Editing Potentiometer (section)

=== 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.