Information about Potentiometer
A potentiometer is a variable resistor that can be used as a voltage divider.
Originally a potentiometer was an instrument to measure the potential (or voltage) in a circuit by tapping off a fraction of a known voltage from a resistive slide wire and comparing it with the unknown voltage by means of a galvanometer.
The present popular usage of the term potentiometer (or 'pot' for short) describes an electrical device which has a user-adjustable resistance. Usually, this is a three-terminal resistor with a sliding contact in the center (the wiper). If all three terminals are used, it can act as a variable voltage divider. If only two terminals are used (one side and the wiper), it acts as a variable resistor. Its shortcoming is that of corrosion or wearing of the sliding contact, especially if it is kept in one position.
The original potentiometer is a type of bridge circuit for measuring voltages by comparison between a small fraction of the voltage which could be precisely measured, then balancing the two circuits to get null current flow which could be precisely measured.
The word itself derives from the phrase "voltage potential," and "potential" was used to refer to "strength." The original potentiometers are divided into four main classes listed below.
In modern usage, a potentiometer is a potential divider, a three terminal resistor where the position of the sliding connection is user adjustable via a knob or slider. Potentiometers are sometimes provided with one or more switches mounted on the same shaft. For instance, when attached to a volume control, the knob can also function as an on/off switch at the lowest volume.
Ordinary potentiometers are rarely used to control anything of significant power (even lighting) directly due to resistive losses, but they are frequently used to adjust the level of analog signals (e.g. volume controls on audio equipment) and as control inputs for electronic circuits (e.g. a typical domestic light dimmer uses a potentiometer to set the point in the cycle at which the triac turns on). Potentiometers used to control high power are normally called rheostats.
A potentiometer is constructed using a flat graphite annulus (ring) as the resistive element, with a sliding contact (wiper) sliding around this annulus. The wiper is connected to an axle and, via another rotating contact, is brought out as the third terminal. On panel pots, the wiper is usually the centre terminal. For single turn pots, this wiper typically travels just under one revolution around the contact. 'Multiturn' potentiometers also exist, where the resistor element may be helical and the wiper may move 10, 20, or more complete revolutions.
In addition to graphite, other materials may be used for the resistive element. These may be resistance wire or carbon particles in plastic or a ceramic/metal mixture called cermet. One popular form of rotary potentiometer is called a string pot. It is a multi-turn potentiometer with an attached reel of wire turning against a spring. It's very convenient for measuring movement and therefore acts as a position transducer.
In a linear slider pot, a sliding control is provided instead of a dial control. The word linear also describes the geometry of the resistive element which is a rectangular strip, (not an annulus as in a rotary potentiometer). Because of their construction, this type of pot has a greater potential for getting contaminated.
Potentiometers can be obtained with either linear or logarithmic laws (or "tapers").
Most (cheaper) "log" pots are actually not logarithmic, but use two regions of different, but constant, resistivity to approximate a logarithmic law. A log pot can also be simulated with a linear pot and an external resistor. True log pots are significantly more expensive.
A rheostat is essentially a potentiometer, but is usually much larger, designed to handle much higher voltage and current. Typically these are constructed as a resistive wire wrapped to form a toroid coil with the wiper moving over the upper surface of the toroid, 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. They are usually used as variable resistors rather than variable potential dividers.
The same idea can be used to create Digital Volume Controls, attenuators, or other controls under digital control. Usually such devices feature quite a high degree of accuracy, and find applications in instrumention, mixing desks and other precision systems.
The DCP should not be confused with the digital to analogue converter (DAC) which actually creates an analogue signal from a digital one. A DCP only controls an existing analogue signal digitally. However, some DACs using resistive R-2R architecture have been functionally used as DCPs where the (varying) analogue signal is input to the reference voltage pin of the DAC and the digitally-controlled attenuated output is taken from the output of the DAC.
Feedback System DCPs
For the most part, the universe of feedback system design separates neatly into two fundamental design paradigms: analog-based designs and digital-based designs. Both design strategies are characterized by advantages and liabilities that generally make one or the other a clearly superior choice for any given application. Pure analog designs, for example, tend to display design simplicity and low development costs that play well in the context of smaller system applications. Digital-based designs, by contrast, have essentially unlimited flexibility in computation of the feedback function and therefore dominate in more complex feedback applications in which higher development costs (generally including software implementation) can be justified. Sometimes, a feature of particular utility in digital designs is the availability of digital memory with its ability to store feedback parameters for arbitrary lengths of time without drift. This makes possible a variety of system solutions including multiple system operating modes in which feedback values can be acquired in some modes and then applied in others.
