The PS-119 Anti-Plugging Zero Speed Switch requires 115 VAC 50 or 60 HZ as a power source and works off the back EMF or generated voltage of a coasting motor as a sensing input.
As soon as the motor comes to a complete stop, the Zero Speed Switch senses the absence of back EMF and allows the motor to be started in either reverse or forward direction. Whenever the motor is rotating (regardless of applied power or momentum) the output of the MRS-1R module is de-energized and the motor ceases turning the output turns on.
The speed at which the output will turn on can be adjusted by a knob on this module. The MM11 memory module, allows you to restart instantly in the same direction of rotation if the motor is coasting, but prevents a restart in the opposite direction.