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Encyclopedia > Preferred values
The E12 values follow a geometric series

In electronics, certain types of passive components such as resistors, capacitors and inductors are manufactured with a standardised range of values called preferred values. Image File history File links Download high resolution version (1258x770, 29 KB) Summary This is a graph of E12 resistor values, from 1 to 82. ... Image File history File links Download high resolution version (1258x770, 29 KB) Summary This is a graph of E12 resistor values, from 1 to 82. ... Two digital voltmeters The field of electronics is the study and use of electronic devices that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors. ... Resistor symbols A resistor is a two-terminal electrical or electronic component that passes a current that is proportional to the potential difference between its terminals in accordance with Ohms law. ... Various types of capacitors A high voltage (15 kV AC) capacitor A capacitor is a device that stores energy in the electric field created between a pair of conductors on which equal but opposite electric charges have been placed. ... // Definition An inductor is a passive electrical device that stores energy in a magnetic field, typically by combining the effects of many loops of electric current. ...

For example, in the so-called E12 range, there are twelve values in each decade. These are:

` 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2 `

This means that E12 resistors exist with values of 3.3 ohms, 33 ohms, 330 ohms, 3300 ohms etc. but not with values such as 2 ohms or 8.3 ohms.

The E12 series is an approximation of a geometric series, with the ratio between adjacent values being or about 1.212. The reason for the choice of twelve values is based on the tolerance of 10% with which some resistors are made. This tolerance means that a resistor marked "27 ohms 10%" could be as low as 24.3 ohms or as high as 29.7 ohms. Therefore there would be no point in selling resistors whose values were closer together than E12, since the tolerance would be greater than the spacing between values. In mathematics, a geometric progression is a sequence of numbers such that the quotient of any two successive members of the sequence is a constant called the common ratio of the sequence. ... Tolerance is a social, cultural and religious term applied to the collective and individual practice of not persecuting those who may believe, behave or act in ways of which one may not approve. ...

For 2% and 5% tolerance components, the E24 series is used. This contains the following values:

` 1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9, 4.2, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1 `

For 1% tolerance components, the E96 series is used:

` 100, 102, 105, 107, 110, 113, 115, 118, 121, 124, 127, 130, 133, 137, 140, 143, 147, 150, 154, 158, 162, 165, 169, 174, 178, 182, 187, 191, 196, 200, 205, 210, 215, 221, 226, 232, 237, 243, 249, 255, 261, 267, 274, 280, 287, 294, 301, 309, 316, 324, 332, 340, 348, 357, 365, 374, 383, 392, 402, 412, 422, 432, 442, 453, 464, 475, 487, 499, 511, 523, 536, 549, 562, 576, 590, 604, 619, 634, 649, 665, 681, 698, 715, 732, 750, 768, 787, 806, 825, 845, 866, 887, 909, 931, 953, 976 `

For the 0.5% the E192 series is used; this series is too long to list here!

For components with very wide tolerances such as large-valued capacitors, the E6 series is used, as follows:

1.0, 1.5, 2.2, 3.3, 4.7, 6.8

The series of preferred values are specified in IEC (International Electrotechnical Commission) publication 60063 (1963-01). The International Electrotechnical Commission (IEC) is an international standards organization dealing with electrical, electronic and related technologies. ...

The series of values for the current ratings of fuses does not adhere to the IEC standards, but uses ten equal intervals per decade. After some arbitrary rounding, this results in the series: 200 A Industrial fuse. ...

` 1, 1.25, 1.6, 2, 2.5, 3.15, 4, 5, 6.3, 8 `

This external page may be used to explore colour codes and E-ranges: http://www.okaphone.nl/calc/resistor.shtml Electronic color codes are used to indicate the values or ratings of electronic components, near-universally for resistors, but also for capacitors, inductors, and others. ...

Results from FactBites:

 Preferred number - Wikipedia, the free encyclopedia (1504 words) Preferred numbers are chosen such that when a product is manufactured in many different sizes, these will end up roughly equally spaced on a logarithmic scale. In some applications more rounded values are desirable, either because the numbers from the normal series would imply an unrealistically high accuracy, or because an integer value is needed (e.g., the number of teeth in a gear). For larger dimensions, preference is given to multiples of the modules 12 M (= 1.2 m), 15 M (= 1.5 m), 30 M (= 3 m), and 60 M (= 6 m).
 Preferred values - definition of Preferred values in Encyclopedia (351 words) The reason for the choice of twelve values is based on the tolerance of 10% with which some resistors are made. The series of preferred values are specified in IEC (International Electrotechnical Commission) publication 60063 (1963-01). The series of values for the current ratings of fuses does not adhere to the IEC standards, but uses ten equal intervals per decade.
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