Trimmers & Rheostats

Potentiometers are three-terminal variable resistors that allow adjustment of resistance by changing the position of a movable contact (wiper) along a resistive element. This adjustable contact provides a variable output voltage or resistance, enabling precise control over circuit levels.
Rheostats, on the other hand, are two-terminal variable resistors used to adjust current flow. In fact, a three-terminal potentiometer can function as a rheostat by leaving the third terminal unconnected, effectively operating as a two-terminal device.
Trimmers are a specialized type of potentiometer designed for infrequent adjustments, primarily used for device calibration. Typically, trimmers feature a small adjustment screw on the top, allowing fine-tuning of resistance at critical circuit points during manufacturing or recalibration. Mounted directly onto the circuit board, trimmers usually offer a narrow resistive range to achieve highly accurate settings. These components are common in machinery, heavy equipment, marine vehicles, audio devices, televisions, and other calibrated electronics.

Rheostat vs. Potentiometer
Though sometimes used interchangeably, potentiometers and rheostats serve distinct functions but share similar construction. Both are variable resistors with three terminals: two fixed terminals at each end of the resistive element and a third connected to a wiper (slider). The wiper moves across the resistive track, creating a variable resistance between the terminals.
Potentiometers typically adjust voltage by tapping the resistive element, while rheostats primarily vary current by altering resistance in series with a circuit. Some potentiometers are designed for linear resistance changes, while others—especially in audio applications—feature logarithmic (audio-taper) response curves to match human hearing sensitivity.