A tachometer is an instrument that measures the rotation speed of a shaft or disk, such as in a motor or machine. It displays revolutions per minute (RPM) on an analog dial or digital display. There are analog and digital tachometers, as well as contact and non-contact types. Tachometers work by applying pulses from the rotating component to a scale that converts it to linear speed, RPM, or other desired units. They are used to monitor engine speed in automobiles and control speed in applications like medical devices and laser instruments.

1. Tachometer

2. 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.

3. Types Of Tachometers
 Analog Tachometers
 Digital Tachometers
 Contact and Non-Contact
Tachometers
 Time and frequency
measuring tachometers
Analog Tachometer
Digital Tachometer

4. Block Diagram

5. 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 tachometer
2. Principle of reciprocal tachometer

6. 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.

7. Applications
 Automobiles
 Laser Instruments
 Analog Audio Recording
 Medical Applications

8.  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