Ⅰ. The structure of the potentiometer
A potentiometer consists of a resistive element, a sliding contact (wiper) that moves along the element, making good electrical contact with a portion of the element, electrical terminals at each end of the element, and a means to move the wiper from one end to the other organization. and a housing containing the filter element and wiper.
Many cheap potentiometers have a resistive element made into an arc, usually less than a full turn, and a wiper (C) that slides over that element as it is turned to make electrical contact. The resistive elements can be flat or angled. Each end of the resistive element connects to terminals (E, G) on the case. The wipers are usually connected to the third terminal (F), between the other two terminals. On panel potentiometers, the wiper is usually the center terminal of the three. For single-turn potentiometers, the wiper is usually less than one revolution around the contact. The only entry point for contamination is the narrow space between the shaft and the axis of rotation.
The resistive elements of cheap potentiometers are usually made of graphite. Other materials used include resistance wire, carbon particles in plastic, and ceramic/metal hybrids called cermets. Conductive track potentiometers use conductive polymer resistor pastes that contain wear-resistant resins, polymers, solvents, and lubricants in addition to the carbon that provides electrical conductivity.
Multi-turn potentiometers can also be operated by rotating the shaft, but in a few turns rather than less than a full turn. Some multi-turn potentiometers have a linear resistive element with a sliding contact moved by a lead screw. Others have a helical resistive element and a wiper that makes 10, 20 or more complete turns and moves as the helix turns. User-accessible and preset multi-turn potentiometers allow for finer adjustments; turning the same angle typically changes the setting by one-tenth that of a simple rotary potentiometer.
A string potentiometer is a multi-turn potentiometer operated by an attached spool that is turned by a metal wire to overcome a spring, allowing it to convert linear position into a variable resistor.
Ⅱ. Classification of potentiometers
1. Classification of resistance value change scale
Logarithmic scale: the change of the resistance value has a logarithmic relationship with the rotation angle or moving distance. The main purpose of this kind of potentiometer is volume control. Among them, the A-type potentiometer is commonly used, which is suitable for large volume in the clockwise direction and large volume in the counterclockwise direction. For the occasion of small volume; in addition, there is a C-type potentiometer whose logarithmic scale change direction is opposite to that of A-type. The resistance value of a logarithmic scale potentiometer varies logarithmically with the position of the slider. This means that the actual resistance value does not change linearly as the slider slides from one position to another, but follows a logarithmic curve.
This design makes the potentiometer more in line with human hearing perception, because the human ear's perception of volume is also logarithmic. Logarithmic scale potentiometers are mainly used for volume adjustment. In audio systems, by using a logarithmic potentiometer, the user can achieve finer control in the lower volume range and a larger adjustment range in the higher volume range.
Linear scale type: the change of resistance value is linear with the rotation angle or moving distance, this kind of potentiometer is called B-type potentiometer.
2. Classification of resistor materials
Carbon film type: Carbon film potentiometer is a common type of potentiometer, which is coated with a layer of carbon film on the resistance element to realize the adjustment of resistance value. It uses a carbon film as a resistive film. The sliding terminal changes the resistance value of the potentiometer by sliding on the carbon film. The position of the wiper determines the resistance value, which affects circuit performance. The accuracy of carbon film potentiometers is usually in the medium range and is suitable for general electronic applications. Accuracy depends on manufacturing process and design and is usually within a few percent. Carbon film potentiometers can be knob (round) or slide (linear). Knob potentiometers require a knob to be turned, while slide potentiometers require a slide terminal to slide along the length of the resistive element.
Porcelain gold film: use a special porcelain gold film made of a mixture of ceramic and metal materials as the resistance film. The resistance element of the porcelain gold film potentiometer is composed of a thin metal film coated on the porcelain substrate. The thickness of the metal film is very thin, usually between a few microns and tens of microns. Porcelain gold film potentiometer has high precision and stability. The metal film provides a relatively uniform and stable resistance characteristic, making the performance of the potentiometer more stable under changes in time and temperature. Porcelain gold film potentiometers are widely used in electronic equipment and instruments that require high precision and stability, such as test instruments, medical equipment, aerospace systems, etc. They are also commonly used in applications that require frequent adjustments or prolonged use because their stability reduces post-adjustment variation.
Wire-wound type: use metal wire wound as a resistor, which can withstand higher power than carbon film or porcelain gold film. , whose resistance element is composed of filaments or coils wound on an insulating core. The resistance element of the wire-wound potentiometer is wound on an insulating core by a thin wire or a coil, usually using a metal wire, such as a nickel-chromium alloy. The winding method and density of the filament can affect the power handling capability, accuracy and resolution of the potentiometer. Wirewound potentiometers usually have a high power handling capability, which makes them suitable for some applications that need to withstand high current or high power, such as motor control, power regulation, etc. Since the resistance element is composed of a wound metal coil, the wire-wound potentiometer has high precision and stability. Their resistive properties remain relatively stable over time and temperature.
