Device used to measure angular rotation speed. Tachogenerators can work as DC or AC generators.
DC generator:
The most commonly used process, in which a rotor turns in a magnetic field. The direct current generated in this way is proportional to the rotation speed over a wide range (Figure T 1).
Advantage: Can be used at low rotation speeds.
Disadvantage: The collector with brushes requires regular maintenance.
AC generator:
A rotor equipped with a permanent magnet turns within a stator with an electromagnet. In doing so, a sinusoidal output voltage is induced in the stator winding, whose amplitude is proportional to the rotation speed (Figure T 2).
Advantage: Low maintenance
Disadvantage: Measurement voltage must be rectified; not suitable for low rotation speeds.
Figure T 1: Principle of a direct current tachogenerator
Figure T 2: Principle of an alternating current tachogenerator