Home  Potentiometer

Jun 18 2020

Common Potentiometer Types and Applications Available

Ⅰ Introduction

A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider, also commonly known as pot. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat. The mechanical construction of potentiometers is very similar, each usually composed of a resistor and a rotating or sliding system, that is, a moving terminal (known as the wiper) and a resistive strip (also known as a track) to obtain a partial voltage and current output. For different requirements, there are many types of potentiometer in electronics.

What is a Potentiometer? How does a potentiometer work? Find out in this episode of potentiometers basics.

Catalog

Ⅰ Introduction

Ⅱ Types of Potentiometers Avalable and Classification Criteria

Ⅲ Common Potentiometers Introduction & Application

3.1 Types of Potentiometers

3.2 Typical Application: Potentiometer Sensor

Ⅳ Potentiometer Using Tips

Ⅴ Question Related to Potentiometer and Going Further

5.1 Question

5.2 Answer


Ⅱ Types of Potentiometers Available and Classification Criteria

There are two main types of potentiometer, linear potentiometer and rotary potentiometer, which belong to adjustable potentiometer.

Types of Potentiometers Image

Table 1. Common Types of Potentiometer

Potentiometer Type

Classification Criteria

According to resistor material

It can be divided into the wire wound, synthetic carbon film, metal glass glaze, organic solid core and conductive plastic potentiometer. The electrical performance mainly depends on the material used. In addition, there are potentiometers made of metal foil, metal film and metal oxide film, which used in a special purpose.

According to the working environment

 

Based on the working environment, there are universal, high-precision, high resolution, high resistance, high temperature, high frequency, high power potentiometers and so on.

According to the adjustable resistance

For the adjustable resistance, 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 effect of the moving contact of the brush on the resistor body on the performance and life of the potentiometer, there are non-contact potentiometers, such as photo potentiometers and magneto potentiometers.

According to the construction

Rotary type: Common form, the usual rotation angle is about 270~300 degrees.

Single turn: Common form

Multi-turn: For occasions requiring precise adjustment

Linear sliding: Usually used in the mixer, to immediately see the position of the sound volume and do fade control.

 

According to the number

 

Single connection: One rotary only controls a potentiometer.

Duplex: Two potentiometers are controlled by a rotary, mainly used in dual channels, which can control two sound channels at the same time.

According to resistance and rotation angle

Linear type: The change in resistance value is linearly related to the rotation angle or moving distance.

Logarithmic type: The change in resistance value is logarithmic with the rotation angle or moving distance. The main application of this type of potentiometers is sound volume control.

According to the adjustment method

 

Potentiometers can be divided into rotary potentiometers, push-pull potentiometers, sliding potentiometers, etc. according to the adjustment method.

According to the actuation way

Potentiometers can be divided into manual potentiometers and electric potentiometers according to the actuation.

Other

Rotary switch potentiometer: it usually used to combine the sound volume switch and the power switch, that is, turn it counterclockwise to the bottom to cut off the sound switch and turn off the power.


 

Ⅲ Common Potentiometers Introduction & Application

3.1 Types of Potentiometers

  • Rheostat

Rheostat

The potentiometer can be used as a three-terminal component or a two-terminal component. Rheostat is a kind of potentiometers, which can adjust the resistance value, and the current can be adjusted in the circuit. As time goes by, The term "rheostat" is becoming obsolete, with the general term "potentiometer" replacing it. The general rheostat is composed of a wire (resistance wire) with a larger resistance and a device that can adjust the contact point to control the effective length of the resistance wire. Rheostat functions: 1. Limit the current and protect the circuit; 2. Change the voltage distribution in the circuit.

 

  • Rotary Potentiometers

Rotary Potentiometer

The internal structure of the rotary potentiometer is shown in the figure. The main features include a saddle-shaped resistor made of a metal film or a carbon film, a movable arm, a sliding end (also known as a contact or a electric brush), a spin axis, a rotating handle, and a soldering terminal. The resistance between the A and C is the total resistance of the potentiometer. One sliding end is connected to B, and the other end is in close contact with the resistor. When the position of the sliding end changes, the resistance between A-B and B-C changes, with a tolerance of 10% to 20%. Some potentiometers are also equipped with switches, which can be turned on and off by turning the handle. The rotation angle of the ordinary potentiometer is 270°, and the resistance value cannot be finely adjusted.

The rotary potentiometers are used mainly for obtaining adjustable supply voltage to be a part in electronic circuits and electrical circuits. For example, rotary potentiometer is mainly used for telecommunication products, car amplifiers, multimedia audio, smart home appliances, etc. Its functions are: sound volume adjustment, light intensity adjustment, menu selection, speed adjustment, temperature adjustment, etc.

