Murphy OS77D-900NTO (20700127) Electronic Speed Switch

The OS77D-900NTO single set point speed switch is a compact all-electronic speed sensing module; 1000-10,000 Hz range; normally open with magnetic sensor 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.