But what about feedback systems that lie in between these clear opposites? What about, relatively simple cost-sensitive applications that would benefit from functions that are difficult to implement in analog circuits and would therefore require digital techniques?
One of the most common uses for modern low-power potentiometers is as audio control devices. Both sliding pots (also known as faders) and rotary potentiometers (commonly called knobs) are regularly used to adjust loudness, frequency attenuation and other characteristics of audio signals.
The 'log pot' is used as the volume control in audio amplifiers, where it is also called an "audio taper pot", because the amplitude response of the human ear is also logarithmic. It ensures that, on a volume control marked 0 to 10, for example, a setting of 5 sounds half as loud as a setting of 10. There is also an anti-log pot or reverse audio taper which is simply the reverse of a log pot. It is almost always used in a ganged configuration with a log pot, for instance, in an audio balance control.
A potentiometer used in combination with an inductor or capacitor acts as a "tone" control.
The 'modern' potentiometer can be used as a potential divider (or voltage divider) to obtain a manually adjustable output voltage at the slider (wiper) from a fixed input voltage applied across the two ends of the pot. This is the most common use of pots.
The voltage across
is determined by the formula:
The parallel lines indicate components in parallel. Expanded fully, the equation becomes:
Although it is not always the case, if is large compared to the other resistances (like the input to an operational amplifier), the output voltage can be approximated by the simpler equation:
As an example, assume
Since the load resistance is large compared to the other resistances, the output voltage
will be approximately:
Due to the load resistance, however, it will actually be slightly lower: ≈ 6.623 V.
One of the advantages of the potential divider compared to a variable resistor in series with the source is that, while variable resistors have a maximum resistance where some current will always flow, dividers are able to vary the output voltage from maximum (
) to ground (zero volts) as the wiper moves from one end of the pot to the other. There is, however, always a small amount of contact resistance.
In addition, the load resistance is often not known and therefore simply placing a variable resistor in series with the load could have a negligible effect or an excessive effect, depending on the load.
In mathematics, two quantities are called proportional if they vary in such a way that one of the quantities is a constant multiple of the other, or equivalently if they have a constant ratio.
..... Click the link for more information.
Originally a potentiometer was an instrument to measure the potential (or voltage) in a circuit by tapping off a fraction of a known voltage from a resistive slide wire and comparing it with the unknown voltage by means of a galvanometer.
The present popular usage of the term potentiometer (or 'pot' for short) describes an electrical device which has a user-adjustable resistance. Usually, this is a three-terminal resistor with a sliding contact in the center (the wiper). If all three terminals are used, it can act as a variable voltage divider. If only two terminals are used (one side and the wiper), it acts as a variable resistor. Its shortcoming is that of corrosion or wearing of the sliding contact, especially if it is kept in one position.
Potentiometer as measuring instrument
)
The original potentiometer is a type of bridge circuit for measuring voltages by comparison between a small fraction of the voltage which could be precisely measured, then balancing the two circuits to get null current flow which could be precisely measured.
The word itself derives from the phrase "voltage potential," and "potential" was used to refer to "strength." The original potentiometers are divided into four main classes listed below.
Constant current potentiometer
This is used for measuring voltages below 1.5 volts. In this circuit, the unknown voltage is connected across a section of resistance wire the ends of which are connected to a standard electrochemical cell that provides a constant current through the wire, The unknown emf, in series with a galvanometer, is then connected across a variable-length section of the resistance wire using a sliding contact(s). The sliding contact is moved until no current flows into or out of the standard cell, as indicated by a galvanometer in series with the unknown emf. The voltage across the selected section of wire is then equal to the unknown voltage. All that remains is to calculate the unknown voltage from the current and the fraction of the length of the resistance wire that was connected to the unknown emf. The galvanometer does not need to be calibrated, as its only function is to read zero. When the galvanometer reads zero, no current is drawn from the unknown electromotive force and so the reading is independent of the source's internal resistance.Constant resistance potentiometer
The constant resistance potentiometer is a variation of the basic idea in which a variable current is fed through a fixed resistor. These are used primarily for measurements in the millivolt and microvolt range.Microvolt potentiometer
This is a form of the constant resistance potentiometer described above but designed to minimize the effects of contact resistance and thermal emf. This equipment is satisfactorily used down to readings of 10 nV or so.Thermocouple potentiometer
Another development of the standard types was the 'thermocouple potentiometer' especially modified for performing temperature measurements with thermocouples. [1]Potentiometer as electronic component
)
Construction of a wire-wound circular potentiometer. The resistive element (1) of the shown device is trapezoidal, giving a non-linear relationship between resistance and turn angle. The wiper (3) rotates with the axis (4), providing the changeable resistance between the wiper contact (6) and the fixed contacts (5) and (9). The vertical position of the axis is fixed in the body (2) with the ring (7) (below) and the bolt (8) (above).
