Tachogenerator

A tachogenerator, or tacho generator, is a device that converts rotational speed into an electrical signal. It is commonly used as a speed sensor and as a feedback element in motor control and automation systems. The output voltage or frequency is designed to be proportional to the shaft speed over a specified operating range.

Principle and construction: Tachogenerators rely on electromagnetic induction. DC tachogenerators typically use a rotor with permanent magnets or an excited field and a wound armature on the rotating shaft, producing a DC voltage proportional to speed. AC tachogenerators generate an alternating voltage whose frequency (and often amplitude) is proportional to speed; the signal is usually rectified or otherwise conditioned to produce a usable DC level for control or measurement.

Types and signals: DC tachogenerators provide a linear DC voltage proportional to speed, suitable for direct use in control loops. AC tachogenerators produce AC output that requires conditioning, such as rectification or frequency-to-voltage conversion, to be used as a speed signal.

Applications: They are used for speed measurement and feedback in servo and motor control systems, as well as in machine tools, textile machinery, printers, robotics, and automotive engine monitoring. They can also be employed to calibrate or test tachometers and other speed sensors.

Performance and considerations: Tachogenerators aim for a linear relation between speed and output within a defined range. Performance can drift with temperature, aging, and load. Wound versions may require maintenance for brushes and commutators. Tachogenerators are robust and simple, offering direct speed sensing, but higher-resolution or non-contact measurements may be obtained with encoders or Hall-effect sensors.