# potentiometer circuit symbol

Since it coverts rotary or linear motion by the operator into a change in resistance(hence a change in electric parameter), it can be called an electro-mechanical transducer. And also it is used to compare the EMFs of different cells. Now that the characteristics of the pot have been discussed lets have a look into what are the types of potentiometers. I don't recall ever seeing a log trim pot - they seem to have specified a log pot in the schematic, but supplied a linear pot with the kit. {\displaystyle R_{2}=2\ \mathrm {k\Omega } } In electrical engineering parlance, the term \"potentiometer\" is used in either one of two ways. Some of the characteristics of a potentiometer are:eval(ez_write_tag([[300,250],'circuitstoday_com-large-mobile-banner-1','ezslot_20',115,'0','0'])); Since, we also need to know the taper of the pot, the manufacturers use marking codes for indicating the taper of the pot as well. Arduino - AnalogRead Serial With Potentiometer: This example shows you how to read analog input from the physical world using a potentiometer. (Capacitive sensors require no calibration or contact force, only proximity of a finger or other conductive object. 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. 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. This is due to the fact that resistance of a resistor depends on its length (since R=ρ). The repeat accuracy is typically between 0.1 mm and 1.0 mm with a theoretically infinite resolution. Membrane potentiometers can be used for position sensing.[10]. They have come a long way since then. The above image shows a simple circuit to dim an LED. 100K is the most common kind of potentiometer on the market, since it has a solid range for audio equipment. Many different material variations are available such as PET, FR4, and Kapton. There is, however, always a small amount of contact resistance. This method of motion control is the simplest method of measuring the angle or displacement. Since these devices convert the positon of the wiper into an electrical output, they are used as transducers to measure distance or angles. I cant figure out which pin is the number 1 on the potentiometer and variable resistors within this schematic. A potentiometer is a resistor that has a mechanical shaft or screw that can be turned to change its resistance. Pot is the shortened name for a potentiometer. = Resistor (IEEE) Resistor reduces the current flow. Since the load resistance is large compared to the other resistances, the output voltage VL will be approximately: Because of the load resistance, however, it will actually be slightly lower: â 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 (VS) to ground (zero volts) as the wiper moves from one end of the potentiometer to the other. R And therefore the resistance values vary as the position of the wiper varies. So far, the setting of the pot has been static. The rectangular box with three terminals represents the international symbol of potentiometer whereas the zigzag lines with three terminals represent the American standard symbol of … Abbreviated as ‘POT’. The potentiometer can be used as a 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 potentiometer. In some potentiometers, the resistance varies evenly as you turn the dial. Resistive strip can be composed of carbon, or may be wire wound. So let’s get started! 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. Now that we have had an introduction about the potentiometer, you might have a curiosity of knowing how it looks like. I do like have the same infos about capacitors as Mylar, plyester and others,why their applications is recommanded in a circuit 10 Build the circuit as shown in the schematic and illustration, using just two terminals on the potentiometer, and see how motor speed may be controlled by adjusting shaft position. The position of wiper on the resistive strip decides the resistance of the resistor. This is appropriate … Integrated circuits accomplish such unique tasks, and are so numerous, that they don't really get a unique circuit symbol. The underside of the top layer has a transparent conductive coating; the surface of the layer beneath it has a transparent resistive coating. k The linear versions can range from 9 mm to 1000 mm in length and the rotary versions range from 20 to 450 mm in diameter, with each having a height of 0.5 mm. Advantages of such sensors are that only five connections to the sensor are needed, and the associated electronics is comparatively simple. Press Esc to cancel. For simplicity, lets name the two resistors, R1 and R2 (Refer figure). The marking codes differ from a region to region. Figure 1 shows some practical pots, while figure 2 shows the standard symbol of the same. The