Editing Potentiometer (section)

== Construction ==
[[File:Potentiometer cutaway drawing.png|thumb|upright=1.3|[[Cutaway drawing]] of potentiometer showing parts: (''A'') shaft, (''B'') stationary carbon composition resistance element, (''C'') phosphor bronze wiper, (''D'') shaft attached to wiper, (''E, G'') terminals connected to ends of resistance element, (''F'') terminal connected to wiper. A mechanical stop (''H'') prevents rotation past end points.]]
[[File:Single-turn potentiometer with internals exposed, oblique view.jpg|thumb|Single-turn potentiometer with metal casing removed to expose wiper contacts and resistive track]]

Potentiometers consist of a [[Electrical resistivity and conductivity|resistive element]], a sliding contact (wiper) that moves along the element, making good electrical contact with one part of it, electrical terminals at each end of the element, a mechanism that moves the wiper from one end to the other, and a housing containing the element and wiper.

Many inexpensive potentiometers are constructed with a resistive element (B in cutaway drawing) formed into an arc of a circle usually a little less than a full turn and a wiper (C) sliding on this element when rotated, making electrical contact. The resistive element can be flat or angled. Each end of the resistive element is connected to a terminal (E, G) on the case. The wiper is connected to a third terminal (F), usually between the other two. On panel potentiometers, the wiper is usually the center terminal of three. For single-turn potentiometers, this wiper typically travels just under one revolution around the contact. The only point of ingress for contamination is the narrow space between the shaft and the housing it rotates in.

Another type is the linear slider potentiometer, which has a wiper which slides along a linear element instead of rotating. Contamination can potentially enter anywhere along the slot the slider moves in, making effective sealing more difficult and compromising long-term reliability. An advantage of the slider potentiometer is that the slider position gives a visual indication of its setting. While the setting of a rotary potentiometer can be seen by the position of a marking on the knob, an array of sliders can give a visual impression of settings as in a [[graphic equalizer]] or [[Fader (audio engineering)|faders]] on a [[mixing console]].

The resistive element of inexpensive potentiometers is often made of [[graphite]]. Other materials used include resistance wire, carbon particles in plastic, and a ceramic/metal mixture called [[cermet]].

Conductive track potentiometers use conductive polymer resistor pastes that contain hard-wearing resins and polymers, solvents, and lubricant, in addition to the carbon that provides the conductive properties.

[[File:12 board mounted potentiometers.jpg|thumb|PCB mount [[trimmer (electronics)|trimmer]] potentiometers, or "trimpots", intended for infrequent adjustment]]

[[File:Pre-Set Potentiometer.png|thumb|upright=0.5|Electronic symbol for pre-set potentiometer]]

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 [[Helix|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, allowing 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 the same 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 [[dimmer]]s, 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.

Other potentiometers are enclosed within the equipment and are intended to only be adjusted when calibrating the 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 "trimmer", "trim[ming]", or "preset" potentiometers (or pots), or the genericized brand name "trimpot".

=== Resistance–position relationship: "taper" ===
[[File:Pots 10k 100k.jpg|thumbnail|upright|Size scaled 10k and 100k pots that combine traditional mountings and knob shafts with newer and smaller electrical assemblies. The "B" designates a linear (USA/Asian style) taper.]]

The relationship between slider position and resistance, known as the "taper" or "law", can be controlled during manufacture by changing the composition or thickness of the resistance coating along the resistance element. Although in principle any taper is possible, two types are widely manufactured: [[linear]] and [[logarithm]]ic (aka "audio taper") potentiometers.

