The potentiometer is a resistance with three leading out terminals and the resistance value can be adjusted according to a certain change ruleelement。Potentiometers usually consist of a resistor body and a movable brush.When the brush moves along the resistance body, an electric current that is related to the displacement is obtained at the output endresistanceorVoltage。
Potentiometer can be used as three terminalselementIt can also be used asTwo terminal elementuse.The latter can be regarded as oneVariable resistorBecause its role in the circuit is to obtain the output voltage which is related to the input voltage (external voltage), it is called a potentiometer.
Potentiometer (English: Potentiometer) isVariable resistorOne of.Usually byresistanceBody and rotation orSliding systemComposition, that is to move on the resistor body by a moving contact to obtain part ofVoltageOutput.
Function of potentiometer - adjustmentVoltage(includingDC voltageAndSignal voltage）And current.
The structural characteristics of the potentiometer - the resistor body of the potentiometer has two fixed ends. By manually adjusting the rotating shaft or sliding handle, changing the position of the moving contact on the resistor body changes the resistance value between the moving contact and any fixed end, thus changing the voltage and current.
The potentiometer is an adjustable electronicelement。It consists of a resistor and a rotating orSliding systemform.When a voltage is applied between two fixed contacts of the resistance body, the position of the contact on the resistance body can be changed by rotating or sliding the system, and a voltage that has a certain relationship with the position of the moving contact can be obtained between the moving contact and the fixed contact.It is mostly used asVoltage divider, then the potentiometer is a four terminalelement。The potentiometer is basicallySliding rheostat, there are several styles, generally used inloudspeaker boxVolume switch and laser headpowerSize adjustment, potentiometer is adjustableelectronic component。
For partial pressureVariable resistor。One or two movable metal contacts are pressed tightly on the exposed resistor body.The contact position determines the resistance between either end of the resistor and the contact.Wire wound, carbon film, solid core potentiometer according to material;According to the relationship between output and input voltage ratio and rotation angle, linear potentiometers (in linear relationship)functionPotentiometer (shown incurveRelationship).The main parameters areresistance、tolerance、Rated power。Widely used in electronic equipmentsoundAnd receiver for volume control.
distinguish
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potentiometer
Further analysis of the right waveform and expansion according to the time axis shows that although the left and right waveforms of the pulse potentiometer are the same.However, when turning left, in the first state, pin 1 first becomes low level than pin 2;In the second state, foot 2 also becomesLow level；In the third state, pin 1 becomes high level first than pin 2;In the fourth state, pin 2 also becomes high level;When the pulse potentiometer rotates to the right, the change rule of the output waveform of foot 1 and foot 2 is just opposite to that of the left.Therefore, according to the time recognition method (compare P1.0 with P1.1Low levelTime difference of occurrence and end) to identify whether the pulse potentiometer is left-handed or right-handed.In dynamic scanning, due tosampling frequency In fact, it is difficult to measure P1.0 and P1.1 waveforms due to the influence of operating speed and other factors;It is also difficult to accurately measure the time difference between the occurrence and end of P1.0 and P1.1 low levels, and only can quickly sample P1.0 and P1.1 levels.The waveform shown in Figure 1 is expanded according to the time axis. Each time the combined levels of P1.0 and P1.1 are 01 00 10 11 in turn, four status codes form a byte, namely, 4BH, which means that the volume of the left rotation one bit decreases by 1.And every time P1.0 and P1.1 combination levels are 10 00 01 11Status codeWhen forming a byte, i.e. 87H;It means that the volume of the right rotation bit 1 is increased by 1.Here, "4BH" is called a left-handed one bit signature, and "87H" is called a right-handed one bit signatureSignature code。The task of programming is to rotate the pulse potentiometerprocessThe two characteristic codes are identified in the, and based on this, the volume is increased or decreased.In actual programming, these two characteristic codes can be identified by different methods.However, after comparison in practice, it is an ideal method to realize programming with state (position) sampling method.This method has no special requirements for sampling frequency and operating speed, and can also be omittedtimerAnd interrupt resources can be completed only in the main program, and it has the advantages of simple programming, strong anti-interference ability and reliable work.
