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What is a Potentiometer?
Also known as a potentiometer or just a pot, a potentiometer is a device used to measure an unknown voltage. It does so by comparing it with the voltage that is known. The potentiometer is a long piece of wire that is cut into several pieces, across which a conventional cell is connected. The cut pieces are placed side by side, and a thick metal strip connects the ends. The current that flows through this wire can be changed with a variable resistance known as a rheostat that is connected to the circuit.
It is possible to change the resistance manually in order to measure the potential difference. This potential difference between any two points present on a circuit is defined as the amount of work that has to be done to bring the charge from the first point on the circuit to the second point. When there is a potential difference, the current will flow in the circuit.
The potentiometer determines the internal resistance and the electric potential or the electromotive force of a given cell. It can also be used to compare the electromotive force of different cells.
The potentiometer is a three-terminal resistor with either a rotating or sliding contact that makes up an adjustable voltage divider.
What is the Working Principle of Potentiometer?
A potentiometer is an electric device that measures the electromotive force of a given cell or the internal resistance of a cell.
The basic working principle of a potentiometer is that if there is any potential drop in voltage across any section of the wire, it will be directly proportional to the entire length of the wire. However, this will only be true if the wire is of uniform cross-sectional area, and there is a uniform flow of current throughout the wire.
As mentioned above, a potentiometer has three terminals. Out of these three terminals, one is varying, and the other two are fixed. The potentiometer measures the unknown voltage by comparing it to the known voltage. The known voltage can be drawn either by a cell, or any other supply source.
When there is no potential difference between any two parts of the wire, the electrical current will continue to flow.
A potentiometer works by changing the position of a sliding contact point across the wire with uniform resistance. In a potentiometer, the input voltage has to be applied through the entire length of the resistor, while the output voltage will be the voltage drop that occurs between the sliding and fixed contact.
Since a potentiometer has two terminals of input that are fixed to the end of the resistor, in order to adjust the output voltage, you will have to move the sliding contact along with the resistor on the output side. If the electric potential of both the battery cells is the same, there will be no current circulating in the circuit, and the galvanometer will show null deflection.
This is how a potentiometer measures the voltage between two points on the uniform wire without taking any current from the actual circuit. This is why a potentiometer is said to measure voltage most accurately.
This makes the potentiometer an elementary device for comparing the electromotive force of two cells. This is also the reason why the potentiometer is ideal for calibrating a voltmeter, ammeter, and watt-metre.
How many types of potentiometers are there?
Even though the basic working principle and construction of all potentiometers are the same, there are different types of potentiometers depending on the geometry of the moving terminals. Most potentiometers comprise a wiper that rotates on a resistant material that is usually arc-shaped. In certain potentiometers, though, the wiper slides linearly along a straight resistant strip. Based on the type of resistant strip, there are two types of potentiometers, including:
- Rotary Potentiometer: This type of potentiometer has a wiper that rotates across the two terminals to vary the resistance of the spot metre. Depending on the number of times that one turns or rotates the wiper, there can be four types of rotary potentiometers:
- Single Turn Rotary Potentiometer: The wiper takes only one turn and rotates just three-fourths of the complete turn.
- Multi-Turn Rotary Potentiometer: This potentiometer can make multiple rotations, ranging from five, ten, or even more.
- Concentric Pot Rotary Potentiometer: This type of potentiometer has two pots adjusted by using concentric shafts.
- Servo Pot Rotary Potentiometer: This type of motorised pot can be used to control or adjust a servo motor automatically.
The other type of potentiometer is the linear potentiometer.
- Linear Potentiometer: Also referred to as a slide pot, fader pot, or slider, this type of potentiometer has a wiper that slides along a straight resistant strip. These can be of four different types.
- Slide Pot: Slide potentiometers are made from conductive plastics, and they are known for their superior quality.
- Dual Slide Pot: This type of potentiometer calibrates two slide pots running parallel.
- Multi-Turn Pot: This kind of potentiometer is made with a spindle, which works to actuate the slider.
- Motorised Fader Potentiometer: The movement of the wiper and the resistance in this type of potentiometer are controlled by a motor.
Conclusion
A potentiometer functions as a voltage divider and has many applications. Both linear and rotary potentiometers are used to control audio devices for controlling and changing the volume. In televisions also, potentiometers are used to control the contrast, colour, and brightness of the picture. Potentiometers are also used in designing displacement transducers due to their ability to give large output signals.
With so many applications, potentiometers still remain in use today, and these devices are used in large quantities in electronic equipment manufacturing as they provide a way to adjust electronic circuits to obtain the correct outputs.
