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A potentiometer is a three- terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. The measuring instrument called a potentiometer is essentially a voltage divider used for measuring electric potential voltage ; the component is an implementation of the same principle, hence its name.
Potentiometers are commonly used to control electrical devices such as volume controls on audio equipment. Potentiometers operated by a mechanism can be used as position transducers , for example, in a joystick. Potentiometers are rarely used to directly control significant power more than a watt , since the power dissipated in the potentiometer would be comparable to the power in the controlled load. There are a number of terms in the electronics industry used to describe certain types of potentiometers:.
Potentiometers consist of a 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. See drawing. Many inexpensive potentiometers are constructed with a resistive element B 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, for example, the effect of a multi-band equalizer hence the term "graphic equalizer".
The resistive element of inexpensive potentiometers is often made of graphite. 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.
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.
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. The relationship between slider position and resistance, known as the "taper" or "law", is controlled by the manufacturer. In principle any relationship is possible, but for most purposes linear or logarithmic aka "audio taper" potentiometers are sufficient.
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 USA 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. When a percentage is referenced with a non-linear taper, it relates to the resistance value at the midpoint of the shaft rotation.
The higher the percentage, the steeper the log curve. 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 proportional to the distance between them.
Linear taper potentiometers  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. 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. 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.
The most common way to vary the resistance in a circuit is to use a rheostat. The term "rheostat" is becoming obsolete,  with the general term "potentiometer" replacing it. For low-power applications less than about 1 watt a three-terminal potentiometer is often used, with one terminal unconnected or connected to the wiper. Where the rheostat must be rated for higher power more than about 1 watt , it may be built with a resistance wire wound around a semicircular insulator, with the wiper sliding from one turn of the wire to the next.
Sometimes a rheostat is made from resistance wire wound on a heat-resisting cylinder, with the slider made from a number of metal fingers that grip lightly onto a small portion of the turns of resistance wire. The "fingers" can be moved along the coil of resistance wire by a sliding knob thus changing the "tapping" point.
Wire-wound rheostats made with ratings up to several thousand watts are used in applications such as DC motor drives, electric welding controls, or in the controls for generators. The rating of the rheostat is given with the full resistance value and the allowable power dissipation is proportional to the fraction of the total device resistance in circuit. Charles Wheatstone 's rheostat with a metal and a wooden cylinder.
A digital potentiometer often called digipot is an electronic component that mimics the functions of analog potentiometers. Through digital input signals, the resistance between two terminals can be adjusted, just as in an analog potentiometer. There are two main functional types: volatile, which lose their set position if power is removed, and are usually designed to initialise at the minimum position, and non-volatile, which retain their set position using a storage mechanism similar to flash memory or EEPROM.
Usage of a digipot is far more complex than that of a simple mechanical potentiometer, and there are many limitations to observe; nevertheless they are widely used, often for factory adjustment and calibration of equipment, especially where the limitations of mechanical potentiometers are problematic.
A digipot is generally immune to the effects of moderate long-term mechanical vibration or environmental contamination, to the same extent as other semiconductor devices, and can be secured electronically against unauthorised tampering by protecting the access to its programming inputs by various means.
In equipment which has a microprocessor , FPGA or other functional logic which can store settings and reload them to the "potentiometer" every time the equipment is powered up, a multiplying DAC can be used in place of a digipot, and this can offer higher setting resolution, less drift with temperature, and more operational flexibility. A membrane potentiometer uses a conductive membrane that is deformed by a sliding element to contact a resistor voltage divider.
Linearity can range from 0. The repeat accuracy is typically between 0. The service life of these types of potentiometers is typically 1 million to 20 million cycles depending on the materials used during manufacturing and the actuation method; contact and contactless magnetic methods are available to sense position.
Membrane potentiometer manufacturers offer linear, rotary, and application-specific variations. Membrane potentiometers can be used for position sensing. For touch-screen devices using resistive technology, a two-dimensional membrane potentiometer provides x and y coordinates. The top layer is thin glass spaced close to a neighboring inner layer. The underside of the top layer has a transparent conductive coating; the surface of the layer beneath it has a transparent resistive coating.
A finger or stylus deforms the glass to contact the underlying layer. Edges of the resistive layer have conductive contacts. Locating the contact point is done by applying a voltage to opposite edges, leaving the other two edges temporarily unconnected.