 

  • Logarithmic Potentiometers

Logarithmic Potentiometer

When the logarithmic potentiometer starts to rotate, the closer the rotation angle is to the end of the maximum resistance value, the greater the resistance value change. The resistance value changes according to the logarithmic relationship of the rotation angle. This type of potentiometer is mostly used in the instrument and is also suitable for tone control circuits. The conductive material on the resistor body of this potentiometer is unevenly distributed. When begins to rotate, the resistance value changes greatly; when the rotation angle increases, the change in resistance is small. The change in resistance is in a logarithmic relationship with the rotation angle of the potentiometer. Because the human ear's perception of volume is roughly in a linear relationship with the logarithm of sound power, that is, when the sound increases from small, the human ear feels very sensitive, but when it reaches a certain value, even if the sound power has increased greatly, the human feels a little changed. It can be seen that the change rule of the resistance value of the logarithmic potentiometer is more in line with the characteristics of the human ear hearing. Therefore, in the volume control circuit of the radio and TV, the logarithmic potentiometer can be a better choice.

 

  • Linear Potentiometers

Linear Potentiometer

Linear potentiometers also known as slide pot, slider, or fader. It is a kind of potentiometers that the brush moves along the linear path. When the sliding contact of the linear potentiometer rotates, the relationship between its resistance and rotation angle changes according to a linear rule. It is used to linearly adjust the voltage in the circuit. Its output voltage is linearly related to the rotation angle of the potentiometer. This type of potentiometer is mainly used to measure the voltage on the branch of the circuit, measure the internal resistance of the battery, compare the battery with the standard battery and so on. In addition, it is usually used in the sound mixing system in the equalizer. When the frequency division ratio of the potentiometer must be proportional to the rotation angle, a linear potentiometer can also be used.

 

  • Digital Potentiometers

Digital Potentiometer

Digital potentiometer is a new type CMOS integrated circuit, which mix digital and analog signal processing to replace traditional mechanical potentiometer (analog potentiometer). The digital potentiometer is controlled by a digital input and produces an analog output. Depending on the digital potentiometer, the maximum tap current can be from a few hundred microamperes to a few milliamperes. Digital potentiometers adjust the resistance value by numerical control. It has the obvious advantages of well flexibility, high adjustment accuracy, no contact, low noise, sound performance, anti-vibration, anti-interference, small size, long service life, etc. In addition, digital potentiometers generally have a bus interface, which can be programmed through a single-chip microcomputer or logic circuit. It is suitable for forming various programmable analog devices, such as programmable gain amplifiers, programmable filters, programmable linear voltage-stabilized power supplies, tone/volume control circuits, and the simulation function block of the single-chip microcomputer control system.

 

  • Membrane Potentiometers

Membrane Potentiometer

The resistor body is formed by coating carbon black, graphite, quartz and other materials on the surface of the substrate. The process is simple, and membrane potentiometer is currently the most widely used potentiometer. It is characterized by high resolution, good wear resistance and long life. Its disadvantages include current noise, large nonlinearity, poor moisture resistance and poor resistance stability.

It should be noted that in order to prevent the burning of the contacts and the deterioration of conductive layers of the membrane potentiometer, the working current of the small resistance potentiometer shouldn’t exceed the maximum current allowed by the contact. Avoid using it in the environment with large chemical concentration, to prolong the service life of the potentiometer.

 

  • Wirewound Potentiometers

Ceramic Wirewound Potentiometer

It has the advantages of high precision, good stability, small temperature coefficient, reliable contact, high temperature resistance, and strong power load capacity. The disadvantage is that the resistance range is limit, the high frequency performance is poor, the resolution is not high, and the high resistance wirewound potentiometer is easy to break, the size is large, and the price is high. The resistor body of the wirewound potentiometer is composed of a resistance wire wound on an insulation. There are many types of resistance wire. The material of the resistance wire is selected according to the structure of the potentiometer, the resistance value and the temperature coefficient, etc. The thinner the resistance wire, the greater the resistance value and resolution in a given space. But it is easy to break, which affects the device life. For application, wirewound potentiometers are widely used in electronic instruments and meters.

 

  • Synthetic Carbon Film Potentiometers

It has the characteristics of wide resistance range, good resolution, simple tech process and low price, but it has large dynamic noise and poor moisture resistance. This type of potentiometer should be used as a functional potentiometer, which is widely used in consumer electronics. In addition, the printing process can mass the production of carbon film.

There are common synthetic carbon film potentiometers, small synthetic carbon film potentiometers with switches, single-connection potentiometer, duplex potentiometer, duplex non-shaft potentiometer potentiometer(with switch), small precision synthetic carbon film potentiometer, push-pull switch synthetic carbon film potentiometer, sliding synthetic carbon film potentiometer, precise multi-turn synthetic carbon film potentiometer, etc.

