Telemechanics


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Telemechanics

 

(Russian, telemekhanika), the area of science and technology concerned with methods and equipment for transmitting and receiving information (signals) for the purpose of control and monitoring at a distance. The English term “remote control” in its broadest sense has a similar meaning. Such examples of remote control as telephone and television systems, however, are not regarded, in Russian usage, as pertaining to telemechanics.

In Russian usage, telemechanics differs in a number of features from other areas of science and technology—for example, telephony, telegraphy, and television—that deal with the transmission of information over a distance. The most important of these features are the following: the transmission of very slowly changing data, the need for an accuracy of transmission of the measured quantities as high as 0.1 percent, the impermissibility of a sizable delay in the transmission of the signals, a high reliability of transmission of control commands (the probability of the occurrence of a false command must not exceed 10–6–10–9), a high degree of automation of the processes of data collection and use (telemechanics permits of human participation in data transmission only at one end of the transmission channel), and the centralization of information processing. These features stem from the specific nature of the problems solved by telemechanic means.

Telemechanic methods are generally employed when it is necessary or advisable to join unconnected or territorially dispersed controlled systems into a single complex—for example, in the control of a gas or oil pipeline, a power system, a railroad terminal, or a network of meteorological stations. Telemechanic techniques are also employed when the presence of a person at the controlled system is undesirable for health reasons—as in the atomic energy industry or in some chemical plants—or is impossible because of the inaccessibility of the controlled system—as in the control of an unmanned rocket or moon rover.

Methods and equipment. Any control process includes control proper—that is, the exertion of an influence on a system for the purpose of changing its state, for example, its position in space or the values of its parameters—and monitoring of the state of the system. Control and monitoring by telemechanic means are usually carried out from a control center, where the operator is located. The controlled systems may be concentrated in one place —that is, at one controlled point—or may be scattered—that is, located individually or in groups over a large territory or in a large space. The distance between the controlled point and the control center may range from a few tens of meters, as in the control of a construction crane, to tens or hundreds of thousands of kilometers, as in the control of an unmanned space probe.

Telemechanic information may be transmitted through specially designated wire or cable communication lines, radio channels, electric distribution systems, power transmission lines, or channels of an optical, hydraulic, or acoustic nature. In addition, telemechanic information is sometimes transmitted through channels intended for the transmission of other signals, for example, telephone channels or data transmission channels. In this case, a certain frequency band of the channel or an entirely unoccupied telephone or telegraph channel is set aside for the telemechanic signals. Control information can be transmitted to tens or even hundreds of controlled points by a single standard telephone channel. When special wire lines are used, the equipment at the controlled points is usually connected in parallel to a common line whose structure may be quite complicated; the structure may be treelike, ring-shaped, or bushlike in form or may be of a mixed nature. Series connection of the communication lines and the equipment of an individual controlled point is used much less often because of the low reliability of such connection. If radio channels are used to transmit telemechanic information, we speak of radio control (see).

The aggregate of the devices used by a human operator to control systems and monitor their states at a distance is called a telemechanic system (in English, such a system would generally be called a remote-control system). In Russian, a distinction is made between telemechanic systems that perform only control functions and telemechanic systems that perform only monitoring functions. The former are called remote-control systems (sistemy teleupravleniia), and the latter are called remote-monitoring systems (sistemy telekontrolia). The term “remote-control system” is used below in this narrow, Russian sense.

The control actions in a telemechanic system may be generated in part by an automatic control unit. Such a unit may, for example, automatically shut off equipment in the event of an emergency, connect loads to a power system, or control devices according to a preassigned program. In the remote control of complex systems, electronic computers are used to process the monitoring information obtained. The computers function as “advisers.” Such telemechanic systems are called computer-aided systems. Telemechanic systems in which the control actions are generated entirely automatically are referred to as automatic systems.

In remote control, control commands are transmitted by the operator from the control center through a communication channel to the controlled systems or controlled points. The operator initiates commands at the control console by means of manual switching devices, such as toggle, selector, and push-button switches. A coded signal, usually in the form of a pulse train with certain characteristics (seeCODE), goes from the control center to the communication line. Because of the necessity of ensuring high reliability in the transmission of control commands, remote control makes use of special coding methods and methods of error detection and correction involving positive signal acknowledgement, that is, the repetition of signals through a return channel. When it is received, the coded message is converted into a control action applied to the appropriate actuating mechanism, a simple example of which is a relay that switches on a motor.

