A potentiometer is a manually adjustable electrical resistor that uses three terminals. It is a simple electro-mechanical transducer. It converts rotary or linear motion from the operator into a change of resistance, and this change is used to control the levels of output. It is sometimes known as POTS.
For example, in a loudspeaker, a potentiometer is used to adjust the volume. In a television set, computer monitor or light dimmer, it can be used to control the brightness of the screen or light bulb.
WORKING OF A POTENTIOMETER
In a potentiometer an electrically conductive wiper slides across a fixed resistive element.
One terminal of the potentiometer is connected to a power source, and another is hooked up to a ground — a point with no voltage or resistance and which serves as a neutral reference point. The third terminal slides across a strip of resistive material. This resistive strip generally has a low resistance at one end, and its resistance gradually increases to a maximum resistance at the other end. The third terminal serves as the connection between the power source and ground, and it usually is operated by the user through the use of a knob or lever.
The user can adjust the position of the third terminal along the resistive strip to manually increase or decrease resistance. The amount of resistance determines how much current flows through a circuit.The output voltage is proportional to the distance travelled.
TYPES OF POTENTIOMETER
There are two types of potentiometer, linear and rotary potentiometer.
The linear potentiometer has a slide or wiper. The rotary potentiometer can be a single turn or multi turn.
A digital potentiometer adjusts and trims electronic circuits similar to variable resistors, rheostats and mechanical potentiometers. Sometimes called digital POT, RDAC, or digipot, these compact devices can be used to calibrate system tolerances or dynamically control system parameters.
The parameters while selecting a potentiometer:
•Shock and vibration
•Contamination and seals
•Easy to use
•High amplitude output
•Linear displacement measurement
•Rotary displacement measurement
•Liquid level measurements using floats
POTENTIOMETER Vs RHEOSTAT
Technically, a variable resistor is known as a rheostat, but potentiometers can be made to function as rheostats quite easily.
In its simplest configuration, a potentiometer may be used as a rheostat by simply using the wiper terminal and one of the other terminals, the third terminal left unconnected and unused. When only two of the three terminals are used, the potentiometer acts as a type of variable resistor. One end terminal is used, along with the sliding terminal.
Rheostats typically are used to handle higher levels of current or higher voltage than potentiometers. For example, rheostats might be used to control motors in industrial machinery.