A letter code may be used to identify which taper is used, but the letter code definitions are not standardized. Potentiometers made in Asia and the US are usually marked with an "A" for logarithmic taper or a "B" for linear taper; "C" for the rarely seen reverse logarithmic taper. Others, particularly those from Europe, may be marked with an "A" for linear taper, a "C" or "B" for logarithmic taper, or an "F" for reverse logarithmic taper.<ref>{{cite web|title=Resistor Guide|url=http://www.resistorguide.com/potentiometer/|access-date=3 January 2018}}</ref> The code used also varies between different manufacturers. When a percentage is referenced with a non-linear taper, it relates to the resistance value at the midpoint of the shaft rotation. A 10% log taper would therefore measure 10% of the total resistance at the midpoint of the rotation; i.e. 10% log taper on a 10&nbsp;kOhm potentiometer would yield 1&nbsp;kOhm at the midpoint. The higher the percentage, the steeper the log curve.<ref>{{cite web|last=Elliot|first=Rod|title=Beginners' Guide to Potentiometers|url=http://sound.whsites.net/pots.htm#markings|publisher=Elliott Sound Products|access-date=7 June 2012|url-status=dead|archive-date=23 April 2019|archive-url=https://web.archive.org/web/20190423021545/http://sound.whsites.net/pots.htm#markings}}</ref>

==== Linear taper potentiometer ====
A ''linear taper potentiometer'' (''linear'' describes the electrical characteristic of the device, not the geometry of the resistive element) has a resistive element of constant cross-section, resulting in a device where the resistance between the contact (wiper) and one end terminal is [[proportionality (mathematics)|proportional]] to the distance between them. Linear taper potentiometers<ref>{{cite web|last1=Peterson|first1=Phillip|title=Linear Type Precision Potentiometer Diagram|url=http://www.betatronix.com/uploads/2010%20SERIES.pdf|website=Precision Sensors|publisher=Betatronix|access-date=29 April 2015|archive-date=29 September 2015|archive-url=https://web.archive.org/web/20150929023752/http://www.betatronix.com/uploads/2010%20SERIES.pdf|url-status=dead}}</ref> are used when the division ratio of the potentiometer must be proportional to the angle of shaft rotation (or slider position), for example, controls used for adjusting the centering of the display on an analog cathode-ray [[oscilloscope]]. Precision potentiometers have an accurate relationship between resistance and slider position. [[File:Beckman Helipot potentiometer SA1400A 2007.075.002.jpg|thumb|[[Arnold Orville Beckman|Beckman]] Helipot precision potentiometer]]

==== Logarithmic potentiometer ====
A ''logarithmic taper potentiometer'' is a potentiometer that has a bias built into the resistive element. Basically this means the center position of the potentiometer is not one half of the total value of the potentiometer. The resistive element is designed to follow a logarithmic taper, aka a mathematical exponent or "squared" profile.
A logarithmic taper potentiometer is constructed with a resistive element that either "tapers" in from one end to the other, or is made from a material whose resistivity varies from one end to the other. This results in a device where output voltage is a logarithmic function of the slider position.

Most (cheaper) "log" potentiometers are not accurately logarithmic, but use two regions of different resistance (but constant resistivity) to approximate a logarithmic law. The two resistive tracks overlap at approximately 50% of the potentiometer rotation; this gives a stepwise logarithmic taper.<ref>{{cite web|title=Potentiometer taper|url=http://www.resistorguide.com/potentiometer-taper/|publisher=the Resistor Guide|access-date=19 November 2012}}</ref> A logarithmic potentiometer can also be simulated with a linear one and an external resistor. True logarithmic potentiometers are significantly more expensive.

Logarithmic taper potentiometers are often used for volume or signal level in audio systems, as human perception of audio volume is logarithmic, according to the [[Weber–Fechner law]].

==== Contactless potentiometer ====
Unlike mechanical potentiometers, ''non-contact potentiometers'' use an optical disk to trigger an infrared sensor, or a magnet to trigger a magnetic sensor (as long as there are other types of sensors, such as capacitive, other types of non-contact potentiometers can probably be built), and then an electronic circuit does the signal processing to provide an output signal that can be analogue or digital.

An example of a non-contact potentiometer can be found with the [https://www.edn.com/how-to-build-a-potentiometer-with-familiar-outputs-and-unfamiliar-qualities/ AS5600] integrated circuit.  However, absolute encoders must also use similar principles, although being for industrial use, certainly the cost must be unfeasible for use in domestic appliances.