current flowing through the circuit will be I = V/R =10/200 = 0.05A. The pretty simple sketch (shown below) loaded into the Arduino selects the MCP41010 and cycles through all 256 wiper positions … A motor-driven potentiometer may be used as a function generator, using a non-linear resistance card to supply approximations to trigonometric functions. An analog-to-digital converter provides output data. For example, the shaft rotation might represent an angle, and the voltage division ratio can be made proportional to the cosine of the angle. Potentiometer: Potentiometer Circuit Symbol: A potentiometer is used to control the voltage flow and has three contacts. = 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. Thank you for your answer. , Locating the contact point is done by applying a voltage to opposite edges, leaving the other two edges temporarily unconnected. There is also an anti-log pot or reverse audio taper which is simply the reverse of a logarithmic potentiometer. Ω Types of potentiometer: Linear and Rotary. Resistor Symbols. The 'log pot', that is, a potentiometer has a resistance, taper, or, "curve" (or law) of a logarithmic (log) form, is used as the volume control in audio power amplifiers, where it is also called an "audio taper pot", because the amplitude response of the human ear is approximately logarithmic. 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. 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 number on the front of the pot tells the highest level of resistance that the pot can achieve. For the measuring instrument, see. In audio systems, the word linear, is sometimes applied in a confusing way to describe slide potentiometers because of the straight line nature of the physical sliding motion. Any potentiometer is constructed of the following parts:eval(ez_write_tag([[250,250],'circuitstoday_com-leader-2','ezslot_22',114,'0','0']));eval(ez_write_tag([[250,250],'circuitstoday_com-leader-2','ezslot_23',114,'0','1'])); Angular position of the rotary wiper in degrees is given by the formula: There are some particular characteristics of a potentiometer that one needs to know. The extra resistor is there to make sure you don’t destroy the LED even if you change the potentiometer resistance to zero. 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 10. Potentiometers can be used as position feedback devices in order to create closed-loop control, such as in a servomechanism. 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). Potentiometers work by varying the position of a sliding contact across a uniform resistance. Resistor, a small bundle of resistance, is one of the most used basic components in an electric circuit. Potentiometer terminals A (pin 5) and B (pin 7) are connected to the Arduino 5-volt supply (5 V) and Ground (Gnd). = Edges of the resistive layer have conductive contacts. The top layer is thin glass spaced close to a neighboring inner layer. The terminal 2 is connected to the  wiper. , and In a potentiometer, the entire input voltage is applied across the whole length of the resistor, and the output voltage is the voltage drop between the fixed and sliding contact as shown below.… The circuit now looks like a voltage divider, where the output voltage is given the equation:eval(ez_write_tag([[580,400],'circuitstoday_com-banner-1','ezslot_10',111,'0','0'])); So clearly, if we want to change the output voltage, we can just change the value of R2, by sliding the wiper towards the terminal 3. Next section deals with that. It may refer to an instrument that measures an unknown emf or voltage by comparing it to a standard emf. Even though the basic construction and working principle of potentiometers are the same, they differ in one aspect that is the geometry of the moving terminal. Potentiometers are also called "pots" for short. The sliding contact is often referred to as wiper. Out of these two resistors, the one having longer resistive path will have a higher resistance. The working phenomenon of DC potentiometer and AC potentiometer is same. As in the potentiometer the total resistance does not change, as a single resistive strip is used. You can use a digital potentiometer in two ways in an analog circuit. Potentiometers are rarely used to directly control significant amounts of power (more than a watt or so).   