Johnson Service Company

David W Jiral

David P DeBoer

A proportional plus integral controller operates an actuator in an HVAC system. The controller includes a setpoint circuit for providing a setpoint signal representative of a desired room temperature, a sensor circuit for providing a sensor signal representative of the actual room temperature, an error generator for generating an error signal proportional to the difference between the setpoint signal and the sensor signal, and an integrator for generating a control signal related to the time integral of the error signal. The setpoint and sensor signals are derived from a common voltage reference, so that accuracy of the controller is substantially independent of fluctuations of that reference. The integrator includes a capacitance multiplier that provides highly accurate integration of the error signal and a switch for selecting either proportional plus integral or proportional only control. The controller includes an integration disable circuit that removes the integral term from the control signal when the proportional component becomes large enough to fully drive the actuator. The controller also includes a mode selector to configure the controller to operate in either a heating or cooling mode.

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Huntington, IN, United States of America

David W Jiral