In remote monitoring, information is transmitted in the reverse direction—that is, from the controlled system or point to the operator at the control center. Monitoring information on the state of the controlled system is usually received from transducers, or sensors, that react to changes in the parameters of the controlled system. To make the transmission of such information easier, coding and modulation, or modulation alone, are used; the modulation may involve double or triple modulation—for example, double frequency modulation or pulse-duration modulation followed by frequency modulation. At the control center, after demodulation and decoding, indicators give the value of the parameter being measured or present the change in the state or position of the controlled system.

The messages transmitted by remote-monitoring systems usually contain two types of information, which may be called signaling information and measurement information. Signaling information gives a qualitative assessment of the state, or condition, of (1) individual control elements, which may be described as being, for example, on, off, or open; (2) the controlled system as a whole, which may be described as, for example, idling, moving, or being up or down; and (3) parameters characterizing the controlled system, whose values may be, for example, normal, below normal, above normal, or at an emergency level. Measurement information gives a quantitative evaluation of the monitored parameter, which may be, for example, temperature, pressure, the voltage in an electric circuit, or a shaft rotation angle. The remote-monitoring process corresponding to the transmission of signaling information is called remote signaling (telesignalizatsiia), and the remote-monitoring process corresponding to the transmission of measurement information is called telemetering.

In Russian, a distinction is made between, on the one hand, remote control and remote monitoring and, on the other hand, what may be called distance control (distantsionnoi upravlenie) and distance monitoring (distantsionnyi kontrol’). In remote control and remote monitoring, all signals are generally transmitted through a single communication line. Multiwire telemechanic systems do exist, but the number of wires in them is much smaller than the number of systems being controlled or monitored. This characteristic of telemechanics permits information to be transmitted over a distance with smaller material expenditures than in distance control.

Most controlled systems are two-position in nature—that is, they can be in one of two states (positions), for example, on or off. Examples are electric motors, luminaires, and railroad switches. The control commands therefore are generally discrete in character, for example, on-off or start-stop. Sometimes, however, the controlled parameter must be varied smoothly. In this case, the operator sends continuous control signals and coordinates his subsequent actions with the measurement information received from the controlled system. This type of remote control is called remote regulation (teleregulirovanie).

For precise and reliable performance by the operator, the information transmitted and received must be represented in a form convenient for human perception. For this purpose, various types of warning devices, indicators, and automatic recording devices are used at the control center.

To ensure the independent transmission (and reception) of many signals over a single communication channel in telemechanics, the signals are separated so that they retain their individual properties and do not distort each other. Of the many existing methods of signal separation (seeMULTICHANNEL COMMUNICATION), telemechanics usually employs the following: time division (some time interval is allotted to each controlled system), frequency division (a frequency band is assigned to each controlled system), a combination of frequency and time division (for example, frequency division for the controlled points and time division for the systems at a single controlled point), and address assignment (an address is assigned to each controlled point, and all messages must begin with the address of the controlled point selected).

The theory of telemechanics studies the shaping and conversion of telemechanic signals, the transmission of such signals over communication lines with a limited frequency passband and in the presence of noise, the presentation of information to the operator, and the methods and equipment involved in the realization of telemechanic systems. The main problems confronting telemechanics include the improvement of the reliability of data transmission, the efficient use of communication channels, and the development of economical and reliable equipment.

History and areas of application. The first attempts at carrying out measurements and controlling the operation of machines at a distance were made in the late 19th century. The term télécommande was proposed in 1905 by the French scientist E. Branley. Originally, the concept of telemechanics was associated with the radio control of military vehicles. In a few cases in World War I military equipment was provided with devices for control at a distance. The practical application of telemechanics for peaceful purposes began in the 1920’s, chiefly in rail transport. The remote control of railroad signals and switches was first accomplished in 1927 in Ohio on a stretch of track 65 km long.

