A resistor is a passive component in an electrical circuit with two terminals that restrict the flow of electric current and then dissipate power when the electric current passes through it. Now a variable resistor is a three-terminal device that can adjust its current flow by the third terminal between the two terminals so that the current flow obstruction can go up and down. In simple words, you can say it is a resistor whose value of electrical resistance can be adjusted on-demand. The primary purpose of variable resistors is to control the current and voltage in an electrical circuit.
How Does a Variable Resistor Work?
As already mentioned, variable resistors are the ones whose resistance value can be controlled or adjusted according to requirements. When you slide the wiper along a resistance track which results in resistance variations, resistance can be adjusted in the present time when the circuit is being built. It can also be adjusted later on when the requirements change with the help of a knob. The variable resistor has an active resistance value that depends on where the slider contact is placed on the resistance track. Variable resistors commonly consist of a wiper contact and a resistance track. The wiper will be moved along the resistance track to adjust the adjustable component. In many resistors, you will find three main types of resistance tracks: wire wound track, cermet track, and carbon track.
The carbon and cermet tracks are more suitable for high resistance applications, whereas, for low resistance applications, the wire-wound track is suitable. You will find these resistance tracks mostly in circular shapes, but they are also available in linear forms.
Types of Variable Resistors
The types of variable resistors can be identified by the number of terminals used. On that basis, we can classify them into the following types:
Potentiometer
A potentiometer is considered an ordinary variable resistor. It operates as a potential divider and generates a voltage according to where the potentiometer is placed. They generate signals that can be used for a wide selection of applications such as measurement of the distance, amplifier gain control, etc.
Rheostat
Rheostats are very similar in construction to potentiometers; however, instead of being used as potential dividers, they are used as variable resistors. Rheostats are the resistors that use two terminals, mostly the moving and the fixed ones. One connection is formed at the end of the resistive element, whereas the other one is formed at the wiper of the variable resistor.
Rheostats have been used for a long time as power controllers connected in series with the load. But at present, they are not much preferred for the same reasons.
Digital Resistors
Digital resistors are variable resistors used when the change in resistance does not occur by mechanical movement; instead, it appears by electronic signals. They are controlled by digital protocols and can change the resistance in discrete steps. The digital protocols could be 12C and in up and down signals.
Presets
Presets are variable resistors that are small in size. They can be installed on a printed circuit board and adjusted according to the requirements. The resistance value is generally adjusted with the help of a screwdriver. Presets are more commonly used in applications consisting of an adjustable frequency tone of an alarm or adjustable frequency circuits. These are also the cheapest out of all the resistor types mentioned.
