What is variable resistor
Variable resistors, as the name implies, are resistors whose resistance is able to be varied, whether manually or automatically.Manual Variable resistors consist of a resistance track with connections at both ends and a wiper which moves along the track as you turn the spindle. The track may be made from carbon, metal mixture or a nichrome wire.
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| Fig: 1 |
Adjustable resistor used in applications that require the adjustment of current or the varying of resistance in an electric circuit. The rheostat can adjust generator characteristics, dim lights, and start or control the speed of motors. Its resistance element can be a metal wire or carbon, depending on the application. For average currents, the metallic type is most common; for very small currents, the carbon type is used, Variable resistors are often called potentiometers.
Common types of manual variable resistor are Preset and V/C or T/C potentiometer.See Fig: 1 (Symbols of variable Resistors)
Different types of Variable Resistor
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| Preset (Horizontal type) |
Preset
A preset is a three legged variable resistor. They are designed to be mounted directly onto the circuit board.The resistance is varied by adjusting the rotary control over it. The adjustment can be done by using a small screw driver or a similar tool.The variable resistance is obtained across the single terminal at front and one of the two other terminals. The two legs at back offer fixed resistance which is divided by the front leg. So whenever only the back terminals are used,a preset acts as a fixed resistor. Presets are specified by their fixed value resistance.
Potentiometer
Variable resistors used as potentiometers have all three terminals connected
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