Resistance ratings: designations, tables, resistor decoding possibilities

At the beginning of the 20th century, all resistances had very wide production tolerances, which was extremely inconvenient and caused many negative consequences. In this regard, it was necessary to look for ways to solve the problem, since electrical engineering developed by leaps and bounds. But only in 1952 the resistance values ​​were adopted. And this allowed a new look at the world of electronics, which gave a new impetus to its development.

General concept

Resistors act as a passive element in an electrical circuit, but are used in almost every one of them. Having constant or variable resistance, they convert voltage into current or vice versa, since, according to Ohm's law, these quantities are directly related to resistance.

Thus, the main parameter of resistors will be electrical resistance, which is usually measured in Ohms.

Designation on the diagrams

In the diagrams, these elements can be labeled differently, depending on the country and the nominal power dissipation. But the basis is based on the simplest forms shown in the figure.

And if everything is clear with the countries, then the power dissipation can raise questions. And this is nothing more than power that resistance can dissipate without harm to itself. Indeed, during the flow of electricity through the resistor, power is generated that heats it. If it is higher than the permissible value, then its overheating will follow, which will lead to the failure of the part.

In addition to the standard designation, some variations are possible to more accurately display the denomination. So, in a rectangle that schematically denotes resistance, there may be Roman numerals or stripes:

• Three slopes indicate a 0.05W resistor;
• Two inclined - 0.125 W;
• One oblique strip - 0.25 W;
• One horizontal strip - 0.5 W;
• Roman 1 - 1 W;
• Roman numeral 2 - 2 W;
• Roman 5 - 5 W.

Nominal range

Unnormalized tolerances in a wide field caused problems with the selection of resistances and their subsequent replacement. And all these inconveniences forced to resort to the formation of a nominal range, as a result of which nominal tolerances common for the production of resistors were established.

To understand the value of forming such a series, we can take as an example a 100 ohm resistance, which has a nominal deviation of 10%. For example, in a particular case, a 105 ohm resistor is required. But, given the ten percent deviation from one hundred ohms in both directions, it is easy to understand that this is resistance is suitable for the required 105 Ohm, and this eliminates the need to make a part for this values.

However, it would be more rational to make a 120 ohm resistor, since with a nominal deviation of 10%, it will cover values ​​from 108 to 132 ohms.

And this is much more convenient, because the same 100 and 105 ohms will be included in this interval. And besides them, many others will be able to enter here.

Denomination table

If you follow this logic, then with a nominal resistance deviation of 10% with a range from 100 to 1000 Ohms, they will be able to cover many values: 100, 120, 150 and so on, with standard rounding. Moreover, they all refer to the marking E12.

The relation to the EIA nominal series is shown here by the letter "E". And the number following it indicates how many logarithmic steps the range from 100 to 1000 will contain.

The following table of resistor ratings displays the values ​​of resistances 100-1000. When it is necessary to find out other ranges, it is easy to calculate them with the actions of division or multiplication.

There can be certain differences between the series:

• E6 - implies a tolerance of 20%;
• E12 - 10%;
• E24 - 5 and 2%;
• E48 - 2%;
• E96 - has a tolerance of 1%;
• E192 - indicates values ​​of 0.5%, 0.25%, 0.1% and above.

Color coding and code values

Most modern resistors, due to their too miniature dimensions, are often marked with color stripes. There can be 4, 5 and less often 6. Colors are applied to them far from beauty, and each of them has its own individual meaning, thanks to which you can easy to find out all the resistance data:

• The first two bars indicate the nominal resistance.
• If there are three or four bars, then the third indicates the multiplier.
• The fourth speaks of the accuracy of the resistance.

You can find out as accurately as possible which resistor is available using online calculators or thanks to a table of resistor colors.

If the designation is five-lane, then:

• The first three bars are the resistance value.
• The fourth is multiplier data.
• The fifth is an indication of accuracy.

Beginners are often interested in which side to count the stripes. For the first, it is customary to take the one that is closer to the edge. Golden stripes are not the first. This gives an additional opportunity to determine the origin with some resistors.

Alphanumeric coding can be used to indicate the value of the resistors. Four to five characters can convey all the information the user needs. The resistor value will be indicated here by the first characters. It can be multiple numbers and one letter. The letter indicates the position of the decimal point as well as the multiplier. The symbol at the end indicates a deviation.

SMD resistors

Due to their small size, SMD resistors are individually marked. It can be both numbers and numbers with letters. Designations meet in three variations:

1. Three digits - the first two digits will show the resistance value, and the last one is the multiplier.
2. Four digits - the three initial ones indicate the resistance of the resistor, and the fourth tells about the multiplier.
3. Two numbers and a symbol - the resistance indicator is hidden in the first two numbers, but you will need to use the table to decipher them. The symbol will denote a multiplier.

It is also necessary to take into account the letter that indicates the multiplier: S = 10¯²; R = 10¯¹; B = 10; C = 10²; D = 10³; E = 10⁴.

Determining the value of a resistor is not difficult if you know how to do it. Experienced electronics engineers keep a lot of information in their heads due to their extensive experience and regular contact with electrical parts.

As for amateurs and beginners, it is much easier for them to determine the denomination of parts using tables, which you can print and always keep close at hand, or online calculators to help you accurately determine the parameters details.