CAD CAM EDM DRO Home Page

There are a few different types of tachometers in general use in motion-control applications. Thee DC tachometer is almost certainly the oldest, as it is essentially identical to a permanent-magnet DC motor, with just a few optimizations to give better performance for the tachometer applications. Special care is made in designing the armature winding pattern to eliminate ripple in the DC output when the armature is turning at constant speed. The ideal DC tachometer generates a DC voltage that is directly proportional to shaft speed, and the polarity indicates shaft direction.

A second common type is the permanent-magnet AC tachometer, somewhat similar in construction to a stepper motor or brushless DC motor. Generally, the rotor contains a permanent magnet, and the stator contains fixed windings. Both the frequency and (AC) voltage produced are proportional to speed. An AC tachometer does not give direction information if it only has one output winding. It would be possible to determine direction with a 2nd winding in quadrature.

A third type is the AC induction tachometer, which requires AC excitation, and produces an output with the same frequency as the excitation source. But, the amplitude of the output is proportional to speed, and the phase of the output (with respect to the excitation) indicates direction.

To Home