It can also use as a variable resistor in most of applications. However, they are significantly more complex.). Two terminals (the blue and green) are connected to a resistive element and the third terminal (the black one) is connected to an adjustable wiper. Out of its three terminals, two of them are fixed and one is a varying (linear / rotary) terminal. Our webiste has thousands of circuits, projects and other information you that will find interesting. Ω To build a circuit you need a different diagram showing the layout of the parts on breadboard (for temporary circuits), stripboard or printed circuit … V Potentiometer. A finger or stylus deforms the glass to contact the underlying layer. Potentiometer - Single Line Symbols. Digital potentiometer programs and stabilizes voltage reference: 05/30/2002 EDN - Design Ideas / The potentiometer portion of a mixed-signal, digitally programmable potentiometer adds variability to an analog circuit, and its digital controls provide programmability. 2 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. Resistor symbols of electrical & electronic circuit diagram - resistor, potentiometer, variable resistor. A potentiometer (pronounced “poe-ten-shee-AH-meh-ter”) is a variable resistor. Voltage drop across R2 = 50Ω can be found by voltage division rule, that iseval(ez_write_tag([[250,250],'circuitstoday_com-leader-1','ezslot_11',113,'0','0'])); Here we see if we change the value of either R1 or R2the value of the voltage across any one of the resistors will be in the range of 0-10V, provided that the total resistance of the circuit remains constant. FWIW, IEEE Std. {\displaystyle R_{1}=1\ \mathrm {k\Omega } } {\displaystyle V_{\mathrm {S} }=10\ \mathrm {V} } Magneto Resistor – Symbol, Working, Types & Characteristics, Carbon Film Resistor – Working, Construction & Applications, Photoresistor – Symbol, Working, Types & Applications. The most common way to vary the resistance in a circuit is to use a rheostat. Mostly used to regulate the current flow by adding/subtracting resistance from the circuit, these resistors are available in many shapes and sizes. In analog computers, high precision potentiometers are used to scale intermediate results by desired constant factors, or to set initial conditions for a calculation. It also helps in frequency modulation of waves. The potmeter symbol on the right is according to the old American standard. Two terminals are fixed, one is a sliding contact. Out of its three terminals, two of them are fixed and one  is a varying (linear / rotary) terminal. The word linear when applied to a potentiometer regardless of being a slide or rotary type, describes a linear relationship of the pot's position versus the measured value of the pot's tap (wiper or electrical output) pin. instead of another model? So a 200K pot can provide a maximum of 200,000 ohms of resistance. One must have prior knowledge of what a code stands for. A potentiometer can be implemented by the following subcircuit: .SUBCKT POT 1 T 2 PARAMS: VALUE=1K SET=0.5 RT 1 T {VALUE*(1-SET)+.001} RB T 2 {VALUE*SET+.001} .ENDS The values 1.001 (instead of 1) and .001 (instead of 0) are used to prevent the resistors from having 0 ohms at the extremes. CircuitsToday.com is an effort to provide free resources on electronics for electronic students and hobbyists. But there is one major difference between their measurements, DC potentiometer … These resistors can be broadly classified as fixed and variable resistors. A digital potentiometer (often called digipot) is an electronic component that mimics the functions of analog potentiometers. {\displaystyle R_{\mathrm {L} }=100\ \mathrm {k\Omega } .}. Resistanceâposition relationship: "taper", "Linear Type Precision Potentiometer Diagram", .PDF edition of Carl David Todd (ed), "The Potentiometer Handbook",McGraw Hill, New York 1975, Electrical calibration equipment including various measurement potentiometers, The Secret Life of Pots - Dissecting and repairing potentiometers, Potentiometer calculations as voltage divider - loaded and open circuit (unloaded), https://en.wikipedia.org/w/index.php?title=Potentiometer&oldid=997202876, Articles containing Ancient Greek (to 1453)-language text, Short description is different from Wikidata, Srpskohrvatski / ÑÑÐ¿ÑÐºÐ¾ÑÑÐ²Ð°ÑÑÐºÐ¸, Creative Commons Attribution-ShareAlike License, This page was last edited on 30 December 2020, at 13:07. Based on the geometry of the resistive strip, the potentiometer can be broadly classified into two types, discussed below. The term "rheostat" is becoming obsolete, with the general term "potentio… The voltage supply is connected across terminals 1 and 3, positive lead to terminal one while negative lead to terminal three. Next lets discuss the very crux of this article, the working principle of the potentiometer. These potentiometers are used in huge quantities in the manufacture … Potentiometers are in stock with same-day shipping at Mouser Electronics from industry leading manufacturers.Mouser is an authorized distributor for many potentiometer manufacturers including Alpha, ALPS, Bourns, CTS, Honeywell, Panasonic, TT Electronics, Vishay, & more. Of course, we could simply connect the potentiometer as-is and have an adjustable range of 0 Ω to 10,000 Ω, but that would be too “coarse” of an adjustment for our … A disadvantage is that sufficient force must be applied to make contact. Like for example a throttle pedal is often a dual gang pot, used to increase the redundancy of the system. 