A resistor is one of the main elements of an electric circuit, which has constant or variable resistance and serves to convert electric current to voltage (and vice versa), absorb electricity and to perform a number of other operations.
This passive element is an integral part of any device. Therefore, if you consider yourself an experienced electrician or just a lover of radio electronics, you will also need the
marking of resistors with colored strips and alphanumeric characters to compare the characteristics of different components.
Designation of resistors in the diagrams
On the schematic diagrams of electrical devices, the resistor is indicated in the form of a rectangle, on top of which is placed the letter of the Latin alphabet R. Following the symbol is a serial number by which the element can be found in the specification. The circuit designation is completed by a set of numbers that indicate the nominal resistance. So, the inscription R12 100 will mean that 12 resistors with a resistance of 100 ohms are installed.
An important characteristic of elements is their power. If you ignore this parameter, you run the risk of disabling the entire circuit, even if the resistor labeling was done correctly. In the diagrams it is indicated:
- Roman numerals ranging from 1 to 5 watts;
- horizontal strip at a value of 0.5 watts;
- one or two inclined lines at a power of 0.25 and 0.125 watts, respectively.
After the serial number of some resistors, there may be a "*" sign. It means that the characteristics given are only approximate. You will need to choose the exact values yourself.
Alphanumeric designation
Alphanumeric marking is characteristic of Soviet-made elements, as well as some world-class products.
The marking of imported resistors and domestic products can begin with either a digit or a symbol. In this case, the units are indicated as follows:
- the symbol "E" or "R" indicates that the denomination is expressed in ohms;
- the letter "M" tells us that resistance is expressed in megaohms;
- the “K” sign complements all numerical values expressed in kilo-ohms.
If the character is after the numbers, then all values are expressed in whole units (33E = 33 Ohms). To indicate the fraction, the letter is placed before the numbers (K55 = 0.55 kilo-ohms = 550 Ohms). If the sign separates the numbers, then the resistivity is expressed in integer values with a fractional part (1M3 = 1.3 megaohm).
Denomination in color
The length of some “resistances” is only a few millimeters. It is impossible to apply and consider letters and numbers on such an element. To compare such components, resistor markings are used with colored strips. The first two bands are always responsible for the face value. Other stripes have a certain meaning:
- in 3- or 4-way markings, the third dash defines the factor, and the fourth dashes the accuracy;
- in 5-band designations, the third color indicates the face value, the fourth indicates the factor, and the fifth indicates accuracy;
- the sixth strip indicates the temperature coefficient of resistance or the reliability of the element, if it is thicker than the rest.
The color of the bars indicates the numerical values assigned to them. To deal with this, the resistor labeling table will help, where each shade corresponds to a certain factor, or figure.
For example, we have a resistor with red, green, brown, and blue stripes. Having deciphered the values, we find out that we have a resistor with a resistance of 25 * 10
Ohms = 250 Ohms with an accuracy of 25%.
Strip sequence
How to determine which side to start decryption? After all, the labeling of resistors with color strips can be decrypted in both directions.
In order not to get confused in this, you should remember a few simple rules:
- If there are only three bands, the first will always be closer to the edge than the last.
- In 4-way elements, the reading direction should be determined by the silver or gold color - they will always be closer to the end.
- In other cases, it is necessary to read so that a value is obtained from the nominal series. If it doesn’t work, it’s worth decrypting it from the other side.
A separate case is the location of one black jumper on the case. It means that the element has no resistance and is used as a jumper. Now you know how the marking of resistors is read in colored strips, and you will not have problems with determining the value of the element.