Murphy OS77I-040NTO (20700124) Electronic Speed Switch

The OS77I-040NTO single set point speed switch is a compact all-electronic speed sensing module; 40-400 Hz range; normally open with distributor ignition input. It can be panel mounted via its trip set point potentiometer. 

This model is field adjustable and gives a transistor output when tripped. It is used to activate the engine shutdown circuit on engine overspeed.