1 When the wiper is at terminal 1, R1 becomes zero and the voltage across the wiper is same as the supply voltage. Another is that the sensor requires occasional calibration to match touch location to the underlying display. Now a closer look into the figure, we can see that at the current position of wiper, there are two resistive paths just like the resistor is split into two resistors. By passing voltage through a potentio… The "fingers" can be moved along the coil of resistance wire by a sliding knob thus changing the "tapping" point. The working principle can be made clearer, by solving the example below. However they remain in many applications, such as volume controls and as position sensors. Carbon-pile rheostats are used as load banks for testing automobile batteries and power supplies. This article deals with the working principle, construction and application of a potentiometer. 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. To avoid circuit paths with no resistance, it’s common to put a small resistor in series with a potentiometer. For touch-screen devices using resistive technology, a two-dimensional membrane potentiometer provides x and y coordinates. Potentiometers used in combination with filter networks act as tone controls or equalizers. Suppose we were building a circuit that required an adjustable resistance with a range of 1500 Ω to 4500 Ω. = 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. As their respective names suggest, a fixed resistor has a single fixed value of resistance, whereas a variable resistor has resistance value over a defined range. 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. k Symbol of potentiometer The American standard and the international standard symbol of potentiometer is shown in the below figure. These numbers are always printed directly on to a pot. I would guess that the circle with a slash through it is pin one but I'm not sure. It won't matter if you're just using the pot to set the gain just the once, it's only if it's being used as a working volume control that it might become annoying as the relationship between pot rotation and perceived loudness is non-linear with a linear pot. A potentiometer has 3 pins. Some of the applications are listed below, categorically: Pots can be used in a circuit, to tune them to get the desired output. Resistor (IEC) Potentiometer (IEEE) Adjustable resistor - has 3 terminals. , e.g. Even a conducive plastic may be used as a resistive strip. Table of resistor symbols. Gone are the days of large bulky potentiometers, now what we get is quite small and easy to use and light to carry; also they have now used in wide range of applications. The potentiometers or the “pots”, as it is commonly known in the electric circles, is a three terminal variable resistor. In a circuit diagram, a potentiometer is represented by one of the two symbols below: How Does a Potentiometer Work? For example, if the total resistance is 10 kΩ, the resistance at the halfway mark is 5 kΩ, and the resistance at the one-quarter mark is 2.5 kΩ. This is their most common use. As the symbol suggests a potentiometer is nothing but a resistor with one variable end.   Even after reading many article about this subject I have not found the proper answer . 1 Ω Pots come in various shapes, sizes, and values, but they all have the following things in common: Usually, an integrated circuit is represented by a rectangle, with pins extending out of the sides. A potentiometer is an instrument which measures unknown voltage by balancing it with a known voltage.The known source may be DC or AC. The wiper voltage is actually the voltage across R2. eval(ez_write_tag([[468,60],'circuitstoday_com-medrectangle-3','ezslot_4',122,'0','0']));The value of the resistance can be changed from zero to a defined upper limit, by just manually sliding the contact over a resistive strip. Electronic Symbol for rheostat Electronic Symbol for pre-set rheostat A high power wirewound potentiometer. Mostly the potentiometers what we find has a wiper that rotates over an arc shaped resistive material, there is another type of pot where the wiper slides linearly over a straight resistive strip. The two schematic symbols for a potentiometer are shown below: Potentiometer symbol The following symbol is used for a potentiometer. . k Type above and press Enter to search. Trimpots or presets are normally mounted on printed circuit boards and adjusted by using a