Pneumatic Automation

the set of devices for the construction of automatic control systems in which the information is represented by the pressure or discharge of a gas, usually air (pneumatic signals); the branch of engineering that studies this form of automation. Pneumatic automation uses devices for collecting information (transducers with pneumatic output, pneumatic limit and travel switches, and so on), for conversion and storage of information (pneumatic controllers, optimizers, analog computer devices, and relay systems), for data display (indicating and recording devices and display units), and for conversion of data into control actions (pneumatic final-control elements).

Because of its low speed of response, pneumoautomatic hardware is used in control systems for slow processes and in cases where performance of a very large number of computations is not necessary for execution of a control algorithm. In spite of these limitations the field of application of pneumoautomatic hardware is very broad. In particular, it is used in most control systems for production processes. Pneumatic methods of automation are often given preference over electronic methods. This is mainly because pneumatic equipment is by nature explosion-proof and fireproof and, in addition, is better suited to operation under industrial production conditions, particularly if the air in production areas is badly polluted or if the production processes generate strong electromagnetic fields. It is the prinicipal method of automation in the chemical and petroleum-refining industries; in petroleum, gas, and coal-extraction enterprises; and in the transportation of petroleum and gas.

Pneumatic devices for the stabilization of a single parameter have become the most common in solving automation problems. Such devices combine a transducer, a master device (setter), a controller, and the indicating and recording instruments—that is, all the instruments that make up a single-loop control circuit. However, in machine building simple discrete automation systems have often been constructed by combining limit and travel types of pneumatic switches and distributors for pneumatic actuating mechanisms in a relay system.

An important step on the path toward the creation of an integrated system of general-purpose pneumoautomatic control devices took place in the early 1950’s with the shift to integrated construction of a control systems, which is accomplished by means of a set of functional modules and instruments. In the USSR such a system of devices has been designated as the unified integrated system. Its use has substantially broadened the potential of pneumatic automation in the construction of control systems for continuous production processes.

The development and use in pneumatic automation of all-purpose elements led to a dramatic change in the potential of such automatic control. A system of pneumatic elements called USEPPA (universal system of elements for industrial pneumatic automation) was developed and put into production in the USSR during the early 1960’s. Since then the element (modular) method of constructing pneumatic control systems has become the practice. USEPPA has become the basis for the production of the Start system, a new set of standard devices that replaces and overlaps the unified integrated system in its functional potential, and the Tsentr system, an integrated set of devices for the centralized monitoring and control of numerous continuous production processes. Both systems completely meet the requirements for pneumatic automation.

Discrete control systems are constructed from elements of USEPPA. As a result of the development of relay engineering, modern pneumatic automation differs little from modern electronic automatic control in both functional potential and structural features. This is most evident in the Tsikl set of pneumatic devices, which is designed for the control systems of periodic (cyclical) processes. The elements of the set are based on jet-diaphragm relay devices. The basic component of the set is the subunit, which is a board with a pneumatic printed circuit that carries the set of pneumatic elements (jet modules and diaphragm amplifiers) belonging to the subunit. The system includes a set of subunits that perform various functions; virtually any control system of the cyclical type can be constructed from such a set. The subunits of the system are coupled by means of special pneumatic connectors in containers that form the units; several units, in turn, are mounted in standard cabinets, bays, and consoles.