The world’s first radiosonde with telemetering equipment was launched in the USSR in 1930. In 1933 the first remote-signaling device was introduced in the Moscow Power System. The practical application of telemechanic equipment in the Moscow, Leningrad, and Donbas power systems dates from 1935 and 1936. Remote control of switches and signals was implemented on the Moscow-Riazan’ Railroad in 1935. In the early 1940’s centralized remote control of street lighting was introduced in Moscow. The factory production of telemechanic equipment on a lot basis began in the USSR in 1950 at the Elektropul’t Plant. By 1955 a trend toward the reequipping of telemechanic facilities had taken shape. The replacement of unreliable relay-contact elements by semiconductor and magnetic noncontact elements began throughout the country in 1958. The first electronic telemetering system in the USSR was developed in 1955 and 1956. The late 1960’s and early 1970’s saw the introduction of integrated circuits in the equipment of telemechanic systems.

Each year the use of telemechanic systems in the USSR increases. Such systems are employed, for example, in the chemical, atomic, metallurgical, and mining industries; at electric power plants and substations; at pumping and compressor stations associated with oil and gas pipelines and with irrigation and water-supply systems; at railroad terminals and airports; in amplification and relay equipment of communication lines; and in warning systems. In the 1930’s, the use of telemechanic systems in the USSR was limited to a few tens of instances. The number reached a few tens of thousands in the 1950’s and exceeded 500,000 in the mid-1970’s. By 1975, more than 5,000 telemechanic systems were in operation in Soviet power systems, about 40,000 km of railroads had been equipped with telemechanic systems, and telemechanically operated wells accounted for more than 80 percent of the country’s petroleum production. The introduction of telemechanic systems permits a reduction in maintenance personnel, decreases equipment idle time, and frees man from work under hazardous conditions. Telemechanics is taking on particular importance in connection with the development of automatic control systems.

Telemechanic systems in use in the USSR in 1976 included the following: the MKT, Stimul, TM-500, TM-511, and TM-512 (for remote control of power-generating units at power plants and industrial enterprises and for the control of power systems and power grids); the TM-100, TM-120–1, TM-600, and TM-625 (for centralized remote control of gas and oil pipelines, power transmission lines, and various oil-field and transportation systems); the TM-300, TM-310, and TM-320 (for industrial enterprises); the EST-62 and Lisna (for equipment in railroad power-supply systems); and the ChDTs and Niva (for railroad traffic control).

Outside the USSR, considerable effort is being expended on the development and introduction of a variety of telemechanic systems and of information systems with telemechanic equipment. Telemechanic systems in use in France include the Marathon IV, TMSS, TT-40, TT-3000, Redeka, Teleconta, Consip, and Telesil. Examples of systems used in Switzerland are the DASA, Telegyr 505, Telegyr 707, ZUT, DFM, and DUFA. Belgian systems include the Digitel 140, Digitel 1000, and TS-SL. In the Federal Republic of Germany, the Geatrans (F-101, F-102, and F-200) and EFD are in use. Systems employed in Great Britain include the DT-3, Teleplex, and Serck. Italian systems include the TLSM-30, P-6006, and STO-3400. Some examples of systems used in the USA are the Bristol, DS-3500, System-9000, and Datelok-7.

Telemechanics plays a very important role in the exploration of space. The use of telemechanics is an essential condition for the successful launching of artificial earth satellites, manned spaceships, unmanned interplanetary probes, and lunar probes. Telemechanic devices transmit from spacecraft to control centers data on the operation of onboard systems and essential measurement information, including data on the health of astronauts (seeBIOTELEMETRY). The control of space vehicles from the earth is accomplished by telemechanic means. The terms “radio control” and “radiotelemetry” are sometimes applied to remote control and telemetry with respect to aviation, rocket technology, and space vehicles.

REFERENCES

Shastova, G. A. Kodirovanie i pomekhoustoichivost’ peredachi telemekhanicheskoi informatsii. Moscow-Leningrad, 1966.
Beskontaktnye elementy promyshlennoi telemekhaniki. Moscow, 1973.
Tutevich, V. N. Telemekhanika. Moscow, 1973.
Il’in, V. A. Teleupravlenie i teleizmerenie, 2nd ed. Moscow, 1974.
Makarov, V. A. Teoreticheskie osnovy telemekhaniki. Leningrad, 1974.
Fremke, A. V. Teleizmereniia, 2nd ed. Moscow, 1975.

G. A. SHASTOVA

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