what is tachometer, and what are its applications

The tachometer is a measuring instrument that is used to measure the operating speed of an engine in revolutions per minute. It is also known as a revolution counter. The device can measure the rotational speed of the shaft or disc when the machine is in motion. It also indicates the angular speed of a rotating shaft. This instrument is usually used to estimate traffic speed and volume/flow. It is used in cars, aircraft or other vehicles. It shows the rate of rotation of engine crankshaft along with the marking that displays the safe range of rotational speed. An Electric Tachometer works on the principle of relative motion between the magnetic field and shaft of the coupled device. The motor of tachometer works as a generator, i.e. it produces the voltage based on the velocity of the shaft. It counts the number of rotations the crankshaft is making per minute. It is essential for the user to know the RPM of the engine and its operating range to avoid unnecessary damages. The device works on either an alternating or direct current.
Uses of tachometer:
It is used to measure rotational speed.
It can measure the flow of liquid with the help of an attached wheel with an inclined angle.
It is applicable for the medical sector to measure the blood flow rate of the patients.
It is used in vehicles to display the rate of engine crankshaft rotation.