Potentiometer(variable resistor/rheostat). The potentiometer is a resistor where the resistance can be changed by the operator. The potentiometer is manufactured in different shapes and values.
Most potentiometers are set by turning a shaft, a screw or a slider. You can get potentiometers where the resistance changes in a linear fashion. Others may have a logarithmic resistance change. Though potentiometers may vary in shape, the basics are the same; A resistive track with connectors in each end, the third connector is a slide that can be moved to set the resistance.

The cheapest type to make is the carbon track potentiometer. The track is made of carbon on a substrate of phenol paper. This type has a poor linearity, a poor resolution and a short lifetime. It is not suited for high effects but are easy and cheap to manufacture.

A variation on the carbon track is the conductive polymer track. Here the track is made from fine-granulated carbon mixed with a polymer. The conductive polymer track has a long life and a high resolution but has a low effect tolerance. It also has a poor temperature stability.

Cerement track: this type has a good effect tolerance, high resolution, good temperature stability, and a long lifetime. The track is made from a mix of metal and ceramics, and printed on a ceramic surface.

Wire wound track. Here the track is made from a wire that is wound round a cor of ceramic or a fibre glass. This type of potentiometer is used for high effects, and has a good temperature stability. It has poor resolution, but by coating the track surface with a conductive polymer it can be increased.

The electronic symbol:
          ______
         |
      ___V__
  ---|______|---
         
        OR         
         ______
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        V
  ---/\/\/\/---

In electronics, a potentiometer or pot is a jargon term for any kind of variable resistor. Control of the pot may be exposed to the user via some kind of knob or slider, such as a volume control, or can be hidden as a preset control, adjustable with access to the circuit board using a screwdriver. Physically, a pot consists of a conducting shaft and armature. The end of the armature is a contact point, which moves along a track, usually made of carbon or some other conductive material. The shaft is one terminal, and the two ends of the track are the others.


----+
    |
    /
    /
--->/
    /
    /
    |
----+

The simplest pots are linear. The ratio of the resistances corresponds to the proportion of the distance along the track. Volume controls are different. As the human brain perceives volume on a log scale (decibels), volume controls are constructed to give a logarithmic relationship between the resistances, and the distance moved along the track.

Stereo hi-fi systems have double gang pots. A single shaft has two electrically isolated sections, moving pointers along separate, disconnected tracks. One track is used for the left channel and the other for the right channel.

In consumer electronics, pots have in the main, been replaced by digital circuitry, which has the advantage of having no moving parts to go wrong (apart from the up and down buttons of course).

A derogatory term among television engineers is "pot twiddler" - someone who can fix minor problems such as picture quality, by twiddling pots, but hasn't a clue how to diagnose, let alone fix anything more major.

Po*ten`ti*om"e*ter (?), n. [Potential + -meter.] Elec.

An instrument for measuring or comparing electrial potentials or electro-motive forces.

 

© Webster 1913.

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