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Precision potentiometer

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 and without pointers, and the number of adjustments is 5 and 10.

Description

Type:Rotary Potentiometer
Technology:Wirewound
Resistance Tolerance:Little
Operating Temperature:55 ~+125
Total Resistance Tolerance:±5 %
Independent Linearity:±0.25 %
Feature:Solder lugs or PC pins
Operating Temperature Range:-40 °C to +125 °C

Definition

A precision potentiometer is a variable resistor that can adjust its resistance value with high accuracy.

Features

Bushing mount

Optional AR pin feature

Plastic or metal shaft and bushings

Wirewound

Solder lugs or PC pins

Sealable (Full body seal)

Designed for use in HMI applications

Function and role

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 and without pointers, and the number of adjustments is 5 and 10. In addition to the same characteristics as wire-wound potentiometers, the potentiometer also has excellent linearity, fine adjustment and other advantages, and can be widely used in the occasion of precise adjustment of resistance. The main parameters are resistance, tolerance, and rated power.

Principle and structure

Precision potentiometers come in many forms and have different structures.

1. Resistor
The resistor body is a resistance component that provides a certain resistance value in the potentiometer, and its electrical properties determine the main electrical properties of the potentiometer. The resistor body should have good resistance stability, small temperature coefficient of resistance and static noise. In order to improve reliability, it should also have the properties of moisture resistance, heat resistance, wear resistance, oxidation resistance, high load resistance and resistance to sudden changes in heat and cold.

The resistive body of the contact potentiometer, the moving contact contacts and slides on it, so the surface of the resistor has a low resistivity, which makes the contact resistance with the moving contact small; meanwhile, the surface resistivity should be evenly distributed to maintain the The change of contact resistance and track resistance within the effective electric stroke is small, and the ideal resistance law characteristics can be obtained. The surface of the resistor body should have proper smoothness, hardness and certain abrasion resistance to ensure its mechanical durability. For the wire-wound potentiometer, the resistance wire is wound on the skeleton to make a ring-shaped or spiral-shaped resistor. For the thin-film or thick-film potentiometer, the resistance film is formed on a male substrate, and the shape is mostly horseshoe-shaped and arc-shaped. Or long. For synthetic solid core potentiometers, horseshoe-shaped or strip-shaped resistance rails are molded on the base.

2. Skeleton and matrix
The skeleton is an insulating support of wire wound potentiometer resistors. The substrate (or substrate) is the support body of the non-wire-wound potentiometer resistor.
The skeleton and substrate are usually made of materials with good insulation properties, which require heat resistance, moisture resistance, good electrical insulation, good chemical stability and thermal conductivity, and only a certain mechanical strength. Generally, there are laminated paper, laminated cloth, plastic, ceramic, glass, and copper, aluminum, and aluminum alloys whose surfaces have been subjected to insulation treatment. Such metal substrates whose surfaces have been subjected to insulation treatment should have sufficient surface insulation This skeleton matrix has good heat dissipation and is easy to form.

3. Brush, sliding Q and center contact ring
In the potentiometer, the moving contact member that slides along the resistor body and draws the input voltage is called a brush <or contact-type brush into two categories: one is a metal brush. That is, brushes made of metal materials; the other is carbon brushes, that is, brushes made of mixed materials such as carbon Chenyi and tree fingers. The shape of the metal brush includes a brush shape, a dot shape, a spherical shape, and a ‘multi-finger shape. In order to ensure contact reliability and uniform current distribution, the multi-finger brush works best. The shape of the carbon brush is conical and rectangular, and the contact surface is flat and spherical. The contact reliability, low noise, mechanical durability and service life of the potentiometer are directly in contact with the brush-resistor body and the machine. Wear-related. Therefore, the brush material should have the characteristics of corrosion resistance, oxidation resistance, heat resistance and cold resistance; good thermal conductivity, good electrical conductivity, no magnetism, low contact resistance, high wear resistance and good mechanical strength. The brush and the resistor are always in contact and friction. The two materials should be matched and combined properly to obtain small contact resistance and good wear resistance. If the combination is not correct, one of the two may wear out quickly. Compared with the resistor body, the hardness and wear resistance of the brush should be slightly lower to protect the resistor body from damage and ensure its reliability. When the carbon brush is used, the resistance of the carbon brush is much larger than that of the metal brush, so it has a greater impact on the output of the potentiometer. The resistance of the carbon brush is lower than the content of carbon black and graphite in the formula. The carbon content is high and the resistance value is low, but the strength becomes poor. For the demanding carbon brushes, metal powder (such as silver powder) is sometimes added to reduce the resistance. The smaller the resistance of the carbon brush, the better, generally no more than 6 ohms. The strength of the carbon brush refers to the maximum pressure that the carbon brush can withstand. The higher the strength, the greater the pressure that can be withstood, so the contact resistance with the resistor is small.

