Potentiometer – Working principle, Types, Applications
What is a Potentiometer?
A potentiometer is defined as a 3 terminal variable resistor in which the resistance is varied manually to control the current flow.
How Does a Potentiometer Work?
A potentiometer is an electronic element. Potentiometers work by varying a sliding contact’s position through a uniform resistance. The entire input voltage is applied throughout the entire length of the resistor in a potentiometer, and the output voltage is the fall in voltage between the fixed and sliding contact as shown below.
The two output reference terminals are connected to the end of the resistor by a potentiometer. The sliding contact is moved along the output side of the resistor to adjust the output voltage.
This is different from a rheostat where one end is fixed here and the sliding terminal, as shown below, is connected to the circuit.
This is a very basic tool used to compare the emf of two cells and to calibrate the ammeter, voltmeter and wattmeter. The potentialometer’s basic working principle is quite simple. Suppose we used a galvanometer to link two batteries in parallel. The negative battery terminals are connected together and positive battery terminals are connected via a galvanometer as shown in the figure below.
Here, if both battery cells have exactly the same electrical potential, there is no circulating current in the circuit and therefore the galvanometer shows null deflection. The potentialometer’s working principle depends on this phenomenon.
Now let’s think of another circuit where, as shown in the figure below, a battery is connected through a resistor via a switch and a rheostat.
The resistor has throughout its length the uniform electrical resistance per unit length.
Therefore, the resistor’s voltage fall per unit length is the same throughout its length. Suppose we get v voltage drop per unit length of the resistor by adjusting the rheostat.
Now a typical cell’s positive terminal is attached to point A on the resistor and a galvanometer is connected to the negative terminal of the same. The galvanometer’s other end is in contact with the resistor through a sliding contact as shown in the above figure By changing this sliding edge, the galvanometer finds a point like B where there is no current, hence no deflection.
This means that emf of the standard cell is only balanced by the voltage that appears across points A and B in the resistor. Now if the distance between point A and point B is L, then standard cell emf E= Lv volt can be read.
This is how a potentiometer tests the voltage between two points (here between A and B) without removing from the circuit any current component. It is a potentialometer’s specialty, it can most precisely measure voltage.
There are two main types of potentiometers:
- Rotary potentiometer
- Linear potentiometer
While the basic building characteristics of these potentiometers vary, the working principle of these two potentiometers types is the same. Note that these are types of DC potentiometers – there are slightly different types of AC potentiometers.
The rotary type potentiometers are mainly used to obtain adjustable supply voltage to a part of electronic circuits and electrical circuits. A radio transistor’s volume controller is a popular example of a rotary potentiometer where the potentiometer’s rotary knob controls the amplifier’s supply.
There are two terminal contacts between which this type of potentiometer places a uniform resistance in a semi-circular pattern. The device also has an intermediate terminal connected to the resistance through a sliding contact with a rotary knob attached to it. The sliding contact on the semi-circular resistance can be moved by rotating the knob. The voltage is taken from a contact with the end of the resistance to the sliding contact. In short, the potentialometer is also called the POT. POT is also used to change the charging voltage of a battery in sub-station battery chargers. There are many more potentialometer rotary type uses where control of smooth voltage is required.
The linear potentiometer is exactly the same, but only the difference is that the sliding touch on the resistor is shifted linearly instead of rotating motion. Here are connected through the source voltage two ends of a straight resistor. Through a track connected along the resistor, a sliding touch could slide on the resistor. This type of potentiometer is mainly used to measure the voltage across a circuit’s branch, to measure a battery cell’s internal resistance, to compare a battery cell with a standard cell, and is commonly used in music and sound mixing systems equalizer in our daily lives.
Digital potentiometers are three terminal instruments, two fixed terminals and a wiper terminal used to change the voltage of the signal.
Virtual potentiometers have a variety of applications, including machine calibration, offset voltage change, tuning filters, screen brightness control, and volume control.
Mechanical potentiometers, however, suffer from some serious disadvantages that make it unsuitable for applications where precision is required. Some of the main disadvantages of a mechanical potentiometer are size, wiper contamination, mechanical wear, drift resistance, vibration sensitivity, humidity, etc. Digital potentiometers are therefore more popular in applications to address these drawbacks as they provide higher accuracy.
Applications of Potentiometers
A potentiometer works primarily as a voltage divider, but it is also used in many industries and applications. Categorically, some of the requirements are described below:
Pots as Controllers
Potentiometers can be used in user-controlled input applications where manual input variation is needed. Like a throttle pedal, for example, is often a dual gang bowl, used to maximize the system’s redundancy. A classic example of pot used as a user-controlled input is also the joysticks we use in computer control.
Another application in audio systems where pots are used as controllers. The logarithmic taper potentiometer is commonly used in audio volume control systems, this is because our hearing has a logarithmic response to sound stimulus. Therefore, a logarithmic taper pot would make the transition from a loud to soft sound (and vice versa) to our ears naturally smoother. For this use, a motorized pot (with logarithmic taper) is mostly used.
Pots as measuring devices
Potentiometer is most widely used as voltage measuring devices. That is the meaning of the title itself. It was first developed to calculate and monitor the voltage for the porupuse.
Since these instruments transform the wiper’s positon into an electrical output, they are used to measure distance or angles as transducers.
Pots as tuners and calibrators
In a circuit, pots can be used to tune them to obtain the desired output. A preset pot is often mounted on the circuit board during the calibration of a device as well. For most of the time, they are kept fixed.
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