What is potentiometer and its types?

A resistor whose resistance value can be varied easily is called a potentiometer.The register used as volume control and tone control in a radio receiver is a potentiometer.

It consists of circular strip which is equal to 3/4th of ring. A carbon film is deposited on it. A moving arm which is connected to a shaft is mounted in such a manner that by rotating the shaft, any resistance value between 0 and maximum can be obtained. generally, the potential metre are made of carbon granules as stated above but wire wound potentiometers are also made for special purposes in the range of 1 to 100 ohms (example- for controlling the e.m.f. acting in a multimeter). carbon potentiometer are of following two types.

I) Linear potentiometer- in this type of potentiometer, the variation in resistance value is proportional to the angle rotated by the moving arm.

II). Logarithmic potentiometer- In a radio receiver or an audio amplifier the A.F. signal strength has to be increased ten, hundred or thousand times for increasing the output one, two or three times respectively. because of this reason only, the unit for the measurement of sound intensity has been selected and logarithmic unit called decibel.

Hence, potentiometer used in radio receiver or an audio amplifier are of logarithmic type. In this type of potentialmetre, the variation in resistance value is not proportional to the angle rotated by the movie arm. for equal angle rotation, the order of variation in the value of resistance is 1, 10, 100, 1000 omhs etc.

Pre-set:- it is a potential metre of very small size. it is generally mounted on the PCB of an equipment. its ohmic value can be adjusted by means of a small screw driver during alignment of the equipment. sometimes, a pre-set is referred as a 'POT' also. These are made in 'linear' as well as in 'logarithmic' types ranging from 100 to 1 mega ohm. These are extensively used in TV receiver etc.

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