3. Structural classification
Single-turn type: It is a common type of potentiometer. Its knob or sliding terminal only needs to turn or slide one turn to complete the adjustment of the entire resistance value range. The general rotation angle is about 270-300 degrees. The knob or sliding terminal of the single-turn potentiometer only needs to turn or slide one turn to complete the adjustment of the entire resistance value range. The accuracy of single-turn potentiometers is usually in the general range, suitable for most applications that do not require high precision. Because the adjustment process of single-turn potentiometers is relatively simple, they are suitable for scenarios where quick adjustment of resistance values is required, such as volume control in audio equipment. Because the adjustment process of single-turn potentiometers is relatively simple, they are suitable for scenarios where quick adjustment of resistance values is required, such as volume control in audio equipment.
Multi-turn type: is a type of potentiometer whose knob or slider needs to be turned or slid multiple turns to complete the adjustment of the entire range of resistance values. Multi-turn potentiometers are highly accurate because their adjustment range is divided into turns, allowing for finer and more precise resistance adjustments within each turn. Multi-turn potentiometers generally have a larger adjustment range because the multiple turns provide more room for variation in resistance value.
This makes multi-turn potentiometers suitable for applications requiring a wide range of adjustment. Since the adjustment process requires multiple turns or slides, multi-turn potentiometers are particularly suitable for applications that require fine adjustment, such as laboratory instruments, precision measuring equipment, etc. Multiturn potentiometers are often used in applications that require high accuracy, stability, and reliability, such as test instruments, medical equipment, aerospace systems, and more.
Rotary type: also known as knob potentiometer, is a common type of potentiometer whose adjustment operation is realized by turning a knob. A knob can be connected to the sliding terminal of a potentiometer, thereby changing the resistance value of the potentiometer. Rotary potentiometers operate by turning a knob. The rotation of the knob will change the position of the sliding terminal on the resistance element of the potentiometer, thereby changing the resistance value of the potentiometer.
The accuracy of the rotary potentiometer is usually in the general range, which is suitable for most applications that do not require high accuracy. Rotary potentiometers can be multi-turn or single-turn designs. Multi-turn potentiometers need to be rotated multiple times to complete the adjustment of the entire resistance range, while single-turn potentiometers only need to be rotated once.
Linear sliding type: also known as sliding potentiometer, is a type of potentiometer whose sliding terminal can slide along the length of the resistive element, thereby changing the resistance value of the potentiometer. Linear slide potentiometers operate by sliding a sliding terminal. The position of the wiper determines the resistance value of the slide potentiometer, which affects circuit performance. Linear slide potentiometers are widely used in various electronic devices and circuits, especially in applications that require linear sliding operation. They are usually used in scenarios that require basic resistance adjustments, such as audio volume control, brightness control, position control, etc.
4. Classification of adjustment methods
Push-Pull: is a special type of potentiometer that combines rotary and push-pull operation with additional functionality. This type of potentiometer typically has a knob for rotary adjustment and a push-pull button for additional operations, such as switching functions or modes. Push-pull potentiometers usually have a push-pull button attached to the center or next to a knob. The knob is used to rotate to adjust the resistance value, while the push-pull button is used to perform additional operations, such as toggle switch, mode selection, etc. The additional push-pull button of the push-pull potentiometer makes it versatile. They can perform other functions while the resistance is adjusted, reducing the number of control elements on the device.
Straight-sliding type: called a linear sliding potentiometer or a sliding rheostat, it is a type of potentiometer whose sliding terminal can slide linearly along the length of the resistive element, thereby changing the resistance value of the potentiometer. The operation method of the slide potentiometer is realized by sliding a sliding terminal. The position of the wiper determines the resistance value of the slide potentiometer, which affects circuit performance.
5. Other special forms
Value Display Potentiometer: It is a special type of potentiometer integrated with a digital display or indicator, which can display the current resistance value of the potentiometer or the value of the adjustment parameter. Value display potentiometers typically have high precision and accuracy, making them suitable for applications requiring precise monitoring. Value display potentiometers are widely used in scenarios that require accurate monitoring and display of resistance values, such as laboratory measurement, industrial control, medical equipment, etc. Traditional potentiometers require external measuring equipment to determine their resistance value, while value display potentiometers integrate adjustment and display functions, simplifying the operation process. There are different types of value display potentiometers, including knob type, sliding type, multi-turn type, etc., and the appropriate type should be selected according to the needs of specific applications.