There are three situations of pulse potentiometer during operation: one is that it is not rotated and stays at a certain positionstate(location);Second, although it was rotated, it did not complete onecycle(4 states) and stay in a certain state;The third is to be rotated continuously for more than one cycle.The state (position) sampling method is to accurately track, identify and record each state value (including the position value and its correspondingSignature code）。At the beginning of the program, it is necessary to identify the current position of the pulse potentiometer and its corresponding characteristic code;Then keep tracking the scanning recordspulseEach change process of potentiometer.Obviously, only when the pulse potentiometer is rotated to the fourth state can a required signature appear. The program will increase or decrease the volume according to the nature of this signature.
Compliance
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Conformity is also called conformity, which refers to the conformity between the actual output function characteristics of the potentiometer and the required theoretical function characteristicsdegree。It is expressed as the percentage of the total external voltage with the maximum deviation between the actual and theoretical characteristics, which can represent theaccuracy。
Resolution
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The resolution depends on the theoretical accuracy of the potentiometer.aboutWire wound potentiometerFor linear potentiometers, the resolution is expressed as the percentage of the resistance change caused by each turn of moving contact on the winding and the total resistance.For potentiometers with functional characteristics, resolution is a variable because the resistance of each turn on the winding is different.At this time, the resolution of potentiometer generally refers to the function characteristiccurveThe average resolution of the section with the maximum upper slope.
Sliding noise
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Sliding noiseIt is the unique noise of potentiometer.When changing the resistance value, due to improper distribution of potentiometer resistance, improper coordination of rotation system and existence of potentiometercontact resistanceWhen the moving contact moves on the surface of the resistance bodyuseful signal In addition, there is also noise that fluctuates with the signal.
For wire wound potentiometers, in addition to the above contact noise between moving contacts and windings, there are also resolution noise and short circuit noise.The resolution noise is caused by the stepwise change of resistance, while the short-circuit noise is generated when the moving contact moves on the winding and shortens the adjacent wire turns. It is proportional to the current flowing through the winding, the resistance of the wire turns, and the contact resistance between the moving contact and the winding.
Mechanical life
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The mechanical life of potentiometer is also calledabrasionService life, usually expressed by mechanical durability.Mechanical durability refers to the total number of reliable movements of the moving contact of the potentiometer under the specified test conditions, usually expressed in "weeks".The mechanical life is related to the type, structure, material and manufacturing process of the potentiometer, and the difference is quite large.
In addition to the above characteristic parameters, the potentiometer also hasRated power. Allowable deviation of resistance value, maximumworking voltage Rated working voltage, insulation voltage, temperature parametersNoise electromotive forceAnd high-frequency characteristicsresistorThe corresponding characteristic parameters have the same meaning.
classification
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Related books
The key components of the potentiometer areResistorandbrush。Potentiometers can be divided into several types according to the structure between them and whether there is a switch.Potentiometers can also be classified according to the material of resistance body, such as wire winding, synthetic carbon filmMetallic glassFor glaze, organic solid core and conductive plastic, the electrical properties mainly depend on the materials used.Also usefulMetal foil、Metallic filmPotentiometer made of the resistor body with the metal oxide film has a special purpose.Potentiometers are distinguished according to the use characteristics, including universal and highaccuracy, HighResolutionPotentiometers with high resistance, high temperature, high frequency and high power;According to the resistance adjustment mode, there are adjustable type, semi adjustable type and fine adjustment type, the latter two are also called semi fixed potentiometers.In order to overcome the adverse impact of the moving contact of the brush on the resistor on the performance and life of the potentiometer, there are contactless contactless potentiometers, such as photosensitive andMagnetic potentiometerFor a small number of special applications.
