User Manual

PCB mount trimmer potentiometers, or "trimpots", intended for infrequent adjustment
Electronic symbol for pre-set potentiometer
Others are enclosed within the equipment and are intended to be adjusted to calibrate equipment
during manufacture or repair, and not otherwise touched. They are usually physically much smaller
than user-accessible potentiometers, and may need to be operated by a screwdriver rather than
having a knob. They are usually called "preset potentiometers" or "trim[ming] pots". Some presets
are accessible by a small screwdriver poked through a hole in the case to allow servicing without
dismantling.
Multiturn potentiometers are also operated by rotating a shaft, but by several turns rather than less
than a full turn. Some multiturn potentiometers have a linear resistive element with a sliding contact
moved by a lead screw; others have a helical resistive element and a wiper that turns through 10,
20, or more complete revolutions, moving along the helix as it rotates. Multiturn potentiometers, both
user-accessible and preset, allow finer adjustments; rotation through the same angle changes the
setting by typically a tenth as much as for a simple rotary potentiometer.
A string potentiometer is a multi-turn potentiometer operated by an attached reel of wire turning
against a spring, enabling it to convert linear position to a variable resistance.
User-accessible rotary potentiometers can be fitted with a switch which operates usually at the anti-
clockwise extreme of rotation. Before digital electronics became the norm such a component was
used to allow radio and television receivers and other equipment to be switched on at minimum
volume with an audible click, then the volume increased, by turning a knob. Multiple resistance
elements can be ganged together with their sliding contacts on the same shaft, for example, in
stereo audio amplifiers for volume control. In other applications, such as domestic light dimmers, the
normal usage pattern is best satisfied if the potentiometer remains set at its current position, so the
switch is operated by a push action, alternately on and off, by axial presses of the knob.
Resistance–position relationship: "taper"