Abstract: An apparatus for controlling a motor comprises an oscillator for providing a source of periodic signals, and a divider for converting the oscillator output into desired motor rotation frequency signals. A tachometer generates actual motor rotation frequency signals and a comparator compares the actual and desired motor rotation frequency signals and generates a rotation frequency error signal. The tachometer and the divider are coupled to the comparator. An SCR bridge controls motor rotation frequency. The comparator is coupled to the SCR bridge. An AND gate coupled to the source of periodic signals provides a counting gate during which periodic signals from any suitable source are to be counted and a counter coupled to the AND gate counts the periodic signals. A display displays the number of such periodic signals counted during the counting gate.

Abstract: A speed-control system for an electric motor comprises a circuit for setting a desired motor speed and providing a speed-control signal, a circuit for sensing motor voltage and providing a motor voltage-related signal, a circuit for sensing current flow in the motor and providing a motor current-related signal, a summing point for combining the sensed current and sensed voltage-related signals to provide a motor speed-related signal, and a triggerable switch for combining the motor speed-related signal and the speed-control signal to provide an error signal for controlling the motor speed.

Abstract: 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.