What is a potentiometer?

A potentiometer, commonly called a pot, is an adjustable electrical resistor that changes the level of output in electrical devices. Potentiometers are commonly used in audio systems, to adjust volume, or in some visual systems, to control brightness. Pots are also found in a wide variety of applications where precise resistance in a circuit is required.

For a quick explanation on how potentiometers work and what they are used for, tune in to GalcoTV:

 

 

Potentiometers are simple devices – only a few parts are needed in an effective pot. Their function relies primarily on a resistive element inside the device. Each end of the element is connected to a terminal integrated into a circuit. A third terminal connects to a wiper, a movable contact that rests on the resistor and serves as the variable component that adjusts the resistance of the circuit.

As the wiper moves along the resistor, the path of the current becomes shorter or longer, resulting in more or less resistance in the circuit – the further away the wiper contact is from the resistor’s end terminal, the greater the resistance in the circuit. The closer it is, the shorter the path, and thus, the less the resistance.

The third terminal is the defining feature of a potentiometer. One of the terminals on the resistor can be seen as an input terminal, and a second terminal connected to the wiper would be the output terminal. If only these two contacts were used, the device would instead be a rheostat. The third terminal, at the other end of the resistor, in conjunction with the circuit allows the wiper to determine the potential difference of the resistor. This gives a potentiometer its distinction as a voltage divider, with the wiper position determining the resistance ratio of the “first” resistor to the “second.”

 

potentiometer diagram

Diagram of a typical potentiometer.

 

Potentiometers are usually found in one of three configurations: rotary potentiometer, linear potentiometer, or trimmer potentiometer.

Rotary potentiometers, commonly called thumb- or thumbwheel pots, are the most common. The wiper moves along a circular path, usually adjusted by a knob or thumbwheel. They can come in several different variations, with single-turn being the most common. This pot only completes part of a full rotation, which provides enough control for most applications. Other variations are multi-turn pots, dual-gang, concentric, and servo.

Linear potentiometers, called slide or slider pots, use a lever or slider to move the wiper along a linear path. These types of potentiometers are used when a clear visual indication of the setting is needed. An array of slide pots is used as an equalizer, for example.

Trimmer potentiometers, or trimpots, are used for calibration and fine-tuning of circuit performance. They are typically used just once, sometimes sparingly, to achieve precise resistance in a circuit. A tool is needed to make adjustments to a trimpot (usually a small flat-head screwdriver).

All potentiometers function under certain conditions that describe the relationship between the position of the wiper and the resistance on the circuit. This relationship is the potentiometer’s taper. Two tapers are commonly used: linear taper and logarithmic taper.

If the potentiometer has a linear taper, the relationship between the position of the wiper and resistance is proportional. Position and resistance increase and decrease in a linear fashion, approximately with a one to one ratio. This type of taper is desired when the potentiometer needs to make precise adjustments.

For a potentiometer with a logarithmic taper, the relationship between the position of the wiper and resistance is represented by an exponential curve. Most pots with this taper don’t perform along a perfect exponential curve, instead they approximate logarithmic law. The resistive material is divided into two regions of differing resistance, creating a stepwise logarithmic taper. Potentiometers with tapers like these are commonly found in audio control systems (because they approximate human perception of volume).

For more information about potentiometers and other industrial electronic devices, contact Galco today!

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