The word of tachometer is derived from two Greek word: tachos means "speed" and metron means "to measure". Its works on the principle of a tachometer generator, which means when a motor is operated as a generator, its produces the voltages according to the velocity of the shaft. Its also known as revolution-counter, and its operating principle can be electromagnetic, electronic or optical based. Power, accuracy, RPM range, measurements and display are the specifications of a tachometer.
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| Figure 1: digital tachometer |
Digital tachometer types
Digital tachometers are classified into four types based on data acquisition and measurement techniques. Based on the data acquisition technique, the tachometers are of the following types:
- Contact type
- Non contact type
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| Figure2 :contact type tachometer |
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| Figure 3 : non contact type tachometer |
Based on measurement technique, the tachometers are of the following types:
- Time measurement
- Frequency measurement
A tachometer that calculates the speed by measuring the time interval between incoming pulses is known as time based digital tachometer. The resolution of this tachometer is independent of the speed of the measurement and it is more accurate for measuring low speed.
A tachometer that calculates the speed by measuring the frequency of the pulses is called a frequency based digital tachometer. This type of tachometer is designed by using red LED, and the revolution of this tachometer depends on the rotating shaft, and its more accurate for measuring high speed.
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