Components and wires are coded with colors to identify their value and function. Resistor Color Coding uses colored bands to quickly identify a resistors resistive value and its percentage of tolerance with the physical size of the resistor indicating its wattage rating.
Generally, the resistance value, tolerance, and wattage rating are printed on the body of a resistor as numbers or letters when the resistors body is big enough to read the print, such as large power resistors. But when a resistor is smaller (example: 1/4 watt carbon or film type), the print is too small to read, so the specifications must be shown in another way.
The colors brown, red, green, blue, and violet are used as tolerance codes on 5-band resistors only. All 5-band resistors use a colored tolerance band. The blank (20%) “band” is only used with the “4-band” code (3 colored bands + a blank “band”).
A resistor colored Yellow-Violet-Orange-Gold would be 47 kΩ with a tolerance of +/- 5%.
A resistor colored Green-Red-Gold-Silver would be 5.2 Ω with a tolerance of +/- 10%.
A resistor colored White-Violet-Black would be 97 Ω with a tolerance of +/- 20%. When you see only three color bands on a resistor, you know that it is actually a 4-band code with a blank (20%) tolerance band.
A resistor colored Orange-Orange-Black-Brown-Violet would be 3.3 kΩ with a tolerance of +/- 0.1%.
A resistor colored Brown-Green-Grey-Silver-Red would be 1.58 Ω with a tolerance of +/- 2%.
A resistor colored Blue-Brown-Green-Silver-Blue would be 6.15 Ω with a tolerance of +/- 0.25%.
To make mass manufacturing of resistors easier, the IEC (International Electrotechnical Commision) defined tolerance and resistance values for resistors in 1952. These are referred to as preferred values or E-series, published in standard IEC 60063:1963. Capactors, Zener diodes, and inductors also use these standards.
The purpose of this was so that when companies produce resistors with different values of resistance, they would equally space on a logarithmic scale.
This helps the supplier with stocking different values. Resistors produced by different manufacturers are compatible for the same designs because of the use of standard values.
The standard E3, E6, E12, E24, E48 and E96 resistor values are listed below.
# of Values
in Each Decade
|E192||0.5%, 0.25% and higher tolerances|
*The calculated tolerance for this series is 36.60%, While the standard only specifies a tolerance greater than 20%, other sources indicate 40% or 50%.
These are the most widely used resistor series in the electronics industry and are useful for resistor values that are not critical. The number of different components in any electronic circuit design can be reduced by keeping to this series.
The E6 series of resistors are also widely used in the electronics industry because of their wider range of common resistor values.
Though, resistors in ranges up to E24 are available, it helps in any design to focus on using as small a number of resistor values as possible. This will reduce the number of components in a design and this will help reduce costs when considering large-scale production.
The E96 and E192 series of standard resistor values do exist, but they are not used as much as the Series mention previously. Their tolerance is either 0.5 or 0.25% which can increase costs along with a much higher number of resistors in range.
by Robert Keim
by Gary Elinoff