Tachometer/Tacho-Generator Simulation

DC Tacho-Generator

N
S
0 RPM

Output Voltage

0 V

DC Tacho-Generator Principles

DC Tacho-generators are small permanent magnet DC generators that work with the principle of electromagnetic induction between a permanent magnet and conducting coil.

The EMF induced in a DC generator is given by: E = kɸN

Where:

  • ɸ = flux (constant for permanent magnet)
  • N = rotational speed (RPM)
  • k = constant

Therefore, E = kg × N, where kg is the tacho-generator constant.

Thus, the output voltage is directly proportional to the rotational speed.

AC Tacho-Generator

Reference Coil
Quadrature Coil
0 RPM

Output Voltage

0 V

AC Tacho-Generator Principles

The principle of AC Tacho-Generator is similar to that of an induction generator.

Construction:

  • The rotor can be a thin light Aluminium disc or a squirrel cage rotor.
  • The stator coil has two windings: reference coil (direct axis coil) and quadrature coil, displaced by 90°.

Working:

  • The reference coil is excited by a sinusoidal voltage that produces an AC flux which is pulsating in nature.
  • The pulsating flux is composed of two oppositely rotating fluxes (forward and backward) of equal magnitude.
  • When the rotor is stationary, these two opposite fluxes produce equal and opposite voltages in the quadrature coil, resulting in zero output.
  • When the rotor rotates, the relative motion between the rotor and either of the forward or backward rotating magnetic fields changes, producing a non-zero voltage proportional to the speed.