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Internal structure and functional use of precision potentiometer
2022-07-11

Precision potentiometer, also called precision adjustable potentiometer, is a variable resistor that can adjust its own resistance with high precision. There are forms with pointers, without pointers, etc., and the adjustment circles are 5 circles, 10 circles and so on. In order to help you understand in depth, this article will summarize the relevant knowledge of precision potentiometers. If you are interested in what this article is about to cover, keep reading.

The role of precision potentiometers

1. Act as an inductor or capacitor under high frequency signals. (Related to external circuit characteristics) Inductors are mainly used to deal with EMC problems.

2. When the parameters of the matching circuit are uncertain, use 0ohm instead. When debugging theoretically, confirm the parameters and replace them with components with detailed values.

3. When wiring, assuming that the real cloth cannot be passed, you can also add a 0ohm resistor (I think it should be a straight plug, not a surface mount.

4. When measuring the current consumption of a certain part of the circuit, you can remove the 0ohm resistor and connect an ammeter to measure the current consumption.

5. There is no function in the circuit, just for debugging convenience or compatible design on the PCB.

6. It is used as a jumper. If a certain line is not used, the resistance can be directly subsidized.

Internal structure and functional use of precision potentiometer

Function and use of precision potentiometer components

1. Resistor

The resistor body is a resistor component that provides a certain resistance value in a precision potentiometer, and its electrical properties determine the main electrical properties of the potentiometer. The resistor body generally has good resistance value stability, small resistance temperature coefficient and quiet noise. In order to improve reliability, it also has the properties of moisture resistance, heat resistance, wear resistance, oxidation resistance, high load resistance and thermal shock resistance.

Brushes, sliding Q and center contact ring.

In the potentiometer, the movable contact member that slides along the resistor body and draws out the input voltage is called a brush or a contact-type input brush. There are two categories: one is a metal brush. That is, brushes made of metal materials; the other type is carbon brushes, which are brushes made of mixed materials such as carbon and tree fingers. The shapes of metal brushes are brush-shaped, point-shaped, spherical-shaped and multi-fingered. In ensuring contact reliability and uniform current distribution, multi-fingered brushes are the best. The shapes of the carbon brushes are conical and rectangular, and the contact surfaces are flat and spherical. The contact reliability, low noise, mechanical durability and service life of the potentiometer are directly related to the contact state and mechanical properties of the brush-resistor body. wear related. The brush and the resistor body are always in contact and friction state. The two materials should be properly matched and combined to obtain low contact resistance and good wear resistance. If the combination is not appropriate, one of the two may wear out quickly. Therefore, the brush material has the characteristics of corrosion resistance, oxidation resistance, heat resistance and cold resistance; good thermal conductivity, good electrical conductivity, non-magnetic, low contact resistance, high wear resistance and good mechanical strength.

2. Skeleton and matrix

The skeleton is the insulating support for the resistor body of the wirewound potentiometer. The base (or substrate) is the support for the resistor body of the precision wirewound potentiometer.

The skeleton and the matrix are usually made of materials with good insulating properties, requiring heat resistance, moisture resistance, good electrical insulation, good chemical stability and thermal conductivity, and only a certain mechanical strength. Generally, there are laminated paper rubber sheets, laminated cloth quilt sheets, plastics, ceramics, glass, and copper, aluminum and aluminum alloys with insulating surfaces. The skeleton matrix has good heat dissipation and is easy to form.

3. Contact reed

The contact reed is a groove piece connecting the brush and the current collector, which transmits the electrical output of the brush to the current collector and the lead-out. The contact reed and the current collector are connected by a moving contact, so the contact reed has a great influence on the mechanical durability, contact stability and dynamic noise of the potentiometer. Therefore, the contact spring generally has good elasticity to ensure a certain elastic pressure on the current collector, it also has good electrical and thermal conductivity, and its hardness and wear resistance should match the current collector. Commonly used materials are phosphor bronze and quilt bronze. Contact reeds are often integrated with brushes or sliding arms.

4. Leads and current collectors

1. Pinout

The lead-out end is a component that connects the two fixed ends of the resistor body and a variable end of the brush to the external circuit. Precision potentiometers with switches also have switch leads. The tap potentiometer also has a tap terminal, which is the lead wire at a certain point on the effective electrical stroke. All leads and internals should have good electrical connections. The terminal should have good electrical conductivity, corrosion resistance and oxidation resistance, as well as certain bending resistance, tensile mechanical strength and good weldability.

2. Current collector The current collector is the electrical connection member between the lead-out end and the contact spring. The current collector has good electrical conductivity, small contact resistance with the contact spring, high mechanical strength and good wear resistance. The current collector of the metal glass glaze precision potentiometer is formed by sintering the silver layer on the porcelain substrate, and the current collector of the organic synthetic precision solid potentiometer can be pressed with low-resistance conductive powder.

5. Base and housing

1. Pedestal

The base is the basic part for installing and supporting parts such as the resistor body, the lead-out resistor and the current collector. The base is usually made of ceramic, plastic or metal material. Ceramic bases are commonly used for metal glass glaze, metal films and high-power wire-wound potentiometers; aluminum alloys are commonly used for the bases of precision wire-wound potentiometers. Plastic is easy to be processed into various shapes, mechanical and electrical properties, low price, light weight and corrosion resistance, so it is widely used in organic synthetic solid core, synthetic carbon film and general precision wire wound potentiometers.

2. Shell

The shell is the shell that encapsulates and protects the main components of the precision potentiometer, and it plays the role of protecting the internal components and preventing dust and moisture. The metal casing is also commonly used for grounding and shielding to suppress the interference of the external electric field.

6. Switch, sliding steel, screw and shaft plug

1. The shaft, the sliding handle and the screw shaft are the components that the rotary potentiometer introduces into the rotary motion: the sliding handle is the component that the straight-sliding potentiometer introduces to the linear motion; the screw is the component that the screw-driven potentiometer introduces to the multi-turn rotary motion. They are combined with other sliding contact members or rotating members to form a drive mechanism. The drive mechanism is a general term for the components that introduce mechanical motion from the outside to drive the movable contact (brush) to slide along the resistor body. It is called a rotating system in a rotary potentiometer; it is called a sliding system in a straight-sliding potentiometer.

The shaft has high dimensional accuracy and smoothness to ensure smooth rotation or sliding, good hand feel and low power noise. It also has a certain mechanical strength to ensure that it will not deform and break when the transmission force is too high.

2. Bushing

The shaft sleeve is in the fast precision potentiometer with the rotating shaft, and the ball bearing is used for high precision, low friction and long rotation life. An ampoule that maintains a precise dynamic fit, it can form a whole resting member with the base. Generally, the threaded bushing also acts as a mounting member.

This article will introduce this. In addition to the same characteristics of the wire wound potentiometer, the potentiometer also has the advantages of excellent linearity and fine adjustment. It can be widely used in the occasion of precise adjustment of the resistance. The main parameters are: Resistance, tolerance, rated power. Widely used in electronic equipment for volume control in audio and receivers.


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