A potentiometer is an electrical component that provides variable resistance, and is often user-controlled. The linear variety of this component allows for gradual changes in resistance at a linear proportionality of mechanical input to electrical output.
Two types of potentiometers with different tracks are available. These are Linear (Lin) or Logarithmic (Log) tracks.
Linear and Logarithmic Potentiometer
- A linear potentiometer provides changes in resistance that is linearly proportional to the distance between the contact slider and the ground terminal.
- A graph of the percentage output verses the slider distance would show a straight, gradually increasing line that changes at set intervals.
- With linear potentiometers, the resistance between one end of the track and the wiper varies at a constant rate as the slider is moved along the track.
- In logarithmic types, the change in resistance is much less at one end of the track to the other.
- Logarithmic potentiometers are used as volume controls in audio equipment because the response of the human ear to the loudness of sound is also logarithmic.
Uses of Linear Potentiometers
- Linear potentiometers are used in audio equipment as source faders.
- They are also commonly found in cathode ray tube devices that allow for user-controlled adjustment of the electron beam characteristics.
- The are found in the display options on an analog television.
Types of Potentiometer
The Potentiometer or POT is manufactured by using different types of materials like carbon composition, cermet, metal film, and conductive plastic.
Different types of potentiometers are intended for specific applications and environments. For instance, some industrial, heavy-duty models must be able to withstand extreme temperatures up to 150°C.
Wire wound potentiometers
Construction
- This potentiometer comprises of several rounds of wire wound around the shaft of the non-conducting material.
- The turns of the coil are bonded together by an adhesive. In this case the slider, connected to the body whose displacement is to be measured, moves on the potentiometer track and it makes contacts with successive turns of the coil.
- In this case the wire between the two successive turns is not covered by the slider, which limits the resolution of the wire wound potentiometers. However, the larger the number of turns of the coil, more is the resolution of the coil.
- The resolution is measured as the reciprocal of the number of turns of the coil. This devise has low noise and is mechanically rough and tough.
Specifications
- Resistance value : 10Ω to 100KΩ
- Current rating : 1 A to 20 A
- Power rating : upto 3W
- Temperature rating : 100o C
Applications
- It is used to control voltage in the circuit.
- It can be used as a volume controller for radio receivers, TV receivers etc.
- They are also used in measuring instruments.
Carbon Composition Potentiometers
Construction
- The carbon composition potentiometers are formed by depositing carbon composition ink on an insulating body, which in most of the cases is phenolic resin.
- This is one of the most commonly used materials for the pots that is quite cheap and has resolution better than the wire wound potentiometers.
- They have reasonable life and tolerable noise levels.
Specifications
- Resistance Range : 100Ω-1MΩ
- Total Resistance Tolerance : ±2%, ±5%, ±10%
- Power Rate(70oC) : upto 0.6W
- Working Voltage : 160V
- Rotational Life Expectancy : 10000 Cycles
- Temperature rating : 70o C
Applications
- It is used in TV, tape recorder, PA system, radio as a volume controller.
- It is used in measuring instruments such as CRO.
- They are also used in high frequency applications.