Adjustable winding potentiometer
Wirewound potentiometer:It has the advantages of high precision, good stability, small temperature coefficient, reliable contact, high temperature resistance, and strong power load capacity.shortcomingThe resistance range is not wide enough, the high-frequency performance is poor, the resolution is not high, and the wire wound potentiometer with high resistance is easy to break, the volume is large, and the price is high.This potentiometer is widely used inElectronic instrument, instrument.The resistance body of wire wound potentiometer is composed ofResistance wireIt is formed by winding on the insulation. There are many types of resistance wires. The material of resistance wires is selected according to the structure of the potentiometer, the space to hold the resistance wires, the resistance value and the temperature coefficient.The thinner the resistance wire, the greater the resistance value and resolution in a given space.However, the resistance wire is too thin and easy to be disconnected during use, which affects the life of the sensor.
Carbon film potentiometer
synthesisCarbon film potentiometer：haveresistanceIt is characterized by wide range, good resolution, simple process and low price, but it has large dynamic noise and poor moisture resistance.This type of potentiometer should befunctionType potentiometer, atconsumer electronicsA large number of applications.The production of carbon film can be automated by using printing technology.
Organic solid core potentiometer:Wide resistance range, high resolution, good heat resistanceOverload capacityStrong, good wear resistance, high reliability, but poor resistance to damp heat and dynamic noise.This kind of potentiometer is generally made into small semi fixed form, which is used for micro calling in the circuit.
Metal glass glaze potentiometerIt not only has the advantages of organic solid core potentiometer, but also has smallerResistance temperature coefficient(Similar to wire wound potentiometer), but with large dynamic contact resistance and large equivalent noise resistance, it is mostly used for semi fixed resistance adjustment.This type of potentiometer has developed rapidly, and its ability to withstand temperature, humidity and load impact has been improved, and it can work reliably under harsh environmental conditions.
Conductive plastic potentiometer：Wide resistance range, high linear accuracy, strong resolution, and wear resistancelifeExtremely long.Although its temperature coefficient and contact resistance are large, it can still be used in analog and servo systems of automatic control instruments.
Digital potentiometer：Potentiometer made with integrated circuit technology;Integrate a series of resistors into a chip, and use MOS tubes to control the series of resistors
Network and public terminal connection;The control precision is determined by the bit number of control, generally 8 bits, 10 bits, 12 bits, etc;It can be used in analog circuit for impedance matching, amplification control of amplification loop, etc;The trouble of jitter adjustment operation is avoided;It provides a convenient way for automatic gain, voltage change and impedance matching of equipment.
Multi turn precision adjustable potentiometer
Multi turn precisionadjustable trim pot ：In some industrial control and instrument circuits, high adjustable precision is usually required.In order to meet production needs.This type of circuit uses a multi turn adjustable potentiometer.This type of potentiometer has a large step range!High precision.
Classification of resistance materials
Carbon Film: use carbon film asresistanceMembrane.
Metal Film: special cermet film made of ceramic and metal materials is used as resistance film.
Wirewound: useWireWinding is used as resistance.Compared with carbon film or porcelain metal film, it can withstand higher power.
Structural classification
Rotary: common form.The general rotation angle is about 270~300 degrees.
Single loop: common form.
Multi turn type: used for occasions requiring precise adjustment.
Linear sliding type: usually used forMixerIt is convenient to immediately see the volume position and perform fade in and fade out control.
Quantity classification
Single connection type: one rotating shaft only controls a single potentiometer.
Dual: two potentiometers use the same rotary axis for control, mainly used in dual channels, and can control two channels at the same time.
Classification of resistance change scale
Linear scaling:Resistance valueThe change of is linear with the rotation angle or moving distance. This potentiometer is called B-type potentiometer.
Logarithmic scale: the change of resistance value is logarithmic to the rotation angle or moving distance. This potentiometer is mainly used for volume control, of which the commonly used type A potentiometer is suitable for occasions where the volume is high in the clockwise direction and low in the counterclockwise direction;In addition, there is another C-type potentiometer with logarithmic scale and opposite direction of change.
