Letter and digit code

The letter and digit code for resistance and capacitance values and tolerances, which is also known as RKM code or "R notation", is a notation to specify resistor and capacitor values defined in the international standard IEC 60062 (formerly IEC 62) since 1952. It is also adopted by various other standards including DIN 40825 (1973), BS 1852 (1974), IS 8186 (1976) and EN 60062 (1993). The significantly updated IEC 60062:2016 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

For brevity, the notation omits to always 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,[nb 1] the case used (uppercase letters are typically used for resistors, lowercase letters for capacitors),[nb 2] 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.

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" is used instead of the decimal separator. For example, 1R2 indicates 1.2 Ω, and 18R indicates 18 Ω.

Examples of resistance values
R47 0.47 ohm
4R7 4.7 ohm
470R 470 ohm
4K7 4.7 kiloohm
47K 47 kiloohm
47K3 47.3 kiloohm
470K 470 kiloohm
4M7 4.7 megaohm
Code letter Prefix Multiplier
Resistance [Ω] Capacitance [F] Name Symbol (SI) Base 10 Base 1000 Value
- p (P[nb 2]) pico- p ×10−12 ×1000−4 ×0.000000000001
- n (N[nb 2]) nano- n ×10−9 ×1000−3 ×0.000000001
- µ (u, U[nb 2]) micro- µ ×10−6 ×1000−2 ×0.000001
L m (M[nb 1][nb 2]) milli- m ×10−3 ×1000−1 ×0.001
R (E[nb 3]) F - - ×100 ×10000 ×1
K (k[nb 4]) - kilo- k ×103 ×10001 ×1000
M[nb 1] - mega- M ×106 ×10002 ×1000000
G - giga- G ×109 ×10003 ×1000000000
T - tera- T ×1012 ×10004 ×1000000000000

For resistances, the standard dictates the use of the uppercase letters L (for 10−3), R (for 100 = 1), K (for 103), M (for 106), and G (for 109) to be used instead of the decimal point.

The usage of the letter R instead of the SI unit symbol Ω for ohms stems from the fact that the Greek letter Ω wasn't (and still isn't