a different degree of training for maintenance personnel. As practice shows, telecommunication equipment suppliers build their strategy for organizing service support in different ways:

creation of the main service center of technical support;

creation of a developed network of regional support centers;

support through a network of distributors and a representative office;

support by the dealer network.

Currently, there is a wide variety of forms, methods and types of maintenance. Services to customers are provided in four different forms:

self-service by the customers themselves;

on-site service of the equipment;

service in centers that do not repair, but replace;

service in repair centers.

It should be especially noted that at present there is no single concept of service maintenance.

1. Some operator companies are of the opinion that the main task is to speed up repairs, which is achieved by replacing boards and even blocks, which then go through full cycle monitoring and restoring their performance in repair centers equipped with a set of modern diagnostic equipment.

2. Other operator companies prefer to move to element-level repairs, for which they use the latest diagnostic tools of high functional complexity to localize faults.

Therefore, an integral part of maintenance and repair systems as a system for managing the state of digital systems is a system of technical diagnostics. At present, it is generally recognized that one of the important ways to improve the operational reliability and, ultimately, the quality of the functioning of digital systems is to create an effective system of technical diagnostics.

Therefore, the solution of maintenance and repair tasks involves the use of an appropriate system for technical diagnostics of digital systems at the stage of their operation, which should provide a two-stage troubleshooting strategy in digital systems with a search depth, respectively, to a typical replacement element (TEZ), board and microcircuit. Taking into account the expansion of the range of digital systems, there is a need to reduce the requirements for the qualification of maintenance personnel of technical diagnostic systems, especially for service and repair centers. Diagnostic equipment intended for these centers should have, if possible, the minimum weight and size indicators and ensure that the specifics of each diagnostic object are taken into account.

Currently, the following main areas of work are known to improve the reliability of the functioning of digital systems:

1. First of all, reliability is enhanced by the use of highly reliable components. This direction is associated with significant costs and provides only a solution to the problem of reliability, but not maintainability. Unilateral orientation in the creation of systems to achieve high reliability (due to the use of a more advanced element base and assemblies) to the detriment of maintainability, in many cases does not ultimately lead to an increase in the availability factor in real operating conditions. This is due to the fact that even highly qualified specialists using traditional technical diagnostic tools spend up to 70-80% of active repair time searching for and localizing faults in complex modern digital systems.

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NEWS

TOMSK ORDER OF THE OCTOBER REVOLUTION AND THE ORDER OF LABOR RED BANNER POLYTECHNICAL INSTITUTE them. S. M. KIROVA

EFFICIENCY AND RELIABILITY OF HARDWARE CONTROL OF DIGITAL DEVICES

N. P. GANG

(Presented by the scientific seminar of the Department of Computer Science)

The most important indicators of the quality of hardware control circuits (AC) of digital devices (CC) - the effectiveness and reliability of "control" are not currently clearly defined. To clarify these concepts, let us consider a set of different states of the CC with AC (Table 1). At the same time, we will understand the effectiveness of control as the probability of detecting an error that has appeared in the

Table 1

Status Status Reaction

Monitored Circuit Monitored Circuit Monitored Event Note

A B C

H0 0 0 0 system bots

N, 0 0 1 Impossible event

H.J 0 1 1 1 Specifies Esam

H5 But 1 0 ] Defines Em

new scheme (OS). Such an efficiency criterion, in accordance with the terminology of the theory of operations research, most accurately reflects the goal of the control scheme (SC) - to detect the maximum number of possible errors in the OS, and therefore received the most distribution.

In table. 1 digit 0, depending on the column number, means the absence of errors in the OS (L), the control circuit (B) or the absence of an error signal at the output of the SC (C). Events R/ (r = 0.7) determine the states of the system (in this case, the system is understood as the totality of the main circuit and the AC circuit). For example, the R3 event means that the OS is healthy, and there is an error in the control scheme that is detected. Let's call the conditional probability P(C/AB) = E the self-efficacy of self-control, and P(C/AB) = Em - the effectiveness of the control method.

Analyzing the table. 1, we can say that the effectiveness of control as the probability of detecting an error that appeared in the OS is P (C / A),

is determined by the events R4 - H7. Using the probability multiplication theorem, we can write

P (C "A) \u003d P (AC) ... (1)

^■ "psh ^>

According to Table. 1

P(AC) - P(H:) + P(//7) = + (2)

Substituting (2) into (1) and taking into account that the events A and B are independent, and the event C depends on A and B, we obtain

P(ABC) + P(ABC)

P (AB) -P (C AB) + P (AB). P (C: AB)

P(B)-3M + P(B)-P(C¡AB).

It follows that the effectiveness of control is determined by the effectiveness of the control method, the probability of error-free operation of the control circuit and the probability of detecting multiple errors that appear simultaneously in the main and control equipment.

