Integral controller for carrier-type servomechanisms

SATISFACTORY integral controllers and integrators for use in d-c servo systems and computers now exist. Unfortunately good counterparts do not exist for use in a-c servo systems and computers. Band-pass filters may be used, but they are unsatisfactory if the carrier frequency changes. The usual integral controller consists of a phase-sensitive detector which converts the a-c input signal into a direct voltage. This direct voltage is applied to a d-c integral controller and the output of this controller is remodulated. Often drifts of the detector and modulator of this last system introduce more error than is desirable.