How a potentiometer works

In our daily lives we use potentiometers frequently, since they allow us to control the functions of some devices, such as raising and lowering the volume on a music player, sound amplifier or electric guitar. However, many of us do not really know how this device works.

It is normal for us to wonder what a potentiometer is. It is basically a variable resistor, therefore, it is used to control the intensity that passes through a low-power electrical circuit, generally less than 1 W. In this way, we can say that potentiometers allow the output level to be set in many of the devices we commonly use.

As for the unit of measurement, the maximum resistance value is measured in ohms, so the potentiometer symbol is the Greek omega Ω, as is the case with other types of electrical resistors. Thus, a 50 KΩ potentiometer offers a variable resistance from 0 Ω to 50,000 Ω. The most common are 10, 100, 250 and 500 KΩ, but there are other options. However, potentiometers should not be confused with rheostats, since the latter are indicated for high power circuits, starting at 1 W.

Classification of potentiometers according to construction

To understand how a potentiometer works, you must first review how it is built. In principle, we can mention the printed potentiometers, which have a cermet or carbon track on bakelized paper, fiberglass or another hard material that serves as a support. In this sense, the potentiometer connection has a track with two fixed terminals, one at each end, as well as a variable terminal that is used to increase or decrease the resistance. 

On the other hand, there is the so-called wirewound potentiometer, which is made up of a toroidal support with a resistive wire that makes turns on it and lets the energy flow. To regulate the resistance, it incorporates a slider that makes a skate move. We must mention at this point that to achieve the resistance law in a printed potentiometer, the width of the resistive track must be varied, while in a wound one, the curve is adjusted in sections, with wires of different diameters.

Internal and external potentiometers

We agree that potentiometers are not items that everyone has in their toolbox (here are some purchase options), in fact, most of us probably would not know how to connect a potentiometer, since it is usually a appliance used by trained technical personnel. This is why we must make a distinction between internal potentiometers, which, as their name indicates, are found inside electrical devices and are for strictly professional use, since they are usually very fragile.

External use potentiometers are the ones we commonly use. They are found on the surface of devices and are usually shaped like a rotary knob. As the non-specialized user has direct access to external potentiometers, these are usually more resistant. An example of these are those found in an electric guitar.

The control of the external potentiometers

Another important classification when talking about these devices is the shape of the control. In this case we refer to the external potentiometers that we commonly use in devices. One of the most popular is the rotary potentiometer, which is very practical because you only have to turn its axis by pressing the button with your fingers. In addition, they are often used frequently, therefore, they are very practical, resistant and durable.

As for the slider potentiometers, these have a linear resistive track, so to lower or raise the resistance you have to move the cursor in a straight line. They are common in amplifiers and graphic equalizers, but old radio players also had these types of potentiometers. They are very comfortable and smooth, but they can collect a lot of dust in the slots and take up more space than rotary knobs.

Also, a few years ago multiple potentiometers were fashionable, which take up little space because several came with their coaxial axes. They were used mainly in instrumentation and car radios.

What types of potentiometers are there?

To know the types of potentiometers that exist, the law of resistance variation must be taken into account.

linear potentiometer

Among the most prominent is the linear potentiometer, which when actuated produces a resistance proportional to the angle of rotation, in other words, if you move the brightness rotary knob on an old television, you will notice that the amount of light in the screen progressively increases or decreases. screen.

logarithmic potentiometer

In contrast, a logarithmic potentiometer behaves asymmetrically. As you start to turn the knob you might think that the resistance is proportional, but if you continue to turn you will notice that the increase is much larger each time even if you move the knob very little. This is what happens with the volume of a radio.

Sine potentiometer

There is also the potentiometer called sinusoidal. It receives this name because the resistance varies according to the sine of the angle. In this way, the sine and cosine of the angle of rotation are obtained with two solidary sinusoidal potentiometers at 90°. In this case, it is possible to find a potentiometer with or without a switch.

digital potentiometer

It is worth mentioning at this point the digital potentiometer, also called an electrical potentiometer, which has an integrated circuit to imitate the operation of an analog one. The advantage of this is that it avoids the typical problems of mechanical devices. These types of devices are made up of a resistive divider that has n+1 resistors. It is good to know that the most used today are the 10k potentiometer and the 100k potentiometer.

multiturn potentiometer

However, to obtain maximum precision, a multi-turn potentiometer is recommended, where the two fixed points at the ends are connected by a reduction screw, so the cursor must move through the entire spiral. In this case, to complete the entire route you must turn the rotary button more times, so you can make the adjustment more accurately.

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