Classification according to material of resistor
Potentiometers can be divided into wire wound potentiometers and non wire wound potentiometers according to the material of resistance body.Wire wound potentiometers can be divided into general wire wound potentiometers, precision wire wound potentiometers, high-power wire wound potentiometers and preset wire wound potentiometers.Non wirewound potentiometers can be divided intoSolid potentiometerAnd membrane potentiometer.Among them, solid potentiometer is divided into organic synthetic solid potentiometer, inorganic synthetic solid potentiometer and conductive plastic potentiometer.Membrane potentiometer can be divided into carbon film potentiometer and metal film potentiometer[1]。
Classification according to regulation mode
Potentiometers can be divided intoRotary potentiometer, push-pull potentiometer, straight slide potentiometer, etc[1]。
Classification according to the change rule of resistance value
Potentiometers can be divided into linear potentiometers, exponential potentiometers and logarithmic potentiometers according to the change law of resistance value[1]。
Classification according to structural characteristics
According to its structural characteristics, potentiometers can be divided into single turn potentiometers, multi turn potentiometers, single link potentiometersDouble potentiometerMultiple potentiometers, tap potentiometers, potentiometers with switches, locking potentiometers, non locking potentiometers and patch potentiometers[1]。
Classification by driving mode
The potentiometer can be divided into manual adjustment potentiometer and electric adjustment potentiometer according to the driving mode[1]。
Other special types
Potentiometer with switch: usually used to combine the volume switch with the power switch, that is, rotate it counterclockwise to the bottom to cut off the switch and close itPower Supply。[2]
effect
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The main functions of potentiometer in the circuit are as follows
The potentiometer is continuously adjustableresistorWhen adjusting the rotary handle or sliding handle of the potentiometer, the moving contact slides on the resistance body.At this time, the output voltage related to the applied voltage of the potentiometer and the angle or travel of the movable arm can be obtained at the output terminal of the potentiometer.
2. Used as rheostat
When the potentiometer is used as a rheostat, it should be connected into devices at both ends, so that a smooth and continuous resistance value can be obtained within the travel range of the potentiometer.
3. Used as current controller
When the potentiometer is used as a current controller, one of the selected current output terminals must be a sliding contact terminal.
matters needing attention
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1. The resistance body of the potentiometer is mostly made of polycarbonate synthetic resin, and should avoid contact with the following items: ammonia, other amines, alkaline water solutions, aromatic hydrocarbons, ketones, lipid hydrocarbons, strong chemicals (high pH value), or its performance will be affected.
2. When welding the terminals of the potentiometer, the use of water capacitive flux should be avoided, otherwise it will encourage metal oxidation and material mildew;Avoid using inferior flux. Poor soldering may cause difficulty in tin loading, resulting in poor contact or open circuit.
3. If the welding temperature of the potentiometer terminal is too high or the welding time is too long, the potentiometer may be damaged.Pin terminal welding should be completed within 3 seconds at 235 ℃± 5 ℃. The welding should be more than 1.5 mm away from the potentiometer body. Do not use soldering tin to flow through during weldingCircuit board；The welding of wire terminal shall be completed within 3 seconds at 350 ℃± 10 ℃.And the terminal should avoid heavy pressure, otherwise it is easy to cause poor contact.
4. When welding,rosinThe height of (flux) entering the printing machine board shall be adjusted properly, and the flux shall be prevented from invading the inside of the potentiometer, otherwise the brush andresistancePoor body contact leads to poor INT and noise.
5. Potentiometers are best used forVoltageAdjust the structure and select the "1" pin for grounding;The current regulating structure should be avoided, because the contact resistance between the resistance and the contact piece is not conducive to the passage of large current.
6. The surface of potentiometer shall be free from condensation or water drops, and shall not be used in wet places to prevent insulation deterioration or short circuit.
7. When installing the "rotary" potentiometer to fix the nut, the strength should not be too tight to avoid damaging the thread or poor rotation;When installing the "iron case direct sliding" potentiometer, avoid using too long screws, otherwise it may hinder the movement of the sliding handle, or even directly damage the potentiometer itself.
8. Put the knob on the potentiometerprocessThe thrust used shall not be too large (not exceeding the parameter index of the axle thrust and tension in the Specification), otherwise the potentiometer may be damaged.
9. The rotary operating force (rotation or sliding) of the potentiometer will become lighter with the increase of temperature, and become tighter with the decrease of temperature.If the potentiometer is inLow temperature environmentIn order to use special low temperature resistant grease, it is necessary to specify when using.
