Electronic Design

Pneumatic Logic Devices Pushed

Pressed by the need for computing systems able to operate in extreme environments and in industrial control applications with high efficiency, designers are pushing development of pneumatic and hydraulic logical devices. Advantages claimed for pneumatic and hydraulic logic elements are their ability to pack a lot of computational capacity into a small volume, their resistance to extremes of temperature and radiation, and their low manufacturing cost. Their disadvantages are the unfamiliarity of their technology to electronic designers who would have to work with or design them, and their relatively low speed. Clock rates of 10 to 100 kc appear to be feasible, depending on operating pressures needed. For many industrial control applications, and some computing functions, this speed is adequate.

So far, developments have been announced by Diamond Ordnance Fuze Laboratories, Washington, D.C., Moore Products Co., Philadelphia, Minneapolis-Honeywell Regulator Co., Minneapolis, Kearfott Div., General Precision Inc., Little Falls, N.J., and IBM, Yorktown Heights, N.Y. Researchers in the Soviet Union also are known to be well along in development of pneumatic and hydraulic logic systems.

In the systems under development, either a gas or fluid is made to flow through a network of channels and orifices in such a way that differences in pressure give solutions to logical problems. In some potential applications, the gas or fluid pressure would do actual work, like moving parts.

Two approaches are being pursued. At DOFL, Moore Products, and Minneapolis-Honeywell, circuit elements with no moving parts are under development. Kearfott is building pneumatic elements, and IBM is making hydraulic elements, in which moving parts aid circuit operation and simplify connection of the components to electrical systems. The photo shows a scale-of-two counter, built at IBM's Zurich laboratories, which has four stable states, operating hydraulically with moving sleeve valves.

In 1959, DOFL scientists built analog fluid amplifiers that provided substantial gain. They have since built digital amplifiers and flip-flops, added feedback to their units, and built oscillators and counters. (Electronic Design, May 24, 1961, p. 4)

The basic pneumatic logic element, a flip-flop, had two stable states. It operated with one input port and two outputs. In one type, small control pulses of air directed the incoming gas stream to one of the outputs to indicate a "1" or a "0." The gas flow continued through that port, even after removing the control pulse. In another type of device, a ball was shuttled between the two outputs to block the air stream through one port, representing a "1" or a "0." The devices continued under development into the mid-1960s and were deployed in some industrial systems, but interest faded as digital ICs came online.

See associated figure

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