A potentiometer, commonly referred to as a pot, is an instrument used for measuring an electromotive force by balancing it against the potential difference produced by passing a known current through a known variable resistance. It’s a three-terminal resistor with a rotating or sliding contact that forms an adjustable voltage divider to measure electric potential (voltage). The instrument is passive, meaning it does not require a power supply or additional circuitry to perform its function.
If only two of the three terminals are used, the potentiometer acts as a variable resistor or rheostat. Resistors provide a fixed value of resistance to block the flow of electrical current around a circuit. It also produces a voltage drop in accordance with Ohm’s law.
The term is a combination of “potential difference” and “metering,” stemming from electrical development in the mid 1800s. The first slide-wire potentiometer was invented by Johann Christian Poggendorff in 1841.
Types of potentiometers
A variable potentiometer is an analogue device consisting of an electrical part that has a resistive element and a mechanical part that allows a wiper to move. There are four basic groups of variable potentiometers:
- A rotary pot varies its resistive value as a result of an angular movement. It is the most common type of potentiometer.
- A slide pot is designed to change the value of its contact resistance by means of a linear motion. Because of this, there is a linear relationship between the slider contact position and the output resistance.
- A preset or trimmer pot is a potentiometer designed to be installed and rarely adjusted thereafter. If it is adjusted, it will be to fine tune a circuit, such as a calibration.
- A rheostat is a two-connection variable resistor configured to provide resistive value within its ohmic range to control the flow of current running through them.
Uses for potentiometers
Potentiometers are commonly used for controlling electrical devices such as frequency attenuation and volume controls on audio equipment. It can be used to control a television’s brightness, contrast, and color response. If a potentiometer is operated by a mechanism, it can be used as a position transducer, such as a joystick.