1. Brushes made of metallic materials should have high tensile strength and good elongation, and be easy to weld and easy to process and assemble. The metal brush should use a metal material with good elasticity, so that the brush moving contact has a certain elastic pressure on the resistor. The elastic material should have a higher elastic limit, yield limit, etc. In long-term use, the smaller the elastic pressure change of the brush, the higher the contact reliability. Commonly used materials for metal brushes are: beryllium bronze, phosphor bronze, zinc white copper, silver chromium alloy, platinum nickel alloy, platinum iridium alloy, pound iridium alloy, gold silver copper alloy and so on. Alloys based on precious metals have high resistance to oxidation and corrosion, even under high temperature and high humidity conditions. When stable; contact resistance changes very little, often used in precision potentiometers.

2. Slide arm (or slider)
The sliding arm is a component that connects the rotating shaft (or sliding handle) and the brush. It moves the rotating shaft (or sliding handle) of the rotating shaft brush, driving the brush on the resistor body. The sliding arm material is selected according to the potentiometer structure. Or non-metallic materials. If an elastic metal material is selected, the sliding arm acts to apply elastic pressure to the brush; if a rigid material is used, the brush should have a certain elasticity, or another elastic part applies elastic pressure to the brush. The materials commonly used as sliding arms are cloth limbs, paper sheets, plastics, brass, silver copper and phosphor bronze. Metal materials generally require a plating protection layer.

3. Contact reed
The contact reed is a groove member connecting the brush and the current collecting member, and it transfers the electrical output of the brush to the current collecting member and leads out the Swiss. The contact reed and current collector are a kind of dynamic contact connection, so the contact reed has a great influence on the mechanical durability, contact stability and dynamic noise of the potentiometer. Therefore, the contact spring should have 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 bronze. Contact reeds are often integrated with brushes or sliding arms.

4. Rectifier and terminal
1. Current collector (also called conductive ring)
The current collector is an electrical connection member between the leading end and the contact spring. The current collector has good conductivity, small contact resistance with the contact spring, high mechanical strength and good wear resistance. Usually brass, aluminum or aluminum alloy are used; some materials need to be plated with a protective layer. The current collector of the metal glass glaze potentiometer is formed by burning a silver layer on the ceramic substrate, and the current collector of the organic synthetic solid core potentiometer can be made of low resistance conductive powder.

2. The leading end
The lead-out terminal is a component that connects the two fixed ends of the resistor body and a variable end of the brush to the external circuit. The potentiometer with switch also has the switch lead. The tapped potentiometer also has a tapped lead-out terminal, which is a lead-out wiring at a point on the effective electrical stroke. All outlets must have good electrical connections with the inside. The terminal should have good conductivity, corrosion resistance and oxidation resistance, and have certain bending, tensile mechanical strength and good weldability.
The commonly used materials for the lead-out terminal are brass and iron-nickel alloy, etc., often using electroplated nickel, tin, silver, gold, etc. as the protective layer.

5. Switch, sliding steel, screw and shaft plug
1. Rotating shaft, sliding handle, screw The rotating shaft is a component that introduces rotary motion to a rotary potentiometer; the sliding handle is a component that introduces linear motion to a straight slide potentiometer; the screw is a component that attracts multi-turn rotational motion to a screw-driven potentiometer. They are combined with other sliding contact members or rotating members to form a drive mechanism. The driving mechanism is a general term for a component that introduces mechanical motion from the outside and drives the moving contact (brush) to slide along the resistor. It is called a rotating system in a rotary potentiometer; it is called a sliding system in a direct slide potentiometer.
The shaft promises high dimensional accuracy and smoothness to ensure smooth rotation or sliding, good hand feel, and low work noise; it should also have a certain mechanical strength to ensure that no deformation or breakage occurs during the excessive transmission of the force. These components are permanently assembled with all electrical components in the potentiometer assembly towel.
These components are usually made of brass, steel, aluminum alloy, nickel-chromium steel or plastic. Shafts made of brass and steel need to be plated with a protective layer; nickel-chromium steel is corrosion-resistant and does not require a metal protective layer. It is often used in precision potentiometers; aluminum alloys also have corrosion resistance points, and are lightweight and cheap But the strength is worse than nickel-chromium steel. The use of plastic f can save metal materials, and the compression molding processing efficiency is also high, and it also has a safe function for the insulating shaft of a certain high-voltage product.