Ordinary potentiometers are rarely used to control anything of significant power (even lighting) directly due to resistive losses, but they are frequently used to adjust the level of analog signals (e.g. volume controls on audio equipment) and as control inputs for electronic circuits (e.g. a typical domestic light dimmer uses a potentiometer to set the point in the cycle at which the triac turns on). Potentiometers used to control high power are normally called rheostats.
Types of potentiometers
Low-power types
)
A typical single turn potentiometer
)
PCB mount trimmer potentiometers, or "trimpots", intended for infrequent adjustment.
Linear potentiometers
A linear pot 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 describes the electrical characteristic of the device, not the geometry of the resistive element.Logarithmic potentiometers
A log pot has 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 (or inverse logarithmic depending on type) function of the mechanical angle of the pot.Most (cheaper) "log" pots are actually not logarithmic, but use two regions of different, but constant, resistivity to approximate a logarithmic law. A log pot can also be simulated with a linear pot and an external resistor. True log pots are significantly more expensive.
High-power types
)
A high power toroidal wirewound rheostat.
Digital control
Digitally Controlled Potentiometers (DCPs) or digipots can be used in analogue signal processing circuits to replace potentiometers. They allow small adjustments to be made to the circuit by software, instead of a mechanical adjustment. Because this type of control is updated only infrequently, it often has a slow serial interface, like I²C. Some types have non-volatile memory to enable them to remember their last settings when the power is switched off.The same idea can be used to create Digital Volume Controls, attenuators, or other controls under digital control. Usually such devices feature quite a high degree of accuracy, and find applications in instrumention, mixing desks and other precision systems.
The DCP should not be confused with the digital to analogue converter (DAC) which actually creates an analogue signal from a digital one. A DCP only controls an existing analogue signal digitally. However, some DACs using resistive R-2R architecture have been functionally used as DCPs where the (varying) analogue signal is input to the reference voltage pin of the DAC and the digitally-controlled attenuated output is taken from the output of the DAC.
Feedback System DCPs
For the most part, the universe of feedback system design separates neatly into two fundamental design paradigms: analog-based designs and digital-based designs. Both design strategies are characterized by advantages and liabilities that generally make one or the other a clearly superior choice for any given application. Pure analog designs, for example, tend to display design simplicity and low development costs that play well in the context of smaller system applications. Digital-based designs, by contrast, have essentially unlimited flexibility in computation of the feedback function and therefore dominate in more complex feedback applications in which higher development costs (generally including software implementation) can be justified. Sometimes, a feature of particular utility in digital designs is the availability of digital memory with its ability to store feedback parameters for arbitrary lengths of time without drift. This makes possible a variety of system solutions including multiple system operating modes in which feedback values can be acquired in some modes and then applied in others.
But what about feedback systems that lie in between these clear opposites? What about, relatively simple cost-sensitive applications that would benefit from functions that are difficult to implement in analog circuits and would therefore require digital techniques?
Applications of potentiometers
Transducers
Potentiometers are also very widely used as a part of displacement transducers because of the simplicity of construction and because they can give a large output signal.Audio control
)
Sliding potentiometers ("faders")
One of the most common uses for modern low-power potentiometers is as audio control devices. Both sliding pots (also known as faders) and rotary potentiometers (commonly called knobs) are regularly used to adjust loudness, frequency attenuation and other characteristics of audio signals.
