A potentiometer is a type of variable resistor. It is usually composed of a resistor body and a rotating or sliding system, that is, a moving contact is moved on the resistor body to obtain a partial voltage output.
A potentiometer is a resistance element with three lead-out terminals whose resistance can be adjusted according to a certain change law. A potentiometer usually consists of a resistor and a movable brush. When the brush moves along the resistor body, a resistance value or voltage having a certain relationship with the amount of displacement is obtained at the output end.
The potentiometer can be used as a three-terminal element or a two-terminal element. The latter can be regarded as a variable resistor. Because its role in the circuit is to obtain an output voltage that has a certain relationship with the input voltage (external voltage), it is called a potentiometer.
The key parts that make up a potentiometer are resistors and brushes. Potentiometers can be classified into several types according to their structural form and whether they have switches.
Potentiometers can also be classified according to the material of the resistor, such as wire-wound, synthetic carbon film, metallic glass glaze, organic solid core and conductive plastic. The electrical performance is mainly determined by the materials used. In addition, there are potentiometers made of metal foil, metal film and metal oxide film for resistors, which have special applications. Potentiometers are distinguished according to their characteristics, including universal, high-precision, high-resolution, high-impedance, high-temperature, high-frequency, high-power potentiometers; according to the resistance adjustment method, there are adjustable, semi-adjustable and fine-tuning The latter two are also called semi-fixed potentiometers. In order to overcome the adverse effects of the brush’s moving contact on the resistor on the performance and life of the potentiometer, there are non-contact non-contact potentiometers, such as photosensitive and magnetic potentiometers, for a small number of special applications.
Wire-wound potentiometer: It has the advantages of high accuracy, good stability, small temperature coefficient, reliable contact, etc., and high temperature resistance and strong power load capacity. The disadvantages are that the resistance range is not wide enough, the high-frequency performance is poor, and the resolution is not high. Moreover, the high-resistance wire-wound potentiometer is easy to break, the volume is large, and the price is high. This potentiometer is widely used in electronic instruments and meters. The resistance body of a wire-wound potentiometer is composed of a resistance wire wound on an insulator. There are many types of resistance wires. The material of the resistance wire is selected according to the structure of the potentiometer, the space to accommodate the resistance wire, 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 it is easy to disconnect during use, which affects the life of the sensor.
Synthetic carbon film potentiometer: It has the characteristics of wide range of resistance value, good resolution, simple process, low price, etc., 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. The printing process can be used to automate the production of carbon diaphragms.
Organic solid core potentiometer: Wide resistance range, high resolution, good heat resistance, strong overload capacity, good wear resistance, high reliability, but poor hot flash resistance and dynamic noise. This type of potentiometer is generally made into a small semi-fixed form, which is used for micro-calling in the circuit. Metal glass glaze potentiometer not only has the advantages of organic solid potentiometers, but also has a small resistance temperature coefficient (similar to wire-wound potentiometers), but 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, and it can work reliably under harsh environmental conditions.
Conductive plastic potentiometer: wide range of resistance value, high linear accuracy, strong resolution, and particularly long wear life. Although it has a large temperature coefficient and contact resistance, it can still be used in analog and servo systems in automatic control instruments.
Digital potentiometer: Potentiometer made by integrated circuit technology; a string of resistors is integrated into a chip, and a MOS tube is used to connect the resistor in series with the public terminal; the control accuracy is determined by the number of bits controlled, generally 8 bits, 10 bits, 12 bits, etc .; can be used in analog circuits for impedance matching, amplification loop control, etc .; avoids the trouble of jitter adjustment operation; and provides a convenient way for the device’s automatic gain, voltage change, impedance matching, etc.
Multi-turn precision adjustable potentiometer: In some industrial control and instrument circuits, high adjustable precision is usually required. 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 and other advantages.
Classification of resistance materials Carbon Film: Uses a carbon film as the resistance film. Metal Film: A special ceramic gold (cermet) film made of a mixture of ceramic and metal materials is used as the resistance film. Wirewound: Made of metal wirewound as a resistor. Compared with carbon film or porcelain gold film, it can withstand larger power.
Structural classification Rotary: common form. The usual rotation angle is about 270 ~ 300 degrees. Single-turn: a common form. Multi-turn type: used for occasions where precise adjustment is required. Linear sliding type: usually used in the mixer, it is easy to immediately see the volume position and fade control.
Quantity classification Single type: one shaft controls only a single potentiometer. Dual type: two potentiometers are controlled by the same shaft, which is mainly used in two channels, and can control two channels at the same time.
Classification of resistance value change scale Linear scale type: The change of resistance value has a linear relationship with the rotation angle or moving distance. This type of potentiometer is called a B-type potentiometer.
Logarithmic scale formula: The change of resistance value has a logarithmic relationship with the rotation angle or moving distance. The main purpose of this type of potentiometer is volume control, of which the A-type potentiometer is commonly used. For low-volume occasions; In addition, there is a C-type potentiometer with a logarithmic scale in the opposite direction.
Classification by resistor material Potentiometers can be divided into two types: wire-wound potentiometers and non-wire-wound potentiometers according to the material of the resistor. Wire-wound potentiometers can be divided into general-purpose wire-wound potentiometers, precision wire-wound potentiometers, high-power wire-wound potentiometers, and preset wire-wound potentiometers. Non-wirewound potentiometers can be divided into solid potentiometers and membrane potentiometers. The solid potentiometer is divided into organic synthetic solid potentiometer, inorganic synthetic solid potentiometer and conductive plastic potentiometer. The film potentiometer is divided into carbon film potentiometer and metal film potentiometer.
Classification by regulation Potentiometers can be divided into rotary potentiometers, push-pull potentiometers, and straight-slip potentiometers according to the adjustment method.
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 rule of resistance value.
Classified by structural characteristics Potentiometers can be divided into single-turn potentiometers, multi-turn potentiometers, single-link potentiometers, double-link potentiometers, multiple-link potentiometers, tapped potentiometers, switch potentiometers, locking potentiometers, Unlocked potentiometers and patch potentiometers.
Classification by driving method The potentiometer can be divided into manual adjustment potentiometer and electric adjustment potentiometer according to the driving method.
Other special types Potentiometer with switch: Usually used to combine the volume switch with the power switch, that is, turn it counterclockwise to the bottom to cut off the switch and turn off the power.
The main functions of the potentiometer in the circuit are as follows 1. Used as a voltage divider The potentiometer is a continuously adjustable resistor. When the rotary or sliding handle of the potentiometer is adjusted, the movable contact slides on the resistor body. At this time, at the output of the potentiometer, an output voltage having a certain relationship with the applied voltage of the potentiometer and the angle or stroke of the movable arm can be obtained.
2. Used as a rheostat When the potentiometer is used as a rheostat, it should be connected as a two-terminal device, so that a smooth and continuously changing resistance value can be obtained within the stroke range of the potentiometer.
3. Used as a current controller When the potentiometer is used as a current controller, one of the selected current output terminals must be a sliding contact output terminal.