Resistors are elements of electrical circuits that resist the passage of electric current. They are used in all electrical circuits, even the most elementary ones. Resistors are distinguished according to the following criteria: by power, by the value of the nominal resistance, by accuracy class, by type, etc. In this article, we will consider such a thing as the value of a resistor. What it is? The nominal value of a resistance element means the value of the level of internal resistance to the passage of electric current through it. In electrical engineering, the resistor value is indicated by the Latin letter R. This value is usually written in units of measurement such as ohms. This unit got its name in honor of the famous German physicist Georg Simon Ohm, known for his work in the field of studying electric current. Why do you need to know the value of the resistors? To choose the right elements for the designed circuit or to choose an analogue when repairing devices.
Let's consider ways of writing the nominal values of resistance on the body of the elements. There are three ways to label resistors:digital - includes only numbers; symbolic - is combined, along with numbers there are also letters; and, finally, color - is a series of transverse stripes of different colors, the number of stripes varies, from 3 to 5.
Next, we will analyze how the value of the resistor is written depending on the type of element. Wire-type constant resistance elements are a cylindrical barrel. Such elements are marked in all three ways. Digital recording is used only for resistors whose nominal value does not exceed 999 ohms. It looks like this: 2, 0; 220; 750. Means, respectively: 2 ohms, 220 ohms and 750 ohms. The following type of record uses letters of the Latin alphabet instead of a comma: R - means one; K - kilo, that is, 1000; M - mega, that is, 1000000. It turns out that with this recording method, in order to get the value of the resistor, it is necessary to multiply the digital value by the letter value. An example of such an entry: 220 R - means 220 ohms; 3K2 - means 3200 Ohm; 1M1 - means 1100 kOhm.
The color coding of the nominal value record is applied across the cylindrical body of the element. In Soviet-made resistors, the marking was applied with an offset to one of the sides, this indicated the start of the decoding countdown. In modern elements, the last stripe of the barcode is always gold or silver, and it means the resistance accuracy class (5 or 10 percent). In the event that the marking consists of only three stripes, the default accuracy class20 percent is assumed. The encoding, consisting of 3-4 bands, in the first two contains the value of the face value, and the third - the value of the multiplier. An encoding of 5-6 bands in the first three contains the value of the face value, and in the fourth - the value of the multiplier.
The next kind of resistance is chip resistor or SMD resistor. In such resistors, the marking is digital and symbolic. It is deciphered simply: in digital marking, the first digits indicate the value of the face value, and the last one indicates the number of zeros; in symbolic - the first two digits indicate the face value, and the last character - the value of the multiplier.
In variable resistors, the standard notation of the nominal value is used using numbers and letters of the Latin alphabet.