The 'log pot' is used as the volume control in audio amplifiers, where it is also called an "audio taper pot", because the amplitude response of the human ear is also logarithmic. It ensures that, on a volume control marked 0 to 10, for example, a setting of 5 sounds half as loud as a setting of 10. There is also an anti-log pot or reverse audio taper which is simply the reverse of a log pot. It is almost always used in a ganged configuration with a log pot, for instance, in an audio balance control.
A potentiometer used in combination with an inductor or capacitor acts as a "tone" control.
Theory of operation
)
A potentiometer with a resistive load, showing equivalent fixed resistors for clarity.
The 'modern' potentiometer can be used as a potential divider (or voltage divider) to obtain a manually adjustable output voltage at the slider (wiper) from a fixed input voltage applied across the two ends of the pot. This is the most common use of pots.
The voltage across
is determined by the formula:
The parallel lines indicate components in parallel. Expanded fully, the equation becomes:
Although it is not always the case, if
is large compared to the other resistances (like the input to an operational amplifier), the output voltage can be approximated by the simpler equation:
As an example, assume
, 
, 
, and 
.
Since the load resistance is large compared to the other resistances, the output voltage
will be approximately:
Due to the load resistance, however, it will actually be slightly lower: ≈ 6.623 V.
One of the advantages of the potential divider compared to a variable resistor in series with the source is that, while variable resistors have a maximum resistance where some current will always flow, dividers are able to vary the output voltage from maximum (
) to ground (zero volts) as the wiper moves from one end of the pot to the other. There is, however, always a small amount of contact resistance.
In addition, the load resistance is often not known and therefore simply placing a variable resistor in series with the load could have a negligible effect or an excessive effect, depending on the load.
Early patents
- Carbon track potentiometer/rheostat, Thomas Edison, 1872
- Mary Hallock-Greenewalt invented a type of nonlinear rheostat for use in her visual-music instrument the Sarabet (US Patent 1,357,773, 1920)
See also
- Potentiometric sensor
- Digipot
- Determining emf of primary cells using potentiometer
- Trimmer
- String Potentiometer
External links
- Information on a Variety of Commercial and Military grade Potentiometers: Which Is Right for My Application?
- Pictures of measuring potentiometers
- Electrical calibration equipment including various measurement potentiometers
- The Secret Life of Pots - Dissecting and repairing potentiometers
- Beginners' Guide to Potentiometers
- Making a rheostat
- Linear pot turned into log pot
- Potentiometer calculations as voltage divider - loaded and open circuit (unloaded)
- Application of Intersil Digitally Controlled Potentiometers (XDCP™) as Hybrid Analog/Digital Feedback System Control Elements
- DACs vs. Digital Potentiometers: Which Is Right for My Application?
In electronics, a voltage divider is a simple device designed to create a voltage (Vout) which is proportional to another voltage (Vin).
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potential may refer to the scalar potential or to the vector potential. In either case, it is a field defined in space, from which many important physical properties may be derived.
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galvanometer is a type of ammeter — an instrument for detecting and measuring electric current. It is an electromechanical transducer that produces a rotary deflection, through a limited arc, in response to electric current flowing through its coil.
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Electrical resistance is a measure of the degree to which an object opposes an electric current through it. The SI unit of electrical resistance is the ohm. Its reciprocal quantity is electrical conductance measured in siemens.
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In electronics, a voltage divider is a simple device designed to create a voltage (Vout) which is proportional to another voltage (Vin).
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A bridge circuit is a type of electrical circuit in which the current in a conductor splits into two parallel paths and then recombines into a single conductor, thereby enclosing a loop. It was originally used for measurement purposes, but can also be used in power supplies.
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electrochemical cell is a device used for creating an electromotive force (voltage) and current from chemical reactions. The current is caused by the reactions releasing and accepting electrons at the different ends of a conductor.
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Electric current is the flow (movement) of electric charge. The SI unit of electric current is the ampere (A), which is equal to a flow of one coulomb of charge per second.
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Definition
The amount of electric current (measured in amperes) through some surface, e.g...... Click the link for more information.
galvanometer is a type of ammeter — an instrument for detecting and measuring electric current. It is an electromechanical transducer that produces a rotary deflection, through a limited arc, in response to electric current flowing through its coil.
..... Click the link for more information.
..... Click the link for more information.
In electronics, a voltage divider is a simple device designed to create a voltage (Vout) which is proportional to another voltage (Vin).