Trimmer potentiometer: also known as adjustment potentiometer or trimming potentiometer, is a potentiometer specially designed for fine adjustment of resistance value. Trimmer potentiometers are designed to provide small adjustments in resistance value, usually within a narrow range. Trimmer potentiometers are usually high-precision to ensure that small adjustments can accurately reach the desired resistance value. Trimmer potentiometers may be physically similar to regular potentiometers, but are usually designed with more precision and fine-tuning capabilities in mind. They have smaller sizes and finer adjustment mechanisms. Since the trimmer potentiometer requires small adjustments, it is usually necessary to use special adjustment tools, such as screwdrivers, nut wrenches, etc., in order to perform fine adjustments accurately.
Slide potentiometer: Also known as a slide rheostat, is a type of potentiometer whose sliding terminal slides along the length of the resistive element, thereby changing the resistance value of the potentiometer. Slide potentiometers are typically used in applications that require a straight line sliding operation. Also called a sliding rheostat, a type of potentiometer whose sliding terminal can slide along the length of the resistive element, thereby changing the resistance value of the potentiometer. Slide potentiometers are typically used in applications that require a linear slide operation
Thumbwheel Potentiometer: Is a special type of potentiometer, usually used to manually adjust the resistance value. Thumbwheel potentiometers can easily adjust the resistance value by turning the knob or wheel with fingers, so it is suitable for applications that require frequent manual adjustment of the resistance value. Because thumbwheel potentiometers can precisely adjust resistance values, they are often used for digital setup, calibration, and debugging, such as adjusting the initial value of a counter or setting the range of a measuring instrument. Thumbwheel potentiometers typically have a compact design for limited panel space. Some thumbwheel potentiometers have a digital display or indication to show the current resistance value or adjustment parameter for enhanced visibility.
Ⅲ. Precautions for potentiometer
1. Avoid using water capacitive flux when soldering the terminals of the potentiometer, otherwise it will promote metal oxidation and moldy materials; avoid using inferior flux, poor soldering may cause difficulty in tinning, resulting in poor contact or open circuit.
2. The resistor body of the potentiometer is mostly made of polycarbonic acid synthetic resin, and should avoid contact with the following items: ammonia water, other amines, alkaline aqueous solution, aromatic hydrocarbons, ketones, lipid hydrocarbons, Strong chemicals (high pH), etc., otherwise it will affect its performance.
3. Avoid condensation or water droplets on the surface of the potentiometer, and avoid using it in a humid place to prevent insulation deterioration or short circuit.
4. The potentiometer is best used in the voltage adjustment structure, and the wiring method should choose "1" pin to be grounded; the current adjustment structure should be avoided, because the contact resistance between the resistor and the contact piece is not conducive to the passage of large currents.
5. In the process of putting the potentiometer on the knob, the thrust used should not be too large (cannot exceed the parameter index of the push-pull force of the shaft in the "Specifications"), otherwise it may cause damage to the potentiometer.
6. The shaft or sliding handle of the potentiometer should be designed as short as possible. The shorter the shaft or slider length, the better the feel and stability. On the contrary, the longer the shake, the bigger the shake, and the hand feel is easy to change.
Ⅳ. Potentiometer testing and judging whether it is good or bad
Measurement of resistance value: First, according to the resistance value of the potentiometer under test, select the appropriate resistance gear of the multimeter, measure the resistance value, that is, the resistance value between the two ends of the AC, and compare it with the nominal resistance value. are consistent. At the same time turn the sliding contact, its value should be fixed. If the resistance is infinite, the potentiometer is broken.
Then measure the contact between the central end and the resistor body, that is, the resistance value between the two ends of BC. The method is that the ohm gear of the multimeter is in the appropriate range. During the measurement process, slowly rotate the shaft and observe the readings of the multimeter. Under normal conditions, the readings change steadily in one direction. Bad contact failure.
When the center end slides to the head end or the end, ideally the resistance value of the center end and the overlapping end is 0. In actual measurement, there will be a certain residual value (generally depending on the nominal value, generally less than 5Ω), which is a normal phenomenon .
Ⅴ. Terminology of potentiometer
1. Sliding pot or sliding pot: A potentiometer that is usually adjusted by sliding the wiper left or right (or up and down depending on the installation) with your finger or thumb.
2. Trimmer Pot or Trimmer Pot: A trimmer usually means an electrical signal that is adjusted once or is not commonly used for "trimming".
3. Thumb Pot or Thumbwheel Pot: Small rotary potentiometer, infrequently adjusted by the little thumbwheel.
Ⅵ. The relationship between potentiometer and switch
The potentiometer is a component that can adjust the resistance value, and the
switch is a component used to control the on-off of the circuit.
Some audio equipment uses components that combine the functions of potentiometers and switches. For example, some volume controls may include a knob-style potentiometer that the user can turn to adjust the volume, while when the knob is pressed, it may trigger a switch action for the mute function.
Some switches may be combined with potentiometers to toggle between different modes or settings. For example, in some devices, turning a potentiometer can adjust different parameters, and pressing a knob can switch to a different mode.
