Question

For a Tachometer measuring device, illustrate its elements and how each one of them is functioning, and give more information about its characteristics and applications

illustrate in 2 pages

Answer 1

Tachometer::

A digital tachometer is a digital device that measures and indicates the speed of a rotating object. A rotating object may be a bike tyre, a car tyre or a ceiling fan, or any other motor, and so on. A digital tachometer circuit comprises LCD or LED read out and a memory for storage. Digital tachometers are more common these days and they provide numerical readings instead of dials and needles.

Digital tachometer is an optical encoder that determines the angular velocity of a rotating shaft or motor. Digital tachometers are used in different applications such as automobiles, aeroplanes, and medical and instrumentation applications.

• What is a tachometer??

The word tachometer is derived from two Greek words: tachos means “speed” and metron means “to measure”. It works on the principle of a tachometer generator, which means when a motor is operated as a generator, it produces the voltage according to the velocity of the shaft. It is 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. Tachometers can be analog or digital indicating meters; however, this article focuses only on the digital tachometers.

• Working and Principle

The working principle of an electronic tachometer is quite simple. The ignition system triggers a voltage pulse at the output of the tachometer electromechanical part whenever the spark plug fires. The electromechanical part responds to the average voltage of the series of pulses and it shows that the average voltage of the pulse train is proportional to 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 an ambient temperature range of – 20 to +70°C (-4 to +158°F).

The tachometer in a vehicle enables the driver to select suitable throttle and gear settings for the driving conditions as prolonged use at high speeds can cause insufficient lubrication which will affect the engine. 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.

• Tachometers are classified into four types.

Based on the data acquisition technique, the tachometers are of the following types:

1. Contact type
2. Non Contact type

Based on the measurement technique, the tachometers are of the following types:

1. Time measurement
2. Frequency measurement

Type Explanation::

​*Contact Type Digital Tachometers

A tachometer which is in contact with the rotating shaft is known as contacttype tachometer. This kind of tachometer is generally fixed to the machine or electric motor. An optical encoder or magnetic sensor can also be attached to this so that it measures its RPM.

Digital Tachometers are capable of measuring low-speeds at 0.5 rpm and high speed at 10,000 rpm and are equipped with a storage pocket for the circumferential measurement. The specifications of this tachometer are LCD 5 digit display, operational temperature range of 0 to + 40oC, temperature storage range of – 20 to + 55o C and rotating speed of about 0.5 to 10,000 rpm.

*Non Contact type digital tachometers

A tachometer that does not need any physical contact with the rotating shaft is called as noncontact digital tachometer. In this type, a laser or an optical disk is attached to the rotating shaft, and it can be read by an IR beam or laser, which is directed by the tachometer.This type of tachometer can measure from 1 to 99,999 rpm; the measurement angle is less than 120 degrees, and the tachometer has a five-digit LCD display. These types of tachometers are efficient, durable, accurate, and compact, and also visible from long distance.

*Time measurement digital tachometers

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.

*Frequency measurement digital tachometers

A tachometer that calculates the speed by measuring the frequency of the pulses is called as frequency-based digital tachometer. This type of tachometer is designed by using a red LED, and the revolution of this tachometer depends on the rotating shaft, and it is more accurate for measuring high speed. These tachometers are of low-cost and high-efficiency, which is in between 1Hz-12 KHz.

*Applications

Automobiles,airplanes, trucks, tractors, trains and light rail vehicles, Laser instruments, Analog audio recording, Medical applications,