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resistor is a two-terminal electrical or electronic component that resists an electric current by producing a voltage drop between its terminals in accordance with Ohm's law: The electrical resistance
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Loudness is the quality of a sound that is the primary psychological correlate of physical strength (amplitude).
Loudness, a subjective measure, is often confused with objective measures of sound pressure such as decibels or intensity.
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Loudness, a subjective measure, is often confused with objective measures of sound pressure such as decibels or intensity.
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A piece of audio equipment is any device designed principally to reproduce, record or process sound. This includes microphones, radio receivers, AV Receivers, CD players, tape recorders, amplifiers, mixing consoles, effects units and loudspeakers.
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A TRIAC, or TRIode for Alternating Current is an electronic component approximately equivalent to two silicon-controlled rectifiers (SCRs/thyristors) joined in inverse parallel (paralleled but with the polarity reversed) and with their gates connected together.
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Graphite (named by Abraham Gottlob Werner in 1789 from the Greek γραφειν (graphein): "to draw/write", for its use in pencils) is one of the allotropes of carbon.
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should be added to this article, to conform with Wikipedia's Manual of Style.
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A helix (pl: helices), from the Greek word έλικας/έλιξ
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A helix (pl: helices), from the Greek word έλικας/έλιξ
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4, 2
(mildly acidic oxide)
Electronegativity 2.55 (Pauling scale)
Ionization energies
(more) 1st: 1086.5 kJmol−1
2nd: 2352.6 kJmol−1
3rd: 4620.5 kJmol−1
Atomic radius 70 pm
Atomic radius (calc.
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(mildly acidic oxide)
Electronegativity 2.55 (Pauling scale)
Ionization energies
(more) 1st: 1086.5 kJmol−1
2nd: 2352.6 kJmol−1
3rd: 4620.5 kJmol−1
Atomic radius 70 pm
Atomic radius (calc.
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A cermet is a composite material composed of ceramic (cer) and metallic (met) materials. A cermet is ideally designed to have the optimal properties of both a ceramic, such as high temperature resistance and hardness, and those of a metal, such as the ability to undergo plastic
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Annulus (or anulus), being the Latin for "ring", is a term used to describe various ring-shaped objects:
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- Annulus (entomology), an antennal unit in simple antennae, or a ring-like marking or structure surrounding a joint or segment
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prevew not available
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logarithm (to base b) of a number x is the exponent y that satisfies x = by. It is written logb(x) or, if the base is implicit, as log(x).
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Taper may refer to:
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- Fishing rod tapers, a measure of the flexibility of a fishing rod
- In geometry, or in the casual description of a shaper or object, a gradual thinning or narrowing towards one end
- Machine taper, in machinery and engineering
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- proportionality, see Proportionality (disambiguation).
In mathematics, two quantities are called proportional if they vary in such a way that one of the quantities is a constant multiple of the other, or equivalently if they have a constant ratio.
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toroid is a doughnut-shaped object. The surface of such an object is known as a torus. Its annular shape is generated by revolving a circle around an axis external to the circle.
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A digipot is a digital potentiometer. This device is often used for trimming and scaling analog signals by micro-controllers. A digipot is an electronic IC that is often controlled by digital signals like I²C and SPI. It is used as volume control for amplifiers.
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Signal processing is the analysis, interpretation and manipulation of signals. Signals of interest include sound, images, biological signals such as ECG, radar signals, and many others.
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In telecommunications and computer science, serial communications is the process of sending data one bit at one time, sequentially, over a communications channel or computer bus. This is in contrast to parallel communications, where all the bits of each symbol are sent together.
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I²C is a multi-master serial computer bus invented by Philips that is used to attach low-speed peripherals to a motherboard, embedded system, or cellphone. The name stands for Inter-Integrated Circuit and is pronounced I-squared-C and also, incorrectly,
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attenuator is an electronic device that reduces the amplitude or power of a signal without appreciably distorting its waveform. Attenuators are usually passive devices made from resistors. The degree of attenuation may be fixed, continuously adjustable, or incrementally adjustable.
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In professional audio, a mixing console, digital mixing console, mixing desk (Brit.), or audio mixer, also called a sound board or soundboard, is an electronic device for combining (also called "mixing"), routing, and changing the level, tonality and/or
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