Tachometer Generator

(or electric-generator tachometer), a microelectric machine that is used to convert the instantaneous values of the shaft or rotor speed of a machine or mechanism into an electrical signal. The operation of the tachometer generator is based on the fact that the angular rotational velocity of the generator rotor is proportional to the generated electromotive force if the excitation flux is constant.

A distinction is made between AC tachometer generators, which may be synchronous or asynchronous, and DC generators. DC tachometer generators are small commutator machines in which the excitation flux comes from a permanent magnet or a separate winding. Synchronous tachometer generators are small synchronous machines in which the rotor is a permanent magnet.

The most common type is the asynchronous generator, which is similar in design to an asynchronous electric motor with a hollow short-circuited rotor. In this design, two windings are located on the stator at an angle of 90°. One is the excitation winding, which is fed by alternating current of constant frequency and voltage; the other is the output winding, to which can be connected a measuring instrument, such as a voltmeter calibrated in revolutions per minute.

Tachometer generators are used as sensors of speed of rotation in various automatic devices and in electromechanical computer apparatus.