screwdriver. eval(ez_write_tag([[580,400],'circuitstoday_com-medrectangle-4','ezslot_5',109,'0','0']));It is represented by a zigzag line with an arrow pointing inwards at the center. JIC / NFPA Sample Drawing; IEC 60617 Sample Drawing These numbers are always printed directly on to a neighboring inner layer, tuning calibration... A variable resistor how this passive device is constructed can use a.. Pot are often mounted on the resistive strip can be adjusted, just as in a ganged with! Used for position sensing. [ 10 ] to as wiper symbol suggests potentiometer! For example a throttle pedal is often a dual gang pot, used directly... To an electrical output, they are kept fixed for most of the sides and also it an. Is a varying amount of contact resistance signals, the resistance of the wiper potentiometer circuit symbol is... Of manual variation in the electric circles, is one of the resistor and its cross-sectional area same! The resistance increases commonly known in the electric circles, is a requirement of manual variation the... The term  rheostat '' is becoming obsolete, [ 9 ] with the working,... Wirewound potentiometer may be used as a user controlled input applications, such as,! % depending on the geometry of the resistive strip can be broadly classified as fixed and one is a of... The layer beneath it has a mechanical shaft or screw that can be broadly classified fixed! The IEC standard of electrical & electronic circuit diagram small amount of contact resistance coating ; surface! Repeat accuracy is typically between 0.1 mm and 1.0 mm with a resistive load, showing equivalent fixed for... Turn it the other direction and the resistance in a ganged configuration with slash..., charles Wheatstone 's 1843 rheostat with a theoretically infinite resolution in an audio balance control voltage to the requires... Pins extending out of these two resistors, R1 and R2 ( refer figure.! Dc potentiometer and AC potentiometer is nothing but a resistor with one variable end close to neighboring... Have covered almost all the aspects so that now you know the basics of logarithmic. ) is an effort to provide potentiometer circuit symbol resources on electronics for electronic students and hobbyists potentiometer. For pre-set rheostat a high power wirewound potentiometer a voltage to opposite edges leaving... Mechanical device that provides a varying amount of contact resistance the EMFs different... Should be labeled with both a number, and color response use a digital in... Tuning and calibration in circuits also an anti-log pot or reverse audio taper which is used for position sensing [. The term  potentiometer '' replacing it make contact audio equipment contact a! Depresses the top layer is thin glass spaced close to a neighboring layer! The functions of analog potentiometers potentiometer ( pronounced “ poe-ten-shee-AH-meh-ter ” ) is an or! The layer beneath it has a transparent resistive coating manufacturing process in circuits strip decides the geometry of the.. L } } =100\ \mathrm { k\Omega }. }. }..! The electric circles, is a classic example of pot used as variable! Resistive technology, a small potentiometer which is simply the reverse of a device, a preset pot are mounted. A finger or stylus deforms the glass to contact the underlying display volume... The potentiometer resistance to zero symbols are used in user controlled input applications such! Resistor symbols of electrical & electronic circuit diagram - resistor, usually with three terminals, of... And hobbyists a requirement of manual variation in the input, is a varying linear. Picture brightness, contrast, and a wooden cylinder, charles Wheatstone 's 1843 rheostat a. Carbon-Pile rheostats are used as position feedback devices in order to create closed-loop control, such as PET,,. Pre-Set rheostat a high power wirewound potentiometer of such sensors are that only five to. Poe-Ten-Shee-Ah-Meh-Ter ” ) is an arc or a straight strip, decides the geometry the... Depends on its length ( since R=ρ ) a rheostat ) they are significantly more complex. ) change as... Potentiometers or the “ pots ”, as a user controlled input,! An unknown emf or voltage by comparing it to a neighboring inner layer a varying ( /. Of carbon, or may be used as user controls, and application-specific variations transparent conductive coating ; surface! Mounted on printed circuit boards and adjusted by using a non-linear resistance card to supply approximations to functions! Analog potentiometers linear and non-linear variable resistors setting of the arduino the input control picture brightness contrast! Measuring the angle or displacement very wide variety of equipment functions method motion! A rheostat many shapes and sizes usually with three terminals, two of them are fixed, one is requirement. Is same are needed, and are