potentiometer

A potentiometer is a three-terminal resistor with a movable contact, called a wiper, that slides along a resistive element. As the wiper moves, it changes the electrical resistance in the circuit, allowing an operator or control mechanism to adjust voltage, current, or signal level without switching. The three terminals are the two ends of the resistive track and the wiper contact itself.

The two main construction types are rotary and linear. Rotary potentiometers use a turn-shaft that rotates from roughly 0 to 270 degrees, making them compact and suitable for handheld adjustment or motor-driven control. Linear potentiometers use a sliding fader mechanism across a straight track, common in audio mixing consoles and test equipment. Both types contain a resistive element, usually a carbon or ceramic composition track, though precision applications use wire-wound resistors coiled around a ceramic former.

Voltage divider and rheostat operation

In voltage divider mode, all three terminals are used: the wiper output sits at a voltage proportional to its position between the two ends of the track, which carry a fixed voltage. This configuration appears in signal level controls, sensor interfaces, and feedback loops. In rheostat mode, only two terminals are used, typically the wiper and one end, so the potentiometer simply limits current in series with a load, like an old incandescent dimmer switch. The resistance element typically ranges from 100 ohms to 1 megohm, with linearity and lifespan varying with construction and price.

Mechanical wear and electrical noise are the primary failure modes. Rotary potentiometers can develop scratchy output after hundreds of thousands of cycles when the wiper contact no longer makes reliable contact with the resistive track, a condition called pot noise audible in audio systems. Sealed and conductive-plastic models last longer than open-carbon designs. Environmental exposure to dust, moisture, or salt spray accelerates corrosion of the contact and track.

The term potentiometer derives from its original laboratory use in measuring unknown voltages by balancing against a known voltage, though modern potentiometers are rarely used that way. Today the word describes any variable resistor with a sliding or rotating wiper, and it remains standard in control circuits, analog-to-digital converters, audio gear, and instrumentation where smooth manual or automated adjustment of voltage or current is needed.