A variable resistor consists of a track that provides the resistance path. The two terminals of the machine are connected to both the ends of the track. The third terminal is associated with a wiper that decides the motion of the track. The motion of the wiper throughout the track helps in increasing and decreasing the resistance. Microhm Electronics'  NRS series can be made to variable resistor.

 

The track is generally made of a mixture of ceramic and metal or can be made of the carbon as well. As the resistive material is required, a carbon film type of variable resistors is generally used. They find applications in the radio receiver circuits, audio amplifier circuits, and TV receivers. The rotary track resistor has two applications: one is to modify the resistance and the other – the switch method – which is is used for the electric contact and non-contact by the on/off operation of the switch. There is a switch method in which variable resistors with the annular cross-section are used for controlling the equipment. The track made in a straight path is called a slider. As the position of the slider cannot be seen or confirmed according to the modification of resistance, a stopping mechanism is generally integrated to prevent the hazards caused due to over-rotation.

A Variable Resistor can be used mostly in two different ways. When one end of the resistance track and wiper terminal is connected with the circuit, then-current through the resistor limits according to the position of the wiper contact on the resistance track. As the wiper contact slides away from the connected end of the resistance track, the resistive value of the resistor increases and current goes down through the circuit-which means, the variable resistor behaves like a rheostat.

 

Another use is as a potentiometer. In this case, the two ends of the resistance track are connected with a voltage source. Hence, the voltage drop across the resistance track is equal to the value of the voltage sources. Now the output or load circuit is connected across one end of the resistance track and wiped terminal. Hence, the voltage across the load terminals is the fraction of source voltage and it depends upon the position of the wiper terminals on the resistance track. This is another widely used application of variable resistors. Potentiometers are used to control voltages, whereas rheostats are used to control electric currents.
 

 

Variable Resistors can be found in audio control, televisio, motion control, transducers, computation, home electrical appliances, and oscillators. Variable resistors include a variable resistor chip, variable resistor potentiometer, 12-volt variable resistor, digital variable resistor, high power variable resistor or trimmer resistor. Microhm Electronics attaches importance to the development of varibale resistors.