 

  • Organic Solid State Potentiometers

The solid state potentiometer is made by mixing and heating carbon black, graphite, quartz powder, organic binder and other prepared materials, pressing them on a plastic substrate, and polymerizing them by heating. Its resistance range is wide, the resolution is high, the heat resistance is good, the overload capacity is strong, the wear resistance is good, and the reliability is high, but the moisture resistance is poor. This type of potentiometer is generally made into a small semi-fixed form, which is used for micro-transfer in the circuit.

 

  • Metal Glaze Potentiometers

It not only has the advantages of organic composition solid potentiometer, but also has a small temperature coefficient of resistance (similar to wirewound potentiometer), but it has large dynamic contact resistance and large equivalent noise resistance, so 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 shock has been improved greatly, and it can work reliably under harsh environmental conditions.

 

  • Conductive Plastic Potentiometers

Have the advantages of wide resistance range, high linear accuracy, strong resolution, and particularly long wear life. Although its temperature coefficient and contact resistance are large, it can still be used to automatically control in the instruments.

 

  • Multi-turn Potentiometers

In some industrial control and instrument circuits, high precision is usually required. Multi-turn potentiometer is a potentiometer to meet the production needs. This type of potentiometer has many advantages. Multi-turn potentiometers allow for a rotation angle of more than 360 degrees of mechanical travel from one end of the resistive track to the other.

 

3.2 Typical Application: Potentiometer Sensor

Among all position sensors, the most commonly used is a potentiometer, because it is an economical and easy to use “position sensor".

Linear Position Sensor Image

It has a sliding contact connected to a mechanical shaft, which can be rotating (angular) or sliding (linear) in moving process, which causes the resistance value between the slider and the connection at both ends to change, resulting in electricity. The actual tap position of the signal output on the resistance trace is proportional to its resistance value. In other words, the resistance is proportional to the position. There are two types of potentiometer position sensors are as examples introduced below.

 

3.2.1 Resistance Position Sensor

Resistance position sensors, sometimes referred to as a potentiometer or a position converter, include linear and rotary type. They were originally developed for military applications and are widely used in radios, televisions or control panel adjustment knobs and so on.

Such a potentiometer doesn’t need additional power and circuit support, so it is a passive device. The potentiometer has two working modes: voltage divider and variable resistor. When used as a variable resistor, its resistance changes with the position of the sliding end, using one fixed end and a sliding end when working. When it is employed to voltage divider, it is the most common use of potentiometer. The output reference voltage is obtained by dividing the resistive components. The physical position of the sliding end can be obtained according to the voltage division theory of the series resistance and the opposite output voltage.

Figure 1. Simple Position Sensor Circuit

Simple Position Sensor Circuit

It includes an operational amplifier circuit and potentiometer position sensor, and the output voltage reflects the position of the sliding end.

 

Potentiometers are used as position sensors in many cases. It has two fixed ends and a sliding end, and the sliding end is connected to the outside through a mechanical transmission shaft. The motion model can be the linear or the rotary. When the sliding end moves, it will change the resistance between the two fixed ends. The output voltage is usually proportional to the displacement of the sliding end, or the resistance of the sliding end and the fixed end is proportional to the displacement.

There are many sizes and types of potentiometers, and the most commonly used include two categories: rotary and linear. When used as a position sensor, it's sliding end is usually connected to the detected object. During working, a fixed reference voltage needs to be applied to the two fixed terminals of the potentiometer. The voltage is output from the sliding terminal and a fixed terminal, that is, the output voltage is related to the position of the sliding terminal.

 

3.2.2 Capacitance Position Sensor

The capacitance position sensor is a non-contact type position sensor, usually composed of three parts: the detection area, the protective layer, and the casing. They can measure the precise position of the target, but only the object can be conducted. If the measured object is not conductive, measuring the thickness or density of the object is still useful.

When measuring a conductive object, the output signal has nothing to do with the material of the object, because all conductors are the same electrode for the capacitance position sensor. This sensor is mainly used in disk drives, semiconductor technology, and high-precision industrial measurement, but the requirements of the accuracy and frequency response of the sensor are very high. When used to measure non-conductors, capacitance position sensors are often used to detect labels, coating, and paper or film thickness measurement.

Capacitance position sensors were originally used to measure linear displacement distances, ranging from a few millimeters to a few nanometers, using the electrical property of conductivity to complete the measurement. The ability of an object to store charge is called capacitance. A commonly used capacitor device for charge storage is a plate capacitor. The capacity of the plate capacitor is proportional to the electrode area and dielectric constant, and inversely proportional to the distance between the electrodes. So when the distance between the electrodes changes, the capacitance also changes. In short, capacitance position sensors use this property to complete position detection.

