Overload sensing circuit for a motor

摘要

An overload-sensing circuit for an electric motor driven by an alternating signal comprises a supply line connecting the motor to a power source, a resistance in the supply line, and a first comparator for measuring the phase relationship between the power source voltage signal and the motor current signal. A variable resistor is employed to select a phase relationship which represents a load limit for the motor. A second comparator compares the measured phase relationship to the selected phase relationship and produces a signal representing an overload condition of the motor when the measured phase relationship generally equals the selected phase relationship.