METHOD OF OPTIMIZATION AND PROTECTION OF DIAGNOSTIC DATA IN MONITORING RAILWAY AUTOMATION DEVICES

ABSTRACT

Works on the logical processing of control and diagnostic data in devices and systems of railway automation and telemechanics have been studied and their shortcomings have been identified. On the basis of these shortcomings, and as an addition to them, the possible modes of operation of the supply transformer, which is one of the automation and telemechanics devices that can be controlled during operation at signal points of automatic blocking, are investigated. For the tasks of technical diagnostics of this device, the current limits were determined and divided into ranges by significant values. In order to increase the efficiency of logical processing and sending diagnostic data via communication channels, the information vectors obtained during the measurement are replaced by the principle of quantizing the range of values, depending on the correspondence of these ranges to vectors with a small length. As a result, it was possible to reduce the load on the computing device when performing logical and arithmetic operations and reduce the time required for this. In addition, issues of protecting simplified data packets when they are sent over a communication channel were considered. For this purpose, cyclic codes are used, depending on various generator polynomials, to check for the presence of distortions in data transmission. Based on the results of a comparative analysis of the results of errors that cannot be detected when checking the data for errors of the codes used, recommendations and conclusions on the use of cyclic codes are given, depending on various generating polynomials.

АННОТАЦИЯ

Исследованы работы по логической обработке данных управления и диагностики в устройствах и системах железнодорожной автоматики и телемеханики и выявлены их недостатки. На основании этих недостатков, и как дополнение к ним, исследованы возможные режимы работы питающего трансформатора, являющегося одним из устройств автоматики и телемеханики, которые могут контролироваться в процессе эксплуатации на сигнальных точках автоблокировки. Для задач технического диагностирования данного устройства были определены пределы тока и разбиты на диапазоны по значимым величинам. С целью повышения эффективности логической обработки и отправки диагностических данных по каналам связи, информационные векторы, полученные при измерении, заменены принципом квантования диапазона значений в зависимости от соответствия этих диапазонов до векторов с небольшой длиной. В результате удалось снизить нагрузку на вычислительное устройство при выполнении логических и арифметических операций и сократить необходимое для этого время. Кроме того, были рассмотрены вопросы защиты упрощенных пакетов данных при их отправке по каналу связи. Для этой цели используются циклические коды, зависящие от различных порождающих полиномов, для проверки на наличие искажений при передаче данных. По результатам сравнительного анализа результаты ошибок, которые не могут быть обнаружены при проверке данных на ошибки используемых кодов, изображаются на графике в виде кривых. На основании этого графика даются рекомендации и выводы по применению циклических кодов, зависящие от различных порождающих полиномов.

Keywords: technical diagnostics of automatic blocking devices, monitoring, logical processing of diagnostic data, signal quantization, data protection, CRC codes.

Ключевые слова: техническое диагностирование устройств автоблокировки, мониторинг, логическая обработка диагностических данных, квантование сигнала, защита информации, коды CRC.

I. Introduction

Railway automation and telemechanics systems are of great importance in ensuring the process of safe and continuous transportation of goods and passengers in railway transport [1-3]. Currently, there is a trend towards the introduction of railway automation and remote control systems based on digital devices, i.e. microprocessor and microelectronic components [1,4]. Due to the increase in the number of digital devices, the amount of digital information exchanged between them increases several times. At the same time, the need to ensure the integrity and reliability of this information has increased [5]. Errors in information occur as a result of interference in the transmission of information. Simply put, the information sent on the sender's side may not be in the form of the original information on the receiver's side after exposure to these interferences [6]. This, in turn, can cause abnormal situations in train traffic control systems.

Data integrity violations can occur due to the following situations:

• inversion (distortion of bit values) of bits as a result of external influences;
• change in the value of the information vector;
• changing the order of bits or groups of bits, etc.

Various methods are used to protect data from the effects of interference, such as those described above, and to prevent threats to the integrity of information [6]. They are often considered integrity methods based on cryptographic approaches, and the following tools are currently used:

• control of amounts;
• hash functions (CRC – Cyclic Redundancy Code);
• digital signatures.

The simplest way to check the integrity of data transmitted in digital form is the checksum method, in which the checksum of the message is calculated (some value that identifies digital information). The hash function check (CRC) is a more reliable method of digital data identification system. The essence of this method is to calculate the control value of the cyclic redundancy code (CRC) of the data [7].

