Potentiometer

A potentiometer is a three-terminal resistor in which the resistance varies according to the flow of electric current. It is used as an alterable voltage divider. It has a rotating or a sliding contact which is used to adjust the voltage driver. Although it has three terminals, only two of them are useful. One of the terminals acts as a rheostat or variable resistor.

The potentiometer is a voltage divider that is used to measure electric potential (voltage). Generally, potentiometers are used to control electrical devices. Potentiometers can also be used as position transducers if they are operated by a particular mechanism, for example, in a joystick. Since the power disappears in the potentiometer; therefore, potentiometers are rarely used to control notable power directly. Johann Christian Poggendorff described the method to measure potential difference or voltage via a potentiometer. Further, this method became a standard laboratory measuring technique.

A potentiometer is described as an instrument used for measuring the electromotive force of two cells by stabilizing it against the potential difference. The potential difference is produced by passing a current through a variable resistance. The major potentiometer types are the rotary potentiometer and linear potentiometer.

Although both types of potentiometers are constructed differently, they work on the same principle. These two types of potentiometers mentioned above are DC potentiometers. AC Potentiometers are a little different from the DC ones. 

The primary role of a potentiometer is:

• To compare the EMF of a standard cell with a battery cell.
• To measure the internal resistance of a cell.
• To measure the voltage across a circuit.

Working of a potentiometer

A potentiometer is an electronic instrument that works when the position of the sliding contact is varied across a uniform resistance.

Working principle of a potentiometer

The working principle of a potentiometer is that the potential across a wire is directly proportional to its length, provided with the constant current. The wire should have a uniform cross-sectional area. If there is no potential difference found between the two notes, the electric current will flow. 

Potentiometer types

There are two major types of potentiometers:

1. Rotary potentiometer
2. Linear potentiometer

Although the construction processes of these two, potentiometers are different, they work on the same principle. Let us understand the application and working of the rotary potentiometer and linear potentiometer in detail.

• Rotary potentiometers

The major use of the rotary type potentiometers is to provide an adjustable supply voltage to electric circuits and a part of an electronic circuit. Rotary potentiometers use the zero reflection method, due to which there is no chance of getting errors. The primary example of a rotary potentiometer is the volume controller of a transistor. The radio transistor controls the supply to the amplifier.

Rotary potentiometers have two terminals, in between the two terminals, a uniform resistance is placed. The uniform resistance is placed in a semi-circular position. The rotary knob is connected to the resistance, which is attached to a middle terminal present on a rotary potentiometer. So when the knob is rotated, the sliding contact on the semi-circular resistance moves. The rotary potentiometer has several uses; some of the major applications are listed below:

• It is used in substation battery chargers to alter its charging voltage.
• It is used to measure the inner resistance of a cell.
• It finds use in comparing the EMF of two cells.
• It measures small EMFs, as rotary potentiometers are highly sensitive.

• Linear potentiometers

The linear potentiometers are quite similar to the rotary potentiometers, but the major difference is that the sliding contact gets moved instead of rotary movement linearly on the resistor. A linear potentiometer has two ends on a straight resistor connected across the source voltage. The sliding terminal is connected to an end of the output circuit and the resistor terminal is connected to the other end of the circuit. 

Linear potentiometers have versatile applications. It is used to measure the voltage across a circuit and measure a cell’s internal resistance. In our day-to-day life, linear potentiometers are used in a part of the sound mixing system, that is, the equalizer.

The linear potentiometer has several industrial uses; some of the major applications are listed below:

• Agricultural machinery
• Industrial processing
• Industrial machinery
• Mobile vehicles
• Medical
• Motorsport
• Robotics

Applications of a potentiometer

There are several uses of a potentiometer; the major applications of a Potentiometer are described below:

• It is used as a voltage divider.
• It can be used as a receiver for controlling the volume of television (TV) or radio.
• A potentiometer is also used to control linearity.
• Potentiometers are used in several medical types of equipment.
• It is also used to operate wood processing machines.
• Used in injection mold machines.
• Potentiometers are used as a controller for many functional pieces of equipment.
• It is used to compare the EMF between standard cells and battery cells.
• It is used to measure the internal resistance of a battery cell.
• Used to measure the voltage across a Circuit.

Conclusion: 

The basic principle of the potentiometer functioning can be described as – the voltage on the wire directly proportional to the distance. It can be described as V = IR. The potentiometer works based on the voltage across the wire and its length, which has a uniform cross-sectional area with constant flow. This is an inverse proportionality relationship.