WHAT IS A POTENTIOMETER?
It is an electrical resistor with a variable resistance value and usually manually adjustable. The potentiometers have three terminals and are usually used in circuits of low current, for circuits of greater current the rheostats are used. In many electrical devices the potentiometers are what set the output level. For example, in loudspeaker, the potentiometer adjusts the volume, on a television or a computer monitor it can be used to control the brightness.
The value of a potentiometer is expressed in ohms as the resistors, and that value always corresponds to the maximum resistance it can have. The minimum vale is logically zero. For example, a 5kΩ potentiometer can have a variable resistor with values between 0Ω and 5000Ω.
The simplest potentiometer is a mechanically variable resistor. The first potentiometer simpler are the rheostats.
HOW DOES A POTENTIOMETER WORK?
A potentiometer consists of a mobile terminal that makes contact with a resistive element, as the mobile terminal moves, the resistance between the mobile terminal and the fixed ones of the device changes in proportion to the angular displacement. The change or variation of the resistance of a pot can be used to create an output voltage by means of the voltage division that is directly proportional to the input displacement.
HOW TO CONNECT A POTENTIOMETER?
The potentiometer has three terminals of which normally it is identified with the numbers 1,2 and 3 or A, B and C. Terminal A or 1 and B or 3 correspond to the terminals of connection to the circuit and terminal B or 2 is It can be interpreted as the signal connection or reference point. For better understanding, the potentiometer is represented as two resistors in series and the variable terminal (knob).
Normally the following configuration is used:
- Terminal A or 1: It corresponds to GND.
- Terminal B or 2: It corresponds to signal.
- Terminal C or 3: Corresponds to V or Input signal.
TYPES OF CONSTRUCTION OF A POTENTIOMETER
Printed potentiometer: Made with a cermet or carbon track on a hard support such as bakelised paper (cardboard prespan), fiberglass, bakelite, etc. The track has contacts at its ends and a cursor connected to a skate that slides down the resistive track.
Winding potentiometer: It consists of a toroidal winding of a resistive wire (could be constantan) with a cursor that moves a skate on itself.
TYPES OF POTENTIOMETERS
The potentiometers can be classified in two ways:
They are suitable for controlling the voltage in electronic devices. The user operates on them to vary the normal operating parameters of the electronic devices. For example, the volume of an audio device, vary the frequency of a radio.
- Rotary potentiometers: They are controlled by turning their axis. They are the most common because they are long lasting and use little space.
- Sliding potentiometers: The path of the cursor on the resistive track is straight, they are used in graphic equalizers. They are more fragile than rotary, they occupy more space and are usually more sensitive to dust.
- Multiple potentiometers: There are several potentiometers on a single axis, so they use little space. They use in instrumentation circuits, radios, etc.
According to the law of variation of resistance
- Linear variation : The resistance is directly proportional to the angle of rotation.
- Logarithmic: These are normally used for audio due to their asymmetric behavior due to the variation of their axis. At the beginning a very tenuous resistance increase is reflected, until reaching a point where the increase will be much greater, it is considered that the resistance depends logarithmically of the angle of rotation. They are often used for example for volume control of a radio.
- Senoidales: The resistance is proportional to the sine of the angle of rotation. Two integral sine-wave potentiometers rotated 90° provide the sine and cosine of the angle of rotation. They may have limit stops or not.
- Anti logarithmic
“There are also digital potentiometers (digital potentiometer is called an integrated circuit whose operation simulates that of an analog potentiometer). They have a resistive divider (voltage divider) with n+1 resistors”