Structural characteristics of commonly used potentiometers

(1) Synthetic carbon film potentiometer: It is the most used potentiometer at present. The resistor body is made of a mixture of carbon black, graphite, quartz powder, organic binder, etc., which is coated on a glue board or a glass fiber board.

Advantages: high resolution, wide resistance range;

Disadvantages: large sliding noise, poor heat and humidity resistance.

Varieties: There are ordinary synthetic carbon film potentiometers, small synthetic carbon film potentiometers with switches, single-joint potentiometers with switches (without switches), double-joint coaxial potentiometers without switches (with switches), and double-joint different shafts without switches ( With switch) potentiometer, small precision synthetic carbon film potentiometer, push-pull switch synthetic carbon film potentiometer, straight sliding type synthetic carbon film potentiometer, precision multi-turn synthetic carbon film potentiometer, etc.

(2) Metal film potentiometer: The resistor body is made of metal alloy film, metal oxide film, metal composite film, and tantalum oxide film material deposited on the ceramic substrate by vacuum technology.

Advantages: high resolution, lower sliding noise than synthetic carbon film potentiometers;

Disadvantages: small resistance range, poor wear resistance.

(3) Wire-wound potentiometer: its resistance body is made of resistance wire wound on a metal or non-metal plate coated with insulating material.

Advantages: high power, low noise, high precision and good stability;

Disadvantages: poor high frequency characteristics.

Varieties: There are ordinary wire-wound potentiometers, ordinary multi-turn wire-wound potentiometers, precision multi-turn wire-wound potentiometers, straight-sliding precision multi-turn wire-wound potentiometers, functional precision multi-turn wire-wound potentiometers, etc.

(4) Solid potentiometer: It is made of carbon black, graphite, quartz powder, organic binder and other materials after mixing and heating, pressing on the plastic substrate, and then heating and polymerizing.

Advantages: high resolution, good wear resistance, wide resistance range, high reliability, small size;

Disadvantages: loud noise, poor high temperature resistance.

Variety: It can be divided into small solid potentiometer, linear solid potentiometer, logarithmic solid potentiometer.

(5) Single-turn potentiometer and multi-turn potentiometer:

Single-turn potentiometer: its sliding arm can only be rotated within a range of less than 3600, which is generally used for volume control;
Multi-turn potentiometer: For each turn of its shaft, the contact of the sliding arm only changes a small distance on the resistor body. When the sliding arm changes from one extreme position to the other, the shaft needs to rotate several times. Generally used in precision regulation circuits.

(6) Single potentiometer and double potentiometer:

Single potentiometer: a group of potentiometers are controlled by an independent shaft;
Double potentiometer: Usually, two potentiometers with the same specifications are installed on the same shaft. When the shaft is adjusted, the sliding contacts of the two potentiometers rotate synchronously. There are also some double potentiometers that are asynchronous and different axes.

(7) Potentiometer with switch: A switch device is attached to the potentiometer. The switch is coaxial with the potentiometer, and the movement and control methods of the switch are divided into two types: rotary type and push-pull type.

Uses: It is mostly used for volume control and power switch in black and white TV sets. Small rotary potentiometer with switch is mainly used for volume control (or current and voltage regulation) and power switch in semiconductor radios or other small electronic products.
Type: Switch positions include SPST, SPDT and DPST.

(8) Straight-sliding potentiometer: its resistance body is a rectangular bar, and it changes the resistance value through the linear motion of the sliding handle connected to the sliding seat.
Uses: Generally used for volume control or balance control in TVs and stereos.

(9) SMD potentiometer: Also known as chip potentiometer, it is an ultra-small linear potentiometer without a manual rotating shaft. Tools such as screwdrivers are required for adjustment.

Type: divided into 1. Single-turn potentiometer;
2. Multi-turn potentiometer - It is a precision potentiometer, with vertical and horizontal structures.

(10) Stepping potentiometer: It is composed of a stepping motor, a rotating shaft resistor, and a moving contact. The movable contact can be adjusted manually through the rotating shaft, and can also be driven by a stepper motor.

Uses: mostly used for volume control in audio power amplifiers.

Structural characteristics of commonly used potentiometers

Potentiometer

A potentiometer is an adjustable resistor and one of the most widely used components in electronic circuits. It has three external terminals, two of which are fixed terminals and the other is a center tap. Turn or adjust the potentiometer's rotating shaft, and the resistance between the center tap and the fixed end will change. 2.2.1 Performance index of potentiometer

The performance indicators of potentiometers and resistors have the same meaning in terms of nominal resistance, allowable deviation, rated power, etc., in addition to the following indicators.

1. Resistance change law

The change law of resistance value refers to the relationship between the rotation angle (or stroke) of the potentiometer and the output voltage when it is used as a voltage divider. The resistance change law of common potentiometers is linear change type, exponential change type, logarithmic change type.

2. sliding noise

When the brush slides on the resistor body, the voltage between the center end and the fixed end of the potentiometer fluctuates irregularly. This phenomenon is called the sliding noise of the potentiometer. It is caused by the uneven distribution of the resistivity of the material and the irregular change of the contact resistance when the brushes slide.

3. resolution

Finest adjustment of output volume achievable. Wirewound potentiometers have poor resolution.

4. limit voltage

The highest voltage a potentiometer can withstand for a short period of time.

5. Mechanical durability

It is usually marked by the number of times of rotation (or sliding), which is an indicator of the service life of the potentiometer.

2.2.2 Several common potentiometer models and specifications

1. Organic Solid Core Potentiometer

The resistance powder is made of conductive material, organic filler and thermosetting resin. After hot pressing, a solid core resistance body is formed on the base. The potentiometer is characterized by simple structure, high temperature resistance, small size, long life and high reliability. The performance indicators of several commonly used organic solid-core potentiometers are shown in Table 2-6.

Table 2-6 Performance indicators of commonly used organic solid-core potentiometers

2. Wirewound Potentiometer

The resistance body is formed by winding the alloy resistance wire on the insulating frame, and the reed of the center tap slides on the resistance wire. Wirewound potentiometers are widely used, and can be made into ordinary, precision and fine-tuning potentiometers, and have relatively large rated power, small temperature coefficient of resistance, low noise and high withstand voltage. The performance indicators of commonly used wire wound potentiometers are shown in Table 2-7.

Table 2-7 Performance indicators of commonly used wire wound potentiometers

3. Synthetic Membrane Potentiometer

A layer of synthetic carbon film is coated on the insulating base, heated and polymerized to form a carbon film, and then combined with other parts. This type of potentiometer has continuous resistance change, high resolution, wide resistance range and low cost. However, the adaptability to temperature and humidity is poor, and the service life is short. The performance indicators of commonly used synthetic membrane potentiometers are shown in Table 2-8.

Table 2-8 Performance indicators of commonly used synthetic membrane potentiometers

4. Multi-turn potentiometer

Multi-turn potentiometers are precision potentiometers. It is divided into with pointer, without pointer and other forms, the number of adjustment circles are 5 circles, 10 circles and so on. The potentiometer has the same characteristics as the wire wound potentiometer, but also has the advantages of excellent linearity and fine adjustment, which can be widely used in the occasion of precise adjustment of resistance.