Autotech Corporation PS-127A Zero Speed Switch

The Autotech PS-127A Voltage Sensor (Zero Speed Switch) is a solid-state device that replaces motor-mounted mechanical speed switches by monitoring back-EMF from a coasting motor to detect zero speed. It is powered from 120 VAC, 50/60 Hz, and provides relay contacts rated for 10 A resistive at 115 VAC, with the sensing input able to accept 120/240/480 VAC for single- or three-phase systems. The PS-127A uses a locking-bushing potentiometer to set the switching point, includes a small differential of about 5% between turn-on and turn-off to prevent chatter, and a built-in LED indicates when the relay is energized; the sensing terminals tolerate up to 600 V overvoltage. Operating temperature range is -10°F to 135°F (-23°C to 57°C).