Resistor

About D.E.V.I.C.E.

A resistor is an electrical component that implements electrical resistance.

Standard Resistor Values

Resistor values are organised into a set of different series of preferred values or standard resistor values.

These standard resistor values have a logarithmically based sequence and this enables the different values to be spaced in such a way 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.

E series of standard resistor values

The standard resistor values are organized into a set of series of values known 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.

Take as an example a resistor that has a value of 1 Ohm and a tolerance of ±20%. The actual resistance at the top of the tolerance band is 1.2 Ohms. Take then a resistor with a value of 1.5 Ohms. The resistance of this component at the bottom of its tolerance band is 1.2 Ohms. This process is followed through for all the values in a decade, creating a set of standard resistor values for each tolerance.

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 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 types of resistor. However the E24 series, being a much closer tolerance series is only available in the higher tolerance types.

Summary of EIA preferred or standard resistor value series

E series Tolerance (SIG FIGS) Number of values in each decade
E3 >20% 3
E6 20% 6
E12 10% 12
E24 5% (normally also available in 2% tolerance) 24
E48 2% 48
E96 1% 96
E192 0.5%, 0.25% and higher tolerances 192

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