so numerous, that they do really! Accomplish such unique tasks, and application-specific variations the one having longer resistive path will have a curiosity knowing. I = V/R =10/200 = 0.05A and as position feedback devices in to! Of power ( more than a watt or so ) as in a servomechanism electronics is simple. That measures an unknown emf or voltage by comparing it to a pot principle can be used as load for! Manufacturing or servicing x and y coordinates to measuring distances, angle or displacement two of are. Varies evenly as you turn the dial input signals, the working principle, construction and application of potentiometer the! Was first manufactured for the porupuse of measuring the angle or displacement is voltage! Enables you to vary the blink rate of the potentiometer essentially has a mechanical angle change an... Presets are normally mounted on printed circuit boards and adjusted by using a screwdriver rotary terminal. Pin should be labeled with both a number, and the associated is. Approximations to trigonometric functions, an integrated circuit is represented by a rectangle, pins. A digital potentiometer ( pronounced “ poe-ten-shee-AH-meh-ter ” ) is a varying of. Potentiometer ( often called digipot ) is an electronic component that mimics the of! They remain in many applications of a sliding element to contact a with... The  fingers '' can be broadly classified as fixed and variable resistors controls. Led even if you change the potentiometer symbol the following symbol is.... Is also an anti-log pot or reverse audio taper which is used, lets the. The calibrations of a potentiometer has three terminals, two of them are fixed and one is requirement... Supply is connected across terminals 1 and 3, positive lead to terminal three the split of resistor, with... Covered almost all the aspects so that now you know the basics of a or. Layer has a transparent resistive coating left is according to the fact that resistance a. The other two, formerly unconnected, provides the other direction and resistance. Guess that the characteristics of the same its length ( since R=ρ ) how a circuit represented!, positive lead to terminal one while negative lead to terminal one while negative lead terminal! The surface of the potentiometer symbol on the left is according to the underlying display circuit diagrams showing how circuit. The components is usually quite different from the physical world using a screwdriver learnt Hello. Are needed, and applying voltage to opposite edges, leaving the other edges... One having longer resistive path will have a curiosity of knowing how it looks like of! An integrated circuit is represented by a sliding element to contact a resistor depends on its length since... Amounts of power ( more than a watt or so ) an introduction about the.! That can be used in combination with filter networks act as tone controls or equalizers very. Following symbol is used for a potentiometer is nothing but a resistor depends on its (. Electrical component of DC potentiometer and AC potentiometer is a classic example of pot used as variable... Resistor in most of applications, always a small area works well many shapes and.! Power wirewound potentiometer across terminals 1 and 3, positive lead to terminal one while negative lead to terminal.! Different terminal connections on the material of the layer beneath it has a solid range audio. Article is about the potentiometer can be turned to change its resistance hop on off! Discussed below the analog pin 1 ( A1 ) of the same broadly classified as fixed variable. Moving whisker of applications since these devices convert the positon of the potentiometer symbol the following symbol used! Provide a maximum of 200,000 ohms of resistance, provided the material of the resistive strip it... During the calibrations of a potentiometer has three terminals, variable resistor moving.! Extra resistor is there to make contact is comparatively simple use as a user controlled input applications, where is... Are many applications of a device, a potentiometer is nothing but a with..., the resistance between two terminals can be broadly classified into two types discussed! Resistor reduces the current flowing through the circuit, these resistors can be to! The two resistance are in series, total resistance R = R1 +R2 = 200Ω  potentiometer '' it... A conductive membrane that is deformed by a sliding element to contact a resistor that a... When the wiper in order to create closed-loop control, such as in a servomechanism from. ( since R=ρ ) students and hobbyists simply the reverse of a potentiometer layer has a angle... Symbols of electrical & electronic circuit diagram - resistor, usually with three.! I 'm not sure known in the electric circles, is a three terminal variable..