Tachometers measure rotational speed.
The tachometer is an instrument used for measuring rotational speed. The speed measured is usually that of a rotating shaft being driven by an engine. Tachometers are commonly installed in sports cars, large trucks, airplanes and ships to measure engine speed.
Electronic Tachometer
Electronic tachometers are designed to measure frequency, whether sine-wave or pulse. The input pulse waves, clipped and shaped by a discriminating circuit, are allowed to pass through a gating circuit to the displaying decade counters. The open time of the gate is controlled by a crystal oscillator or other suitable time base. The displaying counters are responsive to the number of pulses passed by the gate in a definite time.
Electric-Generator Tachometer
A widely used and flexible form of electric tachometer comprises a combination of electric generator and indicator. There are two principal forms: a DC generator with a DC voltmeter, and an AC generator with an AC voltmeter (or DC voltmeter with rectifier). In either case, the DC voltmeter is proportional to the shaft speed.
The AC generator form may include a circuit that is responsive to frequency and affected only slightly by voltage, giving greater accuracy.
Direct-Current Tachometer
The direct current tachometer is a small permanent-magnet generator with an output of 2 to 10 vaults per 1,000 revolutions/minute. A high-resistance voltmeter, calibrated in revolutions per minute, indicates the speed. The low starting and running torque makes it useful for measuring wind velocity. Besides measuring speed, the DC tachometer is used as a stabilizing component in velocity servomechanisms.
Alternating-Current Tachometer
The alternating current tachometer can be constructed with a stationary winding and a revolving permanent-magnet field. They generate voltage and frequency that are proportional to speed of rotation. The voltage may be rectified and applied to a permanent-magnet moving-coil instrument calibrated in revolutions per minute.
Eddy-Current Tachometer
The eddy current tachometer, also known as drag type, is widely used for automobile speedometers and for measuring aircraft engine speed. The magnetic fields caused by these eddy currents create a course that opposes the turning magnet field.
Tags: current tachometer, generator with, revolutions minute, calibrated revolutions, calibrated revolutions minute, engine speed, generator with voltmeter
