Over-Speed Detector generates an over-speed signal when the speed of motor is greater than or equal to a predetermined speed. It consists of a source-sensor couple and a hand held device. Over speed detector monitors the frequency of the motor and inhibits the control signal using a relay if the speed surpasses a pre-set limit.
An electronic tachometers are used as a sensor that reads a magnetic strip and reports the rpm digitally. It is capable of producing mean readings rotational speed on components whose rpm is fluctuating. It is used as a velocity transducer for the track-accessing control system of a disk file is described. Rather than employing a conventional moving magnet and fixed-coil velocity transducer, this electronic tachometer combines information from the servo head position signal and from the actuator motor current to generate an accurate measurement of actuator velocity.