A typical capacitance position sensor includes two metal electrodes, with air as a dielectric. One electrode of the sensor is a metal plate, the other electrode of the capacitor by the detected conductive object. When a voltage is applied between the conductor plates, an electric field is established between the plates, and the two plates store positive and negative charges, respectively. Capacitance position sensors usually use an alternating voltage, which causes the charge on the plates to change polarity regularly, thus the change in target position can be detected by measuring the capacitance values between the two plates.

The capacitance is determined by the plate space, the dielectric constant of the dielectric, and the plate distance. In most sensors, the area and dielectric constant of the electrode plate will not change, only the distance will affect the capacitance between the electrode and the target object. Therefore, the change in capacitance can show the target position. Through correction, the output voltage signal of sensor is linearly related to the distance between the detection plate and the target. This is the sensitivity of the sensor. It reflects the ratio of the output voltage change to the position change. The unit is usually 1V/micrometer, in other words, the output voltage changes by 1V for every 100 microns.

When voltage is applied to the detection space, a diffuse electric field will be generated on the detected object. In order to reduce the interference, a protective layer is added. It applies the same electromotive force at both ends of the detection area, preventing leakage of the electric field in the detection space. The conductors outside the other detection areas will form an electric field with the protective layer, which will not interfere with the electric field between the target and the detection area. Owing to the presence of the protective layer, the electric field in the detection area has a conical shape. The projected area of the electric field emitted by the detection electrode is 30% larger than the detection area. Therefore, there must be at least 30% larger diameter area of the detected object than the sensor detection area, which is important for sensor standard correction.

Compared with other non-contact type position sensors, capacitance potentiometer sensors have the advantages of high resolution, low price, and wide detection range. But when the detection environment is very dry or humid, and the sensor probe is far away from the detection target, this sensor is no longer applicable.

Different Types of  Potentiometer

Ⅳ Potentiometer Using Tips

1) Resistors of potentiometers are mostly made of polycarbonate synthetic resin. Avoid contact with the following items: ammonia, amines, alkaline aqueous solutions, aromatic hydrocarbons, ketones, lipid hydrocarbons, chemicals with high acid value, etc., otherwise device performance will be affected.

2) Potentiometer terminals should avoid the use of water-compatible fluxes, otherwise they will cause chemical reactions between metal oxidation and other materials. Avoid the use of inferior fluxes, because poor soldering may cause problems, resulting in poor contact or open circuit.

3) If the welding temperature is too high or the time is too long when the terminals of the potentiometer are soldered, the potentiometer may be damaged. Pin-type terminals should be 235 ℃ ± 5 ℃ when welding, welding should be more than 1.5MM away from the potentiometer body, do not use solder to flow through the circuit board when soldering; solder wire terminals should be 350 ℃ ± 10 ℃ when welding. And the terminal should avoid heavy pressure, otherwise it is easy to cause poor contact.

4) When soldering, the flux should be avoided from entering the potentiometer, otherwise it will cause poor contact between the brush and the resistor, resulting in noise.

5) The potentiometer is best used in the voltage adjustment structure, and the current adjustment structure should be avoided, because the contact resistance between the resistor and the sliding arm is not good for the passage of large currents.

6) Avoid condensation or water droplets on the surface of the potentiometer, and avoid putting it in a humid place to prevent device degradation or short circuit.

7) When installing the rotary potentiometer, the strength should not be too tight to damage the screw teeth or cause poor rotation, etc.; when installing sliding potentiometers, avoid using too long screws, otherwise it may influence the sliding handle even directly damages the potentiometer itself.

8) In the process of putting the potentiometer on the knob, the pushing force used should not be too large, otherwise it may cause damage to the potentiometer.

9) The rotational force (rotation or sliding) of the potentiometer will become smaller as the temperature increases, and strengthener as the temperature decreases. If the potentiometer is used in a low-temperature environment, it needs to be explained so that a special low-temperature grease can be used.

10) The design of the potentiometer shaft or slider should be designed as short as possible. The shorter the length of the shaft or slider, the better the equipment Conversely, the longer the shaking, the greater the interference.

11) The power of the carbon film of the potentiometer can withstand the surrounding temperature of 70 ℃. When the use temperature is higher than 70 ℃, it may lose its function.

 

5.1 Question

What's the main types of potentiometers?

 

5.2 Answer

There are two main types of potentiometer, linear potentiometers and rotary potentiometers. Membrane Potentiometers are another type of potentiometer they are often referred to as “soft pots” and can be either linear or rotary.

Related Articles

0 comment

Leave a Reply

Your email address will not be published.

 
 
   
Rating: