A potentiometer is a voltage divider, i.e. a resistor with 3 terminals, one of which is movable. Potentiometers are passive components, where the ratio between the resistances at both ends can be changed by moving a slider or pushing a button. The potentiometer consists of a resistor, a sliding contact, electrodes, an actuator and housing.
Potentiometers are used to control electric and electronic devices with low power up to 1W. If greater loads need to be managed according to the same principle, rheostats are used. In this sense, the potentiometer can be seen as a modification of the rheostat. The power that can be controlled by the potentiometer is displayed on its housing, and is an important parameter, together with its resistance. If there is an attempt to exceed the power, the potentiometer begins to emit considerable heat, which can lead to its destruction.
A potentiometer, as a voltage divider, can be represented as a device of two successive sections of the electrical circuit, called arms. The sum of their voltages is equal to the input voltage. The arm between the neutral potential and the midpoint is called low and the other one – high. The resistance can be active or reactive. The simplest voltage divider represents two resistors R1 and R2 connected in series to a voltage source.
Since resistances are connected in series according to Kirchhoff’s first law, the current passing through them will be the same, and the voltage drop will be calculated by Ohm’s law and it will be proportional to the resistance:
U1 = IR1;
U2 = IR2.
Dividing the voltages we receive:
U1/U2 = R1/R2
and thus the ratio between the voltages is exactly equal to the ratio between the resistances and U1 + U2 = U, as well as R = R1 + R2.
A potentiometric sensor (converter) can be created through the principle of the potentiometer. It is a sensor whose input signal is displacement of the contact terminal and the output one – voltage that can be taken down from the two poles of the potentiometer. There are two main types of potentiometric transducers:
A potentiometric angular position transducer;
a potentiometric linear position transducer.
There is a huge variety of potentiometers, depending on their structure, application and the resistive element that is used.
According to the shape of the housing and the movement of the slider (the movable contact) there are:
- rotary or axial
According to the used resistive material:
- carbon or graphite (mono and stereo-carbon).
According to the principle of installation:
- surround mounting;
- PCB mounting.
According to the number of turnovers that the rotary potentiometer can make:
According to the law of change of the resistance:
According to the need for adjustment during operation:
- trimmer potentiometers.
Of course, combinations between the different potentiometers are also possible, except the obviously impossible ones. After selecting the right potentiometer to regulate the given process, in most cases – adjusting the volume of audio equipment, we need to proceed with selecting the suitable button.
The choice is really big and you can choose between buttons with flanges, rings, light indication, cylindrical, conical, with indicator lines of different colors, with benchmarks. There are metal, aluminum, plastic buttons, buttons for rotary and slide potentiometers.
With the development of electronic technologies, besides conventional potentiometers, the so called digital potentiometers appeared on the market. These potentiometers have no moving parts and are integrated circuits that can be programmed to change their own resistance according to a predetermined step.