Adjustable Variable Resistor:

Adjustable variable resistor. A resistor whose resistance can be adjusted. It is used in situations where the current of the circuit needs to be adjusted or where the resistance of the circuit needs to be changed. Adjustable variable resistor can change the characteristics of the signal generator, dim the light, start the motor or control its speed.

Adjustable variable resistor can be made of wire, sheet metal, carbon film or conductive liquid depending on their use. For general size current, metal-type Adjustable variable resistor are commonly used. In the case of low current, carbon film type is used. The electrolytic type is most suitable when the current is high; the electrodes of the adjustable variable resistor are immersed in the conductive liquid. Potentiometer is a special form of adjustable variable resistor. It balances the unknown voltage or potential and measures the unknown voltage or potential difference. The more commonly used potentiometer is simply a resistor with two fixed joints, the third connected to an adjustable brush. Another use of potentiometers is for sound control in reverberation equipment.

Classification:

Adjustable variable resistor can be divided into membrane varistors and wire-wound varistors according to their fabrication materials.

Membrane Adjustable variable resistor

Membrane Adjustable variable resistor adopts rotating regulation mode, which is generally used in small signal circuit, signal voltage and so on.

Membrane variable resistance (VR) is usually composed of resistors (synthetic carbon film), movable contacts (movable metal reeds or carbon contacts), adjusting parts and three pins (or solder plates). Two of the fixed pins are connected to the two ends of the resistor body, and the other pin (center tap) is connected to the movable contacts. The resistance between the central tap and the two fixed pins can be changed by rotating the adjusting parts and changing the contact position between the movable contact and the resistor body with a small screw screwdriver.

Membrane Adjustable variable resistor has three structures:

fully sealed, semi-sealed and non-sealed.

A. Fully sealed membrane adjustable variable resistor is also called solid variable resistor. Its resistor is made of carbon black, quartz powder, organic binder and other materials. It is pressed into the matrix of plastic or epoxy resin, and then heated and polymerized. The movable contacts are made of carbon contacts and the adjusting parts are made of plastic. Resistors and active contacts are sealed by a metal housing (with adjusting holes above the metal housing). Its advantage is that it has good dust-proof performance and seldom has bad contact failure.

B. The fabrication process of semi-sealed film adjustable variable resistor is basically the same as that of full-sealed variable resistor. The movable contact plate adopts a metal spring, and the outer plastic cover is sealed. When the plastic cover is rotated, the movable contact plate also rotates. This variable resistor is easy to adjust, but its dust-proof performance is not as good as that of the fully sealed membrane variable resistor.

C. Non-sealed membrane variable resistor is also called sheet variable resistor. Its resistor is made of carbon black, graphite, quartz powder, organic binder and other suspension, which is coated on fiberglass board or plywood board. The movable contact plate is made of metal reed with adjusting holes on the reed, without separate adjusting parts. Its shortcomings are poor dust-proof performance, easy oxidation of contacts and poor contact with synthetic carbon film.

Wire-wound Adjustable variable resistor

Wire-wound Adjustable variable resistor is a kind of power resistor. It has the advantages of low noise, high temperature resistance and high load current. It is mainly used for voltage or current adjustment of various low-frequency circuits.

High-power wire-wound adjustable variable resistor, also known as sliding-wire variable resistor, is divided into axial ceramic tube-wound variable resistor and ceramic disc-wound variable resistor, using non-sealed structure.

Low-power wire-wound adjustable variable resistor include circular vertical wire-wound variable resistors, circular horizontal wire-wound variable resistors and square wire-wound variable resistors, all of which are fully sealed packaging structures.            

In addition, varistors can be divided into vertical varistors and horizontal varistors according to their structure.