Tachometer

Introduction A tachometer (revolution-counter, tach, rev-counter, RPM

gauge) is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine.

The device usually displays the revolutions per minute (RPM) on a calibrated analogue dial, but digital displays are increasingly common.

Types Of Tachometers Analog Tachometers

Digital Tachometers

Contact and Non-Contact Tachometers

Time and frequency measuring tachometers

Analog Tachometer

Digital Tachometer

Block Diagram

Working principle

• Pulses are fed to the tachometer at the frequency to be measured. A scale factor is applied to produce readings of desired types (linear speed, flow rates, etc)

• Two basic principles:-1. Principle of fixed time based tachometer2. Principle of reciprocal tachometer

Working Principle

The ignition system triggers a voltage pulse at the output of the tachometer electrochemichal part whenever the spark plug fires.

The electrochemical part responds to the average voltage of the series of pulses.

It shows that the average voltage of the pulse train is proportional to the engine speed.

The signal from the perception head is transmitted by standard twin screened cable to the indicator.

The tachometers are temperature compensated to be able to handle operations over a range of -20 to +70 degrees.

Applications Automobiles

Laser Instruments

Analog Audio Recording

Medical Applications

The tachometer in a vehicle enables the driver to select suitable throttle and gear settings for the driving conditions.

It enables the driver to prevent exceeding speed capability of sub-parts such as spring retracted valves of the engine, and overheating, thereby causing unnecessary wear or permanent damage and even failure of engines

Uses