Resistor values are organized into a set of different series of preferred values or standard resistor values.
These standard resistor values have a logarithmically based sequence and this permits the various values to be spaced in such how that they relate to the component tolerance or accuracy.
Resistor tolerances are generally ±20%, ±10% ±5%, ±2%, and ±1%. More accurate tolerances are available for some resistors, but these are not as widely available and costs are higher.
By having these standard resistor values, electronic components from a variety of manufacturers can be chosen, making sourcing much easier and the cost of the components much less. This series is also used for a variety of other electronic components.
E series of Standard Resistor Values
The standard resistor values are organized into a group of series of values referred to as the E-series. The different values are spaced such that the top of the tolerance band of one value and the bottom of the tolerance band of the next one do not overlap.
The different sets of standard resistor values are known by their E-series numbers: E3 has three resistors in each decade, E6 has six, E12 has twelve, and so forth.
The most basic series within the E range is that the E3 series which has just three values: 1, 2.2, and 4.7. This is seldom used as such because the associated tolerance is too wide for most of today’s applications, although the basic values themselves may be used more widely to reduce stock holding.
The next is the E6 series with six values in each decade for a ±20% tolerance, E12 series with 12 values in each decade for a ±10%, E24 series with 24 values in each decade for a ±5% tolerance. Values for resistors in these series are given below. Further series (E48 and E96) are available but are not as common as the ones given below.
The E6 and E12 resistors are available in virtually all kinds of the resistor. However, the E24 series, being a much closer tolerance series is only available in the higher tolerance types. Metal oxide film resistors that are in common use today are available within the E24 series as are several other types. Carbon types are rarely available these days and in any case, would only available in the lower tolerance ranges as their values cannot be guaranteed to such a close tolerance.
The E series preferred or standard resistor value ranges are internationally accepted and have been adopted by international standards organizations. The EIA (Electrical Industries Association) which is based in North America is one organization that has adopted the system and as a result, the resistor value series is often referred to as the EIA standard resistor values.
E SERIES TOLERANCE
(SIG FIGS) NUMBER OF VALUES IN EACH DECADE
E3 >20% 3
E6 20% 6
E12 10% 12
[normally also available in 2% tolerance] 24
E48 2% 48
E96 1% 96
E192 0.5%, 0.25% and higher tolerances 192
Note: The metal film resistors now widely used for axial resistors and therefore the surface mount resistors are normally available in 1% and a couple of tolerance ratings even when included within the E24, E12, E6, and E3 ranges.
The E series values are split into two groups which have slightly different numbering, although they follow the same basic numerology:
Up to E24: For this lower end of the E series used for resistors, capacitors, and other component values, the main difference is that the numbers have only two significant figures as this is all that is really needed.
E48 to E192: For the E48 to E192 series there significant figures are used for all the values as it is necessary to define them more accurately in view of the higher number of values needed.
It can be seen that some of the values in the E24 series do not exist in E48 to E192 series. This arises dues to the different rounding rules used.
Resistor E series
The EIA preferred values or standard resistor values can be summarised in a tabular form to give the different values within each decade.
Current resistor technology enables very close tolerance levels to be achieved, yet there is still a great benefit in using resistors even from the E3 series. It reduces the number of different types of resistors used in a design and this simplifies purchasing and manufacturing processes. Often designs try to keep to the E3 or E6 standard resistor values, only using those in the E12, E24, E48, or E96 if absolutely necessary.
One example where values can be kept within the E3 series occurs with digital design where a pull-up or pull-down resistor is needed. The exact value is of little consequence – only value within the approximate region is needed. For these resistors, the value can be selected within the E3 series.
Resistor E series tables of values
Below are the common resistor values. They are the quality E3, E6, E12, E24, E48, and E96 resistor values.
The E3 series resistors are the foremost widely used and hence these values are going to be the foremost common resistor values used within the industry. They are particularly useful for resistor values that are not in any way critical. By keeping to this series, the number of different components in any electronic circuit design can be reduced and this can help reduce manufacturing costs by reducing inventory and the additional management and set up required for additional component types in design.
|E6 STANDARD RESISTOR SERIES|
The E6 series resistor values are also widely used within the industry. They provide a wider range of common resistor values that can be used.
|E12 STANDARD RESISTOR SERIES|
|E24 STANDARD RESISTOR SERIES|
|E48 STANDARD RESISTOR SERIES|
|E96 STANDARD RESISTOR SERIES|