When analyzing the reliability of AC, it is advisable to consider two criteria.

1. D] = P(A/C) - the reliability of a positive result of the control (the probability of faults in the OS, if there is an error signal at the output of the SC). Here and below, a malfunction is understood as a failure or failure of an arbitrary multiplicity. Moreover, it is assumed that the malfunction determines an error of the same multiplicity.

2. JXq = P(Á/C) - the reliability of the negative result of the control (the probability of the absence of faults in the OS, if there is no error signal at the output of the SC.).

By the Bayes formula, we have

D R (L "S) R (A) -R (CA)

1 P(A)-P(C:A) + P(A)-P(C!A)

R (A)-R (CIA)

P(A)-P(C;A) + P(A) \ 1 -P(C A)]

" P (A) -E -f P (A) - P (Á-P (CÍÁ)

The conditional probability Р(С/А) is the probability that the signal at the output of the SC will not appear if there are no faults in the OS. By analogy with formulas (1-3), we can write

P (C: A) \u003d \u003d P SV) + p (B) (1 - Esam). (5)

Hence it follows that in order to increase the probability P(C/A) it is necessary to increase the probability of proper operation of the SC and reduce the "negative" effect of self-control efficiency. The latter can be achieved by introducing diagnostic tests that distinguish between faults that appear in the main and control equipment. Then in (5) it is necessary to consider instead of ^ itself

ESam = Esam.Ks, (6)

where Kc is a coefficient showing what percentage of errors in the control circuit causes the signal "system failure" to appear (Fig. 1).

The reliability of a negative control result is determined similarly to O! _ __

R (A) ■ R (C/A)

B0 = P(L/S) =

° (A) -P (C / A) + P (A) - P (A) - E

koytro / yu shtoo / yu

Osh/ghtst operation

System failure / Schema failure hot o o / o

Rice. 1. Block diagram of the system

If AC allows not only detecting, but also correcting errors, then an additional efficiency criterion must be taken into account - the probability of correcting an error that has appeared in the OS (Ep). This "criterion can also be calculated by formula (3), understanding by Em and P(C/AB) the corresponding error correction probabilities.

1. The analysis of the most important indicators of the quality of hardware control circuits of digital devices was carried out: the effectiveness and reliability of control.

2. As a result of the analysis, two efficiency criteria were selected: the probability of detecting and the probability of correcting an error that appeared in the main scheme, and two reliability criteria: the reliability of positive and negative control results.

3. Based on the consideration of the state table of the CC with AC, formulas are derived for calculating the indicated criteria for the effectiveness and reliability of control at the early stages of system design.

LITERATURE

!. "Fundamentals of designing control machines for industrial use". Ed. B. N. Malinovsky. "Engineering", 1969.

2. A. M. Sidorov. Control methods for electronic digital machines. M., "Soviet radio", 1966.

3. E. Ya. Peterson, N. D. Putintsev. Criteria for evaluating the effectiveness of the computer control system to ensure the reliability of the output information. - "Automation and computer technology", 1968, No. 3.

4. E. Ya. Peterson, N. D. Putintsev. Choice of parameters of control schemes in the paths of control computers. Izv. Academy of Sciences of the USSR. "Those. Cybernetics", 1969, No. 5.

5. V. N. Verigin. The main characteristics of hardware control with error detection in relation to the digital computer, ITM and CT of the Academy of Sciences of the USSR. M., 1966.

6. N. D. Putintsev. Hardware control of control digital computers. M., "Soviet radio". 1966.

7. Yu, G. Zaiko. To the calculation of the effectiveness of control modulo. - "Cybernetics", 1967, No. 6.

8. G. N. Ushakova. Hardware control and reliability of specialized computers. M., "Soviet radio", 1969.

9. N. P. Baida, V. M. Razin, and V. M. Tanaseychuk, “On the Calculation of the Efficiency of the Hardware Control System of Electronic Digital Computers,” At. XXV All-Union scientific session dedicated to Radio Day and Signalman Day. (Abstracts and abstracts of reports). M., 1969.

10. N. P. Baida, V. M. Razin, and V. M. Tanaseychuk, On the Question of the Optimum Choice of the Efficiency of a Computer Hardware and Test Control System by the Calculation Reliability Criterion. II All-Union Conference on Technical Cybernetics. (Abstracts and abstracts of reports). M., 1969.

11. V. I. Perov and T. D. Zhol carpet. Evaluation methods and some ways to improve the reliability of the results of automatic control. Automatic control and methods of electrical measurements. Proceedings of the V conference. T. 2, Novosibirsk, 1966.

12. E. S. V e n t c e l . Introduction to operations research. M., "Soviet radio", 1964.