Method of closed-loop digital control

Between large complex digital-computer control systems and simple analogue process-control loops lies an area in which relatively simple digital electronic controllers are needed. The device described in the paper consists of a pulse-repetition-rate sensing device, a controller working on mathematical principles (which are analysed in some detail in the paper) and an output device which converts the correction signal into pneumatic form for use with conventional pneumatic positioning-control valves. The results of laboratory tests are also reported, and the unit is now undergoing field trials and further development.