A triple-action positioning controller using a magnetic modulator

This paper describes a process control of the triple-action positioning type; i.e., the control circuits provide variable proportioning, automatic reset, and rate actions to position a valve or other modulating device. The input or error signal is derived from a recording instrument of the null-balance type, which can be a potentiometer recorder operating from a thermocouple, a self-balancing resistance thermometer, or a pressure recorder operating from a strain-gage transducer.