RKM code explained

The RKM code, also referred to as "letter and numeral code for resistance and capacitance values and tolerances", "letter and digit code for resistance and capacitance values and tolerances", or informally as "R notation" is a notation to specify resistor and capacitor values defined since 1952 in the IEC 60062 (formerly IEC 62) standard of the International Electrotechnical Commission. Corresponding national standards include DIN 40825 (1973) of the Deutsches Institut für Normung, BS 1852 (1975) of British Standards Institution, and IS 8186 (1976) of the Bureau of Indian Standards; as well as the pan-European EN 60062 (1993) of the European Standards Organizations. The updated IEC 60062:2016, amended in 2019, comprises the most recent release of the standard.

Overview

Originally meant also as part marking code, this shorthand notation is widely used in electrical engineering to denote the values of resistors and capacitors in circuit diagrams and in the production of electronic circuits (for example in bills of material and in silk screens). This method avoids overlooking the decimal separator, which may not be rendered reliably on components or when duplicating documents.

The standards also define a color code for fixed resistors.

Part value code

Examples of resistance values
R47
4R7
470R
4K7
47K
47K3
470K
4M7
For brevity, the notation often does not specify the unit (ohm or farad) explicitly and instead relies on implicit knowledge raised from the usage of specific letters either only for resistors or for capacitors, the case used (uppercase letters are typically used for resistors, lowercase letters for capacitors), a part's appearance, and the context.

The notation also avoids using a decimal separator and replaces it by a letter associated with the prefix symbol for the particular value.

This is not only for brevity (for example when printed on the part or PCB), but also to circumvent the problem that decimal separators tend to "disappear" when photocopying printed circuit diagrams.

Another advantage is the easier sortability of values which helps to optimize the bill of materials by combining similar part values to improve maintainability and reduce costs.

The code letters are loosely related to the corresponding SI prefix, but there are several exceptions, where the capitalization differs or alternative letters are used.

For example, 8K2 indicates a resistor value of 8.2 kΩ. Additional zeros imply tighter tolerance, for example 15M0.

When the value can be expressed without the need for a prefix, an R or F is used instead of the decimal separator. For example, 1R2 indicates, and 18R indicates .

Notes and References

  1. Book: ISO 2955-1974: lnformation processing - Representations of SI and other units for use in systems with limited character sets . 1 . 1974.
  2. Book: ISO 2955-1983: lnformation processing - Representations of SI and other units for use in systems with limited character sets . Table 2 . 1983-05-15 . 2 . 2016-12-14. https://web.archive.org/web/20161214025341/http://www.bgu.ac.il/~averbukh/ISO_2955-1983E.pdf -->
  3. Book: Vornorm DIN 66030 . de . Preliminary standard DIN 66030 . January 1973.
  4. Book: DIN 66030: Informationsverarbeitung - Darstellungen von Einheitennamen in Systemen mit beschränktem Schriftzeichenvorrat . de . Information processing; representations for names of units to be used in systems with limited graphic character sets . . 1 . November 1980 . 2016-12-14.
  5. Neue Normen für die Informationsverarbeitung . de . . 1981-01-09 . 2016-12-14 . live . https://web.archive.org/web/20161214025700/http://www.computerwoche.de/a/neue-normen-fuer-die-informationsverarbeitung%2C1184901 . 2016-12-14.
  6. Book: DIN 66030:2002-05 - Informationstechnik - Darstellung von Einheitennamen in Systemen mit beschränktem Schriftzeichenvorrat . de . Information technology - Representation of SI and other units in systems with limited character sets . May 2002 . . 2016-12-14.
  7. Book: ГОСТ IEC 60062-2014 . 2014 . ru . GOST (ГОСТ) . 2022-06-16 . live . https://web.archive.org/web/20220210082045/http://gostexpert.ru/data/files/60062-2014/68492.pdf . 2022-02-10.
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  9. Book: BS 1852:1975 .
  10. Book: BS EN 60062:1994 .
  11. Book: BS EN 60062:2005 .
  12. Book: BS EN 60062:2016 .
  13. IEC 60062:1974
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