Resistors consist of two terminals and generate resistance to the flow of current. In this blog, we will be covering variable resistors, a type of resistor that is utilized for adjusting circuit resistance to control voltage or current in an electronic circuit.
The electrical resistance within variable resistors is varied by sliding a wiper contact along a resistance track. In some cases, resistance can be modified to a preset value when the circuit is being constructed by adjusting a screw attached to it or by a controlling knob connected to it. The active resistance value relies on the position of the slider contact on the resistance track.
A variable resistor primarily consists of a resistance track and a wiper contact. The wiper contact moves the length of the resistance track when the adjustable component is adjusted. There are three main types of resistance tracks used in variable resistors, these including carbon tracks, cermet tracks, and wire-wound tracks. Carbon tracks and cermet tracks are typically used for high-resistance applications while wire-wound tracks are implemented in low-resistance variable resistors. In most cases, resistance tracks are circular, but a straight track can also be utilized. The next section will cover a few different types of variable resistors.
The first is a potentiometer which is the most common among the other types. This type of variable resistor is paired with a potential divider, which is used to generate a voltage signal depending on the position of the potentiometer. The potentiometer consists of three terminals, two of which are fixed and one is changeable. The two fixed terminals are connected to both ends of the resistive track and the third terminal is affixed to the wiper. The resistance of the potentiometer changes as the wiper moves along the resistive path. Some common applications of potentiometers include the measurement of distance or angles, tuning of circuits, and amplifier gain control.
The next type of variable resistor is a rheostat. A rheostat is a current controlling device and is similar in construction to potentiometers. They consist of two terminals, one connected at the end of the resistance track and the other to the wiper. By turning the spindle, the resistance changes between the two terminals from zero up to the maximum resistance. Rheostats are used in circuits to perform tuning or calibration. For example, they can be used to control the luminosity of a lamp or the rate of charging a capacitor.
The last type that will be covered is a thermistor. A thermistor has a resistance that changes when the surrounding temperature changes. They come as either negative temperature coefficient (NTC) thermistors or positive temperature coefficient (PTC) thermistors. The resistance of NTC thermistors decreases as the temperature increases while the resistance of the PTC thermistors increases as the temperature increases.
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