10 The shaft or sliding handle of potentiometer shall be designed as short as possible.Shaft or sliding handlelengthThe shorter the handle, the better and stable.On the contrary, the longer the shaking is, the greater the hand feel is likely to change.
11 Potentiometer carbon filmpowerIt can withstand the ambient temperature of 70 ℃, and may lose its function when the operating temperature is higher than 70 ℃.
main parameter
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The main parameters of potentiometer include nominal resistanceRated power, resolution, sliding noise, resistance variation characteristics, wear resistance, zero resistance, temperature coefficient, etc.
1) Rated power
The maximum power allowed to dissipate on the two fixed ends of the potentiometer is the rated power of the potentiometer.In use, it should be noted that the rated power is not equal to the power of the central tap and the fixed end.The rated power of potentiometer refers toalternating currentIn the road, when the atmospheric pressure is 87~107kPa, the maximum power allowed to be consumed by long-term continuous load under the specified rated temperature.The rated power series of wire wound and non wire wound potentiometers are shown in Table 2[1]。
2) Nominal resistance
The nominal resistance value marked on the product is similar to the resistance series[1]。
3) Allowable error level
The error range between the measured resistance value and the nominal resistance value can allow an error of ± 20%, ± 10%, ± 5%, ± 2% and ± 1% according to different accuracy levels.Precision potentiometerThe accuracy can reach 0.1%[1]。
4) Resistance change rule
It refers to the change relationship between the resistance value and the rotation angle (or sliding stroke) of the sliding pad contact. This change relationship can be in any functional form. The commonly used forms are linear, logarithmic and reverse logarithmic (exponential).In use, the linear potentiometer is suitable for acting as a voltage divider;Reverse logarithmic (exponential) potentiometer is suitable for volume controller in radio, recorder, record player and TV set.If similar products cannot be found during maintenance, they can be replaced by linear ones, but not logarithmic ones.The logarithmic potentiometer is only suitable for tone control[1]。
resolving power
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Potentiometerresolving powerIt is also called resolution. For a wire wound potentiometer, the output voltage will change discontinuously every time the moving contact moves for a circle. The ratio of this change to the output voltage is resolution.The theoretical resolution of the linear wirewound potentiometer is the reciprocal of the total number of turns N of the winding, and is expressed as a percentage.The more the total turns of the potentiometer, the higher the resolution.[3]
Naming and labeling methods of potentiometers
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1) The naming rule of potentiometer is the same as that of resistance, but it starts with the letter W.
2) Marking method of potentiometer: potentiometer generally adopts direct marking method, and letters and numbers are used to mark their model, nominal power, resistance value, relationship between resistance value and corner on the potentiometer shell.For example, WT - Ⅱ - 1-1k-X potentiometer is represented as a single carbon film potentiometer type II, the power is 1W, the resistance is 1k Ω, and the curve is linear[1]。
Testing and quality judgment
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The main requirements for the potentiometer are: ① the resistance meets the requirements. ②The contact between the central sliding end and the resistance body is good, and the rotation is smooth.For the potentiometer with switch, the switch part shall act accurately, reliably and flexibly.Therefore, the performance of the potentiometer must be checked before use[1]。
1) Measurement of resistance value: first, select the appropriate resistance gear of the multimeter according to the resistance value of the potentiometer to be measured, measure the resistance value, that is, the resistance value between the AC two ends, and compare it with the nominal resistance value to see whether they are consistent.At the same time, rotate the sliding contact, and its value should be fixed.If the resistance is infinite, the potentiometer is damaged.
2) Then measure the contact between the central end and the resistance body, that is, the resistance between the two ends of BC.The method is that the ohm range of the multimeter is in the proper range. During the measurement, slowly rotate the rotating shaft, and pay attention to the reading of the multimeter. Under normal conditions, the reading changes steadily in one direction. If there is any bounce, drop, or blockage, it indicates that the movable contact has poor contact.
3) When the center end slides to the head end or the end, the resistance value of the center end and the coincident end is 0 in the ideal state. In the actual measurement, there will be a certain residual value (generally based on the nominal value, generally less than 5 Ω), which is a normal phenomenon[1]。
