E-series and Resistor Color Codes

Preferred values in electronics¶

In electronics, often series of preferred values are used, which fully and optimally partition, combined with the tolerance, a decade of a certain physical quantity. These sets are based on a method developed by the Frenchman Charles Renard. For example, the distribution of the Euro currency is based on his R3 set.

E-series are used in electronics to provide capacitors, inductors, resistors, and zener diodes with their value. The E-series are indicated by En, where n is the amount of values per decade in the series. There are seven different series, where $n = 3, 6, 12, 24, 48, 96,$ and 192. If there are more values in the series, the tolerance can be reduced in size to still cover the complete range. The series can be roughly determined via $a(i,n)=F\cdot10^{i/n}$ , where $F = \ldots 10^{-1}, 10^{0}, 10^{1}, 10^{2} \ldots$ is the decade scaling factor, and $i=0,1,2 \ldots (n-1)$ . The above-mentioned series consist per decade the following typical values and tolerances.

Resistor Color Codes¶

The Resistor Color Code is a standardized marking system for axial-leaded components, including but not limited to resistors. It allows quick visual identification of their value and tolerance.

This system is essential in electronics because common resistors are too small for readable printed markings. Without it, identifying the value of mounted axial resistors and other axial components could be difficult or impossible.

Resistor values are indicated by colored bands around the body of the resistor, colors corresponding to the digits 0-9..
The bands are read sequentially to determine the value, typically starting with the band closest to the edge.
The resistance values indicated by the color code always correspond to one of the E-Series of Preferred Numbers (e.g., E12, E24, E96).
The total number of bands used depends on the number of significant digits required to accurately represent the specific E-series value.
The same code can also be used for axial components other than resistors.

The bands fall into three distinct functional categories:

Significant Digits: These are the first bands (two bands for E12/E24, three bands for E48/E96/E192) that specify the nominal resistance value’s numerical figures.
Multiplier: This is a single band that indicates the power of ten ( $10^x$ ) by which the significant digits must be multiplied to get the final resistance in Ohms ( $\Omega$ ).
Tolerance: This is the final band that specifies the allowable percentage deviation ( $\pm\%$ ) of the actual resistance from the nominal value, confirming its correspondence to a specific E-series.

See Figure 1 for an overview of resistor colour coding.

ripple — Figure 1:An overview of the resistance colour coding. (modified version of github.com/zeroping/reference-posters/)

For example:

a resistor of 1 $\Omega$ (5%) is noted in the E12 series as $10\cdot10^{-1}$ , which corresponds to colour code brown-black-gold-gold.
In the E96 series, 1 $\Omega$ (1%) is noted as $100\cdot10^{-2}$ , which corresponds to colour code brown-black-black-silver-brown.

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