Home > Knowledge > Content
What is a variable resistor ​
Dec 14, 2017

What is a variable resistor


Variable resistor, also known as adjustable resistor, the text symbol with the letters "R" or "RH" said.


Variable resistor is usually used in the need for regular adjustment (that is, the resistance does not require frequent changes in the circuit), adjust voltage, adjust the current or signal control and other functions, the main parameters and fixed resistors are basically the same.


Variable resistor type and structure.


Variable resistors according to the production of materials can be divided into film-type variable resistors and wire-wound variable resistors; by structure can be divided into vertical variable resistors and horizontal variable resistors.


1. Variable resistor film variable resistor rotary adjustment method, generally used in small signal circuits, adjust the bias voltage or bias current, signal voltage and so on.


Film variable resistor usually consists of a resistor (synthetic carbon film), movable contact (movable metal reed or carbon contact), regulating components and three pins (or solder) and so on. Two of the fixed pins are connected to both ends of the resistor, and the other pin (center tap) is connected to the movable contact. Rotate the adjusting screw with a small flat screw to change the contact position between the movable contact and the resistor to change the resistance between the center tap and the two fixed pins.


Film variable resistors are all sealed, blue sealed and unsealed three structures.


The hermetically sealed film type variable resistor is also called a solid type variable resistor. The resistor body is made of carbon black, quartz powder, organic binder and the like, and is pressed into the matrix of materials such as plastic or epoxy resin , And then heated polymerization. Active contacts with carbonaceous contacts, conditioning components made of plastic. The resistor body and the movable contact are sealed by the metal case (adjustment hole above the metal case). The advantage is dust-proof performance, rarely poor contact failure.


Semi-hermetically sealed variable resistor resistor body and hermetically sealed variable resistor resistor making process is basically the same. The movable contact piece adopts the metal reed and the external plastic cover cover, and when the plastic cover is rotated, the movable contact piece also rotates. This variable resistor is easy to adjust, but the dustproof performance is not as good as hermetically sealed variable resistors.


Non-hermetically sealed film type variable resistor is also called chip adjustable resistor. The resistor is made of carbon black, graphite, quartz powder, organic binder, etc. as a suspension and coated on glass fiber board or bakelite board Into The movable contact piece is made of metal reed, there is adjustment hole on the reed, no separate adjusting part is set separately. The disadvantage is poor dustproof, easy contact oxidation, prone to poor contact with the synthetic carbon film failure.


2. Wirewound variable resistor Wirewound variable resistor belongs to the power type resistor, with the advantages of low noise, high temperature, large carrying current, etc. It is mainly used for voltage or current adjustment of various low frequency circuits.


High-power wire-wound variable resistor, also known as sliding rheostat, which is divided into axial porcelain tube-wound variable resistor and porcelain wire wound variable resistor, non-sealed package structure.


Low-power wirewound variable resistors are round vertical wirewound variable resistors, circular horizontal wirewound variable resistors and square wirewound variable resistors, etc., are all sealed package structure .