Tachogenerators

Tachogenerators or tachometer generators are electromechanical devices that output a voltage proportional to their shaft speed. They are used to power tachometers and to measure the speed of motors, engines, and other rotational devices. Tachometers and tachogenerators should not be confused; even though they both relate to rotational speed measurement, they are very different in terms of form and functionality.

Tachogenerator Benefits

The main advantage of tachogenerators is that they are relatively resistant to corrosion and dust. Other benefits include:

They have linear characteristics.

Temperature compensation can be easily achieved.
They are capable of generating high voltages, despite being small in size.

Difference Between a Tachogenerator and Tachometer

Tachometers and Frequency Meters are used in automation and mechanical engineering applications to visualise, record, calculate and control frequencies and times. These devices process the signals of conventional incremental rotary encoders, sensors, light barriers, proximity switches or length measuring systems.

Tachogenerators generate and supply the outputs measured by the tachometers.

Tachogenerator Design

Modern tachogenerators tend to be permanent magnet types. These devices use a rotating armature, one end of which is attached to a machine shaft, to measure rotational speed. The armature rotates within a fixed magnetic field so that its rotation induces an electromotive force (voltage) proportional to the shaft's speed. The armature contacts are connected to a voltmeter circuit, which converts the voltage into a speed value.

Tachogenerator Types

DC Tachogenerator

A DC tachometer generator consist of main parts that include:

permanent magnet,
armature,
commutator,
brushes,
variable resistor,

moving coil voltmeter

The DC tachometer shaft is coupled with the machine which needs to be measured. It works on the principle that when the closed conductor moves in the magnetic field, EMF (electromagnetic field) induces in the conductor. The magnitude of the induced EMF depends on the flux link with the conductor and the speed of the shaft.

AC Tachogenerator

The AC tachogenerator is designed to reduce problems. Unlike the DC tachogenerator, the AC tachogenerator doesn’t have a commutator or brushes. The AC has been designed with a stationary armature and rotating magnetic field.

The rotating magnetic field induces the EMF in the stationary coil of the stator. The amplitude and frequency of the induced EMF are equivalent to the speed of the shaft. Thus, either amplitude or frequency is used for measuring the angular velocity.