Floating-type electronic servo-motor process controller

Claim 1

A floating-type electronic process controller adapted to accept a process variable signal and to convert it to on-off signals for controlling the speed and direction of a reversible motor operatively coupled to a final control element which governs the process, said controller comprising: A. a differential amplifier responsive to the departure of the process variable signal from a set point to produce a deviation signal whose magnitude and polarity depend on the extent and direction of the departure from the set point, B. a pair of comparator channels, C. a triangular-wave generator producing a reference voltage having a predetermined frequency, D. first means coupled both to said differential amplifier producing said deviation signal and to said generator producing said reference voltage to apply the deviation signal and said reference voltage to one of said comparator channels to produce first square-wave pulses whose rate corresponds to the predetermined frequency of said reference voltage and whose duration is proportional to the degree that said deviation signal reflects a process variable which is above said set point, E. second means also coupled both to said differential amplifier and to said generator to apply the deviation signal and said reference voltage to the other of said comparator channels to produce second square-wave pulses at the same rate and with a duration proportional to the degree that said deviation signal reflects a process variable which is below said set point; F. a control circuit for said reversible motor coupled to said channels and responsive to said first and second square-wave pulses to effect intermittent operation of said motor in a direction determined by which pulses are present, and G. a derivative amplifier interposed between said differential amplifier and said first and second means to provide for action in the proportional mode.