Potentiometer | construction and working | Advantage | Types

Here we learn about Potentiometer | construction and working | Advantages and Disadvantages | Application and Types and Diagram.

Potentiometer :

1) It is also called variable resistance device, A  potentiometer for measurement of linear motion or angular niotion is shown in Figs, 2,1,4 (a) and (b) ' respectively, This device is in fact a variable resistor whose resistance varies on account of movement of the  slider or wiper over a resistance element,

2) The wiper is connected to an arm and. the arm moves in a linear direction when the linear motion under  measurement is applied to it,

3) The same is applicable for the angular measurement,  Here Fig, 2,1,4 (a) shows the linear measurement, On account of the movement of the arm, the wiper moves over the resistance element.
4) Thus the resistance of the potentiometer is changed and the change in resistance isi a function of movement (displacement) applied to it.
5) The change in the value of resistance may be measured by a wheatstone bridge. The change of resistance may  also be recorded by a bridge type recorder.


 Fig. Types of Potentiometer.

Fig. Construction and working of potentiometer.

The three major elements in potentiometric devices  are :
(a) Wirewinding
(b) Windingformer
(c)  Wiper

6) Materials used for wire winding are alloys of Cu-Ni, Ni-  Ch, etc. The wiper is spring elements made from  tempered, copper, bronze, phosphor  formers are ceramic; or of anodized aJlninWumindet.g  Sensitivity of a linear potentiometer is 
Sensitivity = Volts ÷ Full scale mechanical travel of wiper.

Potentiometer linearity :
1) A pot is said to be linear when the variation in resistance is directly proportional to the position of the contactor, i.e., the resjstance measured is a direct function of the position of the contactor over the resistance element.
2) However, in practice it is difficult to achieve a perfect linearity, hence, deviation limits are provided by calibration for better measurement results. Linearity should be greater than  0.5 % of full scale.

Advantages :  

1) They are inexpensive.
2) Operating principle is very simple.
3) They are useful for measurement of large amplitude of displacement, force, pressure, etc.

Disadvantages :  

1) Poor dynamic response because of friction.
2) Resolution is poor.
3) The problems with wiper contacts are that they wear out, become misalign and generate noise.

Applications :                                            

1) For precise measurement of displacement.
2) To control or change the brightness of lamp or LED.
3) For measurement of voltage in thermocouple.
4) Potentiometers can be used as motion sensor or position sensor.
5) They are used in many transducers to measure force, pressure, level etc.