Ii. Literature survey

Today, there is practically no area where digital data is not exchanged. In addition, the exchange of digital data between objects and facilities of the railway industry is being widely introduced. Currently, on the roads of the post-Soviet space, a number of systems and devices of railway automation, their components, are outdated and do not meet the requirements of the time due to the large amount of waste of energy and resources. In particular, on the example of railway automation and remote control systems, on most railway lines operated in the former CIS countries, centralization and blocking signaling systems are used, which were put into operation in the 60s of the last century [8-10]. The control by ferry devices located between the stations and sending the data received from them to the centralized control room were carried out mainly through auto-blocking systems and frequency dispatch control (FDC) [11]. Until now, the devices of this system have simply worked out their resource and are kept in a partially serviceable (operable) state due to the end of the operational period, wear and tear and lack of components to replace the failed device [12-13]. The level of technical diagnostics of the state of devices of this type of systems is low, that is, they cannot provide the exact location and cause of device failures in the process of diagnosing, and the narrowness of the system functions indicates that this is incompatible with the acceleration of transport processes today. The knowledge of the reliability and integrity of monitoring and diagnostic data in these systems also raises doubts [14-16]. Given the strategic importance of railway systems, there is a need to optimize and protect data transmission over communication channels to a centralized single dispatch server. With this in mind, it is important to create methods and mechanisms for transmitting information in local conditions using modern methods from devices located at the signaling stations of the FDC system. At the same time, it is important to use methods for verifying the validity of the above information when sending.

III. The degree of study of the problem

In [17–20], measurements were carried out using various controllers at some control points for railway automation and telemechanics systems, methods for logical processing of monitoring and diagnostic data were studied. In particular, in [17-19], the authors carried out research on estimating the time of requests for analog signals in diagnostic and control systems for station devices of railway automation and telemechanics. To conduct this study, the authors used Atmel AVR microcontrollers. Due to the low speed of these microcontrollers and limited functionality, the issue of logical processing of the values measured by the analog-to-digital converter (ADC) device was not considered.

In [20], the author describes methods for monitoring automation and telemechanics devices using programmable logic controllers, as well as methods for diagnosing the state of devices. As an example, the connection to new control points for technical diagnostics and device monitoring is shown. In [21], the author proposes the principle of quantization of the input voltage of a traveling relay used in railway automation and telemechanics systems, divided into levels according to the most important operating modes of the device.

IV. Purpose of the work

In the above works, it can be noted that some parameters of devices and systems are not taken into account, the parameters of which are also important for presenting the “general picture” of the technical condition of the diagnosed object. Also briefly considered is the reduction in the number of transmission errors based on the digital processing of diagnostic data received from control objects. At the same time, the work on measuring analog, discrete and other parameters of signal points located between railway stations is not an exception. Therefore, the main goal of this work is to further study the checkpoints of the diagnosed devices of railway automation and telemechanics for the implementation of predictive diagnostics tasks and the study of methods for protecting information during logical processing and transmission, the formation of shortened data vectors about the parameters of the diagnosed device.

V. Methodology

To analyze the measured parameters of devices, a large amount of data is transmitted to a computing device, that is, to an arithmetic logic unit, which is considered the "brain" of the controller, based on various algorithms. This creates a certain load on him when processing data and requires him a certain amount of time for this. Usually, to measure analog values using special controllers, several bytes are required, depending on the number of bits of the analog-to-digital converter (ADC) [22].

,                                                       (1)

where D is the number of measurement steps (number of analog signal measurement levels) of the ADC; N is the number of ADC bits.

The greater the number of ADC bits, the higher the accuracy of the measured analog value, and the greater the amount of information generated by the controller. In fact, the amount of such information may be redundant for the parameters of the device being measured, and in this case the information received will have a large redundant part. In addition, it takes a long time to transmit information with such a redundant part over a communication channel, and the intensity of transmissions increases. Also, when sending a large amount of data over a communication channel, consisting of several bytes with such a redundant part, the number of errors will be greater. Taking this into account, the author of [21] proposed a logical processing method based on signal quantization in order to optimize the placement of all this data in one information vector (packet). In this case, the limit values (critical points) of the parameters of a particular device are determined, in other words, the levels of analog values by which a specific state of the device can be assessed. These intervals of critical points form different ranges. It is intended to replace these ranges with a few bits of data. With this method, the change in the parameter of the controlled device is broken down into "cases" (a range of critical points), which can be between minimum and maximum values. Simplified coding is then applied to these ranges, a process that further speeds up and reduces logic processing time.

In the above work [21], the author proposed to reduce the length of the diagnostic data vector based on the quantization of the travel relay supply voltage range. It should be noted that since each track circuit has its own norms (standards), the above conventional analog values are only general principles for approaching the problem under consideration. The diagnostics of the track circuit is carried out not only with the help of the track circuit relay itself. In addition, it is necessary to take into account the parameters of the transformer device that supplies this rail circuit with mains voltage. Accordingly, they can be defined as short-circuit current I_kz, load operating current I_rn, maximum load operating current I_rnmax, minimum load operating current I_rnmin and no-load current I_xx.

