Tachometer

The Tachometer is used to quantify the rotary speed of a rotating shaft. The instantaneous values of speed are indicated in terms of revolutions per minute and the usage of this instrument can be done in electrical and mechanical devices. The principle of working of the tachometer can be stated as; because there exists a relative movement in between the magnetic field and the shaft of a device following which a force of an electromotive is induced within the coil that is placed within the permanent magnet’s constant magnetic field of the permanent magnet. The electromotive force, which is developed, will be directly proportional to the speed of the shaft.

What is a Tachometer?

A tachometer is an instrument that can be either inbuilt in a specific device or it can be a separate freehand instrument. This instrument is used to quantify the rotational speed of a shaft or a disk of a motor or machine. Tachometers are also popularly known as ‘Revolution Counter’. Mechanical tachometers were used in earlier times but they are now replaced by electrical tachometers as they are more accurate and more precise. 

Types of Tachometers

Based on working principles and method of measurement, tachometers can be classified into the following types;

• Based on working principles:
  
  

  Electronic Tachometer- This type of tachometer is used in cars. One can find an electronic tachometer on the dashboard of any car. These devices are fitted to measure the driving speed of the vehicle in rotations per minute (RPM). The pulses of this tachometer are proportional to the speed of the car’s engine.
  
  Analog or Mechanical Tachometer- this tachometer can measure the speed of an engine with the help of a rotating mass that enables it to stretch and compress the mechanical spring in it. It counts the RPMs based on the period and using a series of reeds, it captures the necessary clues and gives us the proper reading (speed of the engine). The vibration frequency of the concerned machine can also be measured using a mechanical/analog tachometer. 

• Based on the measurement method:

Non-Contact tachometers- These are the modern-day tachometers that are very efficient, convenient, and compact. This type of tachometer does not require to be attached to the device or engine whose speed it needs to measure. This instrument measures the speed of the engine by using laser light and infrared light that reflect on a tape and mark a toral rotation. A beam of infrared light is sent on the shaft and receives the reflection which the instrument counts the entire rotational process and gives the RPM value on its display. Because they do not require to be attached to the shaft and can be used to measure the speed of multiple engines, it is widely used for their compactness and efficiency.

Contact Tachometers- These are the exact opposite of non-contact tachometers. They are fixed with the parent device which is the electric motor and figure out the RPM value by generating pulses from the shaft that drives the wheel. The tachometer displays the RPM value on its display. These tachometers use either an optical encoder or a magnetic sensor and are pretty much durable and accurate. 

Conclusion

Made to measure the operating speed of an engine, the tachometer is one of the most important instruments in industrial motor control. The safety of the engine and maintenance of a safe speed limit can be secured by using a tachometer. All motor vehicles must have a proper functioning tachometer with the appropriate tools that come with it. Tachometers are of different types and one must select the ideal tachometer as per their requirements. The instantaneous values of speed are indicated in terms of revolutions per minute and the usage of this instrument can be done in electrical and mechanical devices. Based on the simple working principle of the existence of a relative movement between the magnetic field and the shaft of a device post which electromotive force is induced in the coil placed inside the permanent magnet’s constant magnetic and the electromotive force, which is developed, will be inversely related to the speed of the shaft and that data will be processed by the machine and then displayed on the screen of the tachometer.