In our daily life 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 that we wonder what a potentiometer is. It is basically a variable resistor, therefore, it serves to control the intensity that passes through a low-power electrical circuit, generally less than 1 W. In this way, we can say that the potentiometers allow setting the output level in many of the devices we commonly use.
As for the unit of measurement, the maximum resistance value is measured in ohms, so the symbol for the potentiometer 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 circuits with a lot of power, from 1 W.
Classification of potentiometers according to construction
To understand how a potentiometer works, you must first review its construction. In principle, we can mention the printed potentiometers, which have a cermet or carbon track on bakelite paper, fiberglass or other 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 serves to increase or decrease resistance.
On the other hand, there is a so-called wound potentiometer, which is composed 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 cursor 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 anyone 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 within electrical devices and are for strictly professional use, since they are usually very fragile.
The potentiometers for external use are the ones we use commonly. They are located on the surface of devices and are usually shaped like a rotary knob. As the non-specialist user has direct access to the external potentiometers, these tend to be more robust. An example of these are those that we find in an electric guitar.
The knob of the external potentiometers
Another important classification when talking about these devices is the form of 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. They are also often used frequently, therefore, they are very practical, resistant and durable.
As for the slide potentiometers, they 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 soft, but they can collect a lot of dust in the slots and take up more space than the rotary knobs.
Also, a few years ago multiple potentiometers were in fashion, which take up little space because several came with their coaxial shafts. They were used mainly in instrumentation and car radios.
What types of potentiometers are there?
To know the types of potentiometers that exist, it is necessary to take into account the law of the variation of resistance.
Among the most prominent is the linear potentiometer, which when activated produces a resistance proportional to the angle of rotation, in other words, if you move the rotary knob of the brightness of an old television, you will notice that the amount of light in the screen increases or decreases progressively. screen.
In contrast, a logarithmic potentiometer behaves asymmetrically. When you start turning the button, you can think that the resistance is proportional, but if you continue turning you will notice that each time the increase is much greater even if you move the button very little. This is what happens with the volume of a radio.
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 sinusoidal potentiometers fixed at 90 °. In this case, it is possible to find a potentiometer with or without a switch.
It is worth mentioning at this point the digital potentiometer, also called an electric potentiometer, which has an integrated circuit to mimic the operation of an analog one. The advantage of this is that it avoids the typical problems of mechanical devices. This type of device is 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.
However, to obtain maximum precision, a multiturn potentiometer is recommended, where the two fixed points at the ends are connected by means of a reduction screw, so the cursor must be moved through the entire spiral. In this case, to complete the entire route, you must turn the rotary knob more, so you can make the adjustment with greater precision.