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(also, pneumonics), a branch of pneumatic automation that deals with the study, development, and use of devices (elements) that operate on the basis of aerohydrodynamic effects, such as momentum interaction, wall attachment (or wall reattachment), creation of turbulence of the stream in a laminar jet, throttling of flows, and vortex generation.
In discrete momentum-interaction elements, the jets flowing out of the input channels deflect other jets coming from the supply channel or from other input channels; in this case the pressure and delivery of air at the output of the element vary according to the relay characteristic. In wall-attachment elements, the properties of boundary-layer flows are used to produce and signal storage. In turbulence elements a relay characteristic is produced by the transition from laminar to turbulent flow. Various aerohydrodynamic effects are used in continuous-operation fluidic elements. The functions of the controllable throttles (flow-type pneumatic resistances) that create pressure gradients in streams are performed by vortex jet elements in which the output pressure is varied by making the flow turbulent with a jet emerging from a control channel.
The elements and devices of fluidics are made mostly from plastics by investment casting, compression molding, or photochemical etching methods that create depressions on the surfaces of flat plates to form the jet elements and communication channels. When such plates are covered with caps having orifices for the admission and removal of air (supply; input and output signals), the results are finished fluidic devices.
Jet elements of various types are used in low-pressure fluidic systems, with excess input and output pressures of about 0.1–1 kilonewton per sq m (kN/m2), and in combined jet-diaphragm automatic systems, where the maximum standard pressures of the input and output signals in the system are about 100 kN/m2.
Fluidic devices use active elements, which have input, output, and supply channels, and passive elements, which have no supply channel. They are supplied from compressors, compressed-air cylinders, or centralized systems into which air is forced by a compressor. To ensure trouble-free operation of fluidic devices when the air contains dust, a semiclosed supply system is used (part of the air from the outputs of the pneumatic elements is returned to the supply channels) and a low excess pressure is generated in the area where the elements are located, thus inhibiting the penetration of dust particles from without.
Fluidic devices are used in industrial automatic control systems to perform various logic functions and in systems that include digital counters, shift registers, and units for the bit-by-bit comparison of numbers. Such devices are used to perform not only discrete operations, such as summing of signals and bit-by-bit comparison of codes, but also analog operations, such as conversion, amplification, and frequency modulation of signals.
Devices are constructed with fluidic elements that measure the input parameters of automatic systems, such as flow velocity, flow rate, absolute gas pressure, pressure ratios, temperature, time, linear dimensions, rate of rotation, acceleration, forces, torques, and certain magnetic and electrical quantities. Fluidic elements are used in industrial controllers, in indicators of gas concentration and the position of objects, and in other devices designed for automation of processes in the petroleum-refining, gas, and chemical industries and in machine building. Fluidic elements and devices have been developed for control systems of power installations, agricultural equipment, and transportation. Such devices function normally at high and low temperatures, are fireproof and explosion-proof, are not affected by inertial overloads and vibrations, and are not subject to radiation effects. Therefore, they are used in aviation, rocketry, and space technology and in nuclear power engineering. Fluidic elements are used in medical equipment, such as the control systems of apparatus for assisted circulation and artificial respiration.
The basic elements of fluidics are designed to operate with low power consumption, usually about 10–2 watt; jet switches analogous to such elements are made for powerful gas streams to control ventilating systems, to improve smoke-trapping processes in factory smokestacks, and to control the thrust of jet aircraft engines. Devices have been developed for hydraulic-jet engineering based on the same principles as fluidic devices.
The USSR was the pioneer in the development of fluidics. Many other countries are now developing and studying fluidic elements and devices.
REFERENCESZalmanzon, L. A. Teoriia elementov pnevmoniki. Moscow, 1969.
Zalmanzon, L. A. Aerogidrodinamicheskie metody izmereniia vkhodnykh parametros avtomaticheskikh sistem. Moscow, 1973.
Elementy i ustroistva pnevmoavtomatiki nizkogo davleniia (struinoi tekhnikf): Katalog-spravochnik. Moscow, 1973.
Agregatnoe postroenie pnevmaticheskikh sistem upravleniia. Moscow, 1973.
Foster, K., and G. A. Parker. Fluidics: Components and Circuits. London, 1970.
L. A. ZALMANZON