Floating-type electronic servo-motor process controller

TLDR: In this article, a floating-type electronic process controller including a differential amplifier is used to produce a deviation signal whose polarity and magnitude reflect the direction and extent of the departure of the process variable from the set point.

Abstract: A floating-type electronic process controller including a differential amplifier which compares a voltage proportional to a process variable with a set point voltage to produce a deviation signal whose polarity and magnitude reflect the direction and extent of the departure of the process variable from the set point. The deviation signal is converted into on-off signals by applying it to a pair of comparator channels to which are also applied a triangular reference voltage having a constant frequency. When the deviation signal reflects a process variable which is below the set point, one channel is activated to yield square-wave pulses whose rate corresponds to the frequency of the reference voltage and whose pulse duration is proportional to the magnitude of the deviation signal, but when the deviation signal reflects a process variable which is above the set point, the other channel is activated to provide similar square-wave pulses. The square-wave pulses serve to trigger the triac control circuit of a reversible motor operatively coupled to a final control element, the pulses from one channel causing the motor to turn in one direction and the pulses from the other channel causing the motor to turn in the other direction, the duty cycle of the motor being determined by the duration of the pulses.