Circuit for monitoring the mechanical power from an induction motor and for detecting excessive heat exchanger icing

摘要

An electronic signal proportional to Icos theta for an induction motor is substantially proportional to the mechanical power output of the motor. This signal is detected by rectifying a signal which is an analog of motor current in phase with the motor voltage and time averaging the rectified signal. Comparing the averaged signal to a reference level permits the interruption of motor current for an underload or an overload condition. The circuit permits detection of excessive ice formation on the outdoor heat exchanger of a heat pump system. The circuit is connected to the impeller drive motor which forces air across the heat exchanger and stops the motor and initiates the de-ice procedure when the ice blockage causes mechanical power delivered by the motor to deviate to a selected level.