2. Shaft sleeve
The shaft sleeve is an ampoule that maintains precise and dynamic coordination with the rotating shaft (or screw), and it can form a whole rest member with the base. Generally, the threaded bushing also functions as a mounting part. In the fast potentiometer, the ball bearing b is used, which has high precision, low friction and long rotation life.
The sleeve material should be easy to publish. The inner hole has high dimensional accuracy and sufficient mechanical strength. Brass, steel, and aluminum alloys are commonly used. Some require electroplated protective layers. Insulating sleeves are also made of plastic.

Six, the base and the protrusion
1. Base (also called base)
The base is the basic part for installing and supporting components such as resistors, lead-out consumers and current collectors. The base is usually made of ceramic, plastic or metal materials. The ceramic base is commonly used for metal glass glaze, metal film and high-power wire-wound potentiometer; the base of precision wire-wound potentiometer is usually aluminum alloy. Plastic is easy to process into various shapes, mechanical and electrical properties, “and low price, light weight and corrosion resistance, so it is widely used in organic synthetic solid core, synthetic carbon film and general wire wound potentiometer.
The base and bushing are usually tightly pressed or riveted together. Sometimes the metal blue plate is pressed into the base to improve the heat dissipation capacity of the potentiometer. Some potentiometer bases and substrates are an integral component, such as organic synthetic solid potentiometers.

2. Shell
The shell is the shell that encapsulates and protects the main components of the potentiometer. It plays a role in protecting the internal components and preventing dust and moisture. The metal shell is also commonly used for grounding and shielding to suppress interference from external electric fields.
The shell should have the characteristics of high mechanical strength, corrosion resistance and moisture resistance. For enclosures that require grounding shielding, apply a solderable metal material or ammonium layer.
Common shell materials include brass, steel, aluminum alloy and plastic.

7. Stop
The stop is a device used to limit the travel of the drive mechanism. The stop usually cannot exist independently. It can be integrated with the housing or the base, or with the first flow member or the outlet.

8. Switch
A switching device with a switching potentiometer is a device driven by the potentiometer’s shaft to turn the power on and off. There are many forms of switches, and the common ones can be divided into three types: dial rotary, spring rotary and push-pull.
The structure of the strong head rotary switch is that the rotating shaft drives the insulated cam, and the cam makes the dial pinch high, so that the switch changes from the on position to the off position. The structure of the spring rotary switch is that the rotation of the shaft drives the pendulum block. One end of the spring is connected to the pendulum block and the other end is linked to the contact piece. disconnect. These two kinds of switches have a small passing current, and the materials can be zinc white copper, phosphor bronze, copper chromium alloy, etc. Each switch must turn the potentiometer to zero position, so the actual service life of the potentiometer is reduced. These two types of potentiometers with switches often use single-pole single-throw and are suitable for low-current and low-voltage electronic instruments, such as general semiconductor radios. The structure of the push-pull switch is that when the shaft is axially pulled out or pushed inward, the slider is slid or reset by the action of the spring, so that the contact rod and the two contacts are quickly connected or disconnected. The contact reliability of this switch is good. Using silver-jin or silver-tungsten alloy, it can resist arc, and the switch allows larger current to pass. The potentiometer can be opened and closed by axial push-pull action at any adjusted position, so when it is used repeatedly, there is no need to adjust the potentiometer, which is very beneficial to prolong the service life of the potentiometer. This switch is generally a double-pole double-throw type, suitable for TV sets and high-end Ji Ji.

Nine, rubber band
The rubber ring is a component that plays a sealing role in the potentiometer to prevent the intrusion of moisture. It is often placed between the rotating shaft and the sleeve, the casing and the base, and the drive mechanism and the casing. When used between the rotating shaft and the shaft sleeve, it also plays a role in increasing the starting force; torque and making the rotating torque uniform. For sealed potentiometers, 2-3 rubber bands are often placed between the rotating shaft and the sleeve to improve the sealing performance

Application

Widely used in electronic equipment, used for volume control in audio and receiver.

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