Based on the foregoing, let's consider an example of quantizing the range of important values of the current of the supply transformer of a track circuit and the principle of replacing the measured values with information vectors of small length. On fig. 1 presents the basic principles of quantization of the supply current levels of the track circuit according to the main threshold values of the parameters. The figure conventionally shows the curve I(t) and the levels of current values in the main operating modes of the transformer. As noted above, when adjusting a track circuit, it is mainly operated on the basis of the levels of the current value of the transformer shown on the vertical scale of the figure in different operating modes. Therefore, in order to reduce the number of data bytes in the process of logical processing, the values generated at each quantization step and corresponding to the same transducer parameter range are combined. Thus, it is proposed to represent this range of data bytes (denoted by curly braces) as one short data vector. For example, in the figure, the current range between the critical points I_rnmax and I_rnmin is conditionally defined, where the transformer supplies the devices connected to it with a rated current based on their total load R_n. Therefore, at each ADC quantization step, all data bytes falling within this range are replaced by a short vector 010. The remaining ranges are combined according to the same principle, all their data bytes are replaced by vectors of small length.

Figure 1. Quantization (number of measurements per unit of time) of the current range by the levels of critical values of the currents of the supply transformer of the track circuit:

a) Division of rail circuit supply current levels into ranges according to the most important current levels; b) Formation of a short data vector by combining their values

The length of the created data vector can be different depending on the characteristics of the device being measured and its modes of operation, states, and other parameters. Also, there is no need to use a large number of measurement ranges for zoning the input voltage values of the travel relay according to its state. It suffices to use a vector with a length of only 3 bits [21]. The analog parameters of other devices are also represented by a data vector of the same length as in Figure 1. Thus, if we assume that the number of ADC bits is 12, the size of the measured data from each device is 12 bits, and the data size of 4 such devices is 48 bits. Instead of this 48-bit data, our example generates a 10-bit vector. By adding one more 8-bit data vector from 8 discrete device states to the resulting 10-bit vector, a common 18-bit data vector is created. A detailed description of the sequence of bits that make up the data vector is shown in Figure 2. By adding a control vector to this data vector, a common sending packet is formed.

Figure 2. Generated data vector during technical diagnostics of the track circuit

VI. Experimental results

To reduce the number of errors in the transmission of the data vector, various codes are used, in which, by shortening the above proposed method, high efficiency can be achieved both in transmission and in data processing. For example, CRC codes are currently widely used in various communication channels, industrial data exchange protocols, and data processing devices [23]. The error detection function of this type of code depends on the generator polynomial. Generating polynomials are divided into classes depending on the length of the vector. Among them, we single out several types related to the 5th class (the class of the polynomial means the number of control bits in the code vector). Let's introduce the designation of generating polynomials, for example, as P38, P47, P52, P56, P59, where the decimal digits are the equivalents of the binary coefficients of the algebraic representation of these polynomials. The algebraic representations of these polynomials are expressed as follows:

• P38 – x⁵+x²+x¹;
• P47 – x⁵+x³+x²+x¹+x⁰;
• P52 – x⁵+x⁴+x²;
• P56 – x⁵+x⁴+x³;
• P59 –  x⁵+x⁴+x³+x¹+x⁰.

For the selected polynomials, undetectable errors are calculated using formula (2) [23]:

,                                          (2)

where N is the number of undetectable errors; m is the length of the information vector;

k is the length of the control vector; l is the degree of the smallest term of the generating polynomial.

Having calculated the ratio of the number of undetectable errors Ni in each bit of this information vector to the total number of undetectable errors N in fractions λ=Ni/N, we present the following table 1.

Table 1.

The ratio of the number of errors to the number of errors not detected

Based on the results of Table 1, we can conclude that the best detecting characteristics from their class of generating polynomials are the polynomials P47 and P59. When using these polynomials when transmitting information vectors over communication channels (wireless, wired), the level of error detection is much lower than with others, which makes it possible to achieve reliable transmission of diagnostic data.

VII. Conclusion and future work

Based on the results of studying the tasks of monitoring and diagnosing devices and equipment located at automatic blocking signal points related to train traffic control systems on the stage, the following conclusions were drawn. It is possible to use the data vector length simplification method for logical processing of control and diagnostic data by performing analog measurements using the example of a rail circuit supply transformer from among the system devices. This will reduce the load on the arithmetic logic unit when performing operations and reduce the data processing time. In addition, when using the above method, the efficiency of sending processed data from communication channels increases. At the same time, to check for errors (failures) when sending data over communication channels, as well as to increase resistance to interference, according to the results of experiments conducted using various CRC codes, it is advisable to use polynomials containing free members.

Using the above method, it is possible to increase the efficiency of work not only in systems and devices of railway automation and telemechanics, but also in other industries for collecting, processing and transmitting data.

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