The voltage of the top layer provides one coordinate. Disconnecting those two edges, and applying voltage to the other two, formerly unconnected, provides the other coordinate. Alternating rapidly between pairs of edges provides frequent position updates. An analog-to digital converter provides output data. Advantages of such sensors are that only five connections to the sensor are needed, and the associated electronics is comparatively simple. Another is that any material that depresses the top layer over a small area works well.
A disadvantage is that sufficient force must be applied to make contact. Another is that the sensor requires occasional calibration to match touch location to the underlying display. Capacitive sensors require no calibration or contact force, only proximity of a finger or other conductive object. However, they are significantly more complex. Potentiometers are rarely used to directly control significant amounts of power more than a watt or so.
Instead they are used to adjust the level of analog signals for example volume controls on audio equipment , and as control inputs for electronic circuits. For example, a light dimmer uses a potentiometer to control the switching of a TRIAC and so indirectly to control the brightness of lamps.
Preset potentiometers are widely used throughout electronics wherever adjustments must be made during manufacturing or servicing. User-actuated potentiometers are widely used as user controls, and may control a very wide variety of equipment functions. However they remain in many applications, such as volume controls and as position sensors. Low-power potentiometers, both slide and rotary, are used to control audio equipment, changing loudness, frequency attenuation, and other characteristics of audio signals.
It ensures that on a volume control marked 0 to 10, for example, a setting of 5 sounds subjectively half as loud as a setting of There is also an anti-log pot or reverse audio taper which is simply the reverse of a logarithmic potentiometer. It is almost always used in a ganged configuration with a logarithmic potentiometer, for instance, in an audio balance control.
Potentiometers used in combination with filter networks act as tone controls or equalizers.
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The third edition of the Dictionary of Ceramic Science and Engineering builds on the heavily revised 2nd edition which, in turn, expanded the original edition by some entries to include new fabrication, testing, materials, and vocabulary. The proven basis of the first two editions has been retained but new words and phrases have been added from the rapidly advancing electronic, nanoparticle and modern materials engineering fields. Additionally, all measurements in SI units are given to facilitate communication among the many sub-disciplines touched on by ceramics, ensuring that this publication remains the field's standard reference work for years to come. This extended edition of the Dictionary of Ceramic Science and Engineering ably follows its predecessors as an authoritative resource for students, researchers and professionals dealing with the processing of Materials.
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Add the following snippet to your HTML:. In this project, I am going to demonstrate how to use a potentiometer to dim LEDs. A potentiometer, or "pot" for short, is a variable resistor. It's the same type of control you'd use to change volume or dim a lamp.
A potentiometer is a three- terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. The measuring instrument called a potentiometer is essentially a voltage divider used for measuring electric potential voltage ; the component is an implementation of the same principle, hence its name. Potentiometers are commonly used to control electrical devices such as volume controls on audio equipment. Potentiometers operated by a mechanism can be used as position transducers , for example, in a joystick. Potentiometers are rarely used to directly control significant power more than a watt , since the power dissipated in the potentiometer would be comparable to the power in the controlled load. There are a number of terms in the electronics industry used to describe certain types of potentiometers:. Potentiometers consist of a 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. See drawing. Many inexpensive potentiometers are constructed with a resistive element B 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.
Account Options Sign in. My library Help Advanced Book Search. Get print book. Shop for Books on Google Play Browse the world's largest eBookstore and start reading today on the web, tablet, phone, or ereader. Annuaire statistique du commerce international , Volume 1. This two volume set is useful for analyzing trade by country and by commodity; performing trend analysis and projections; and understanding economic development planning and developing marketing strategies.
Account Options Sign in. My library Help Advanced Book Search. Get print book. United Nations Publications Amazon. Annuaire statistique du commerce international , Volume 2. United Nations. This fifty-sixth edition of the International Trade Statistics Yearbook provides the basic information for individual countries external trade performances in terms of value, as well as in volume and price, the importance of trading partners and the significance of individual commodities imported and exported. This edition shows annual statistics up to the year for countries or areas. It is published in two volumes. Volume I contains detailed data for individual countries or areas, and Volume II contains commodity tables showing the world trade of certain commodities analyzed by regions and countries.
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