Tachogenerator is an electromechanical device used for measuring shaft speeds and the speed of other rotational devices. The voltage this device outputs is proportional to its shaft speed. The tachogenerator finds its use in many different industries offering numerous advantages.
Most of the new tachogenerators are permanent-magnet types. Tachogenerators use a rotating armature, with one of the ends attached to a machine shaft to measure the rotational speed. The armature of these devices rotates in a fixed magnetic field, which means the rotation provides voltage proportional to the speed of the machine shaft speed.
With the machine shaft rotating, the armature of tachogenerators revolves within the magnetic field, which produces electromagnetic force proportional to the speed being measured. Since the permanent field is fixed, the electromagnetic force (voltage) is directly proportional to the speed. The voltage is then measured with a moving coil voltmeter with a uniform scale calibrated in speed directly. The series resistance exists only to limit the current under output short circuit condition. The rotation direction is indicated by the polarity of the output voltage. Using a commutator, tachogenerators collect and convert the electromagnetic force into DC electromagnetic force, while the current from commutator is collected with brushes.
In general, tachogenerators are used for measuring motor speed and the corresponding speed of powered equipment (mixers, conveyors, fans, machine tools, etc.). However, tachogenerators are also widely used as feedback components/sources in speed control circuits. These unique devices allow a continuous and proportional supply of voltage to the motor being tested, which results in higher speed ranges under various loads. Another common application of tachogenerators is the measurement and control systems to determine the directional indication.
By measuring the voltage with a tachogenerator, you will be able to easily determine the rotational speed of the mechanically attached device. The most common voltage signal range with tachogenerators is 0-10V. Tachogenerators are not able to produce voltage if there is no turning movement, so the 0 cannot be counted. When purchasing a tachogenerator, it is important to choose one with the right voltage-scale-speed. They come in different scales, so they can fit different applications.
Tachogenerators are commonly confused with tachometers, not only because of their similar names, but because they are both related to measuring rotational speed. However, these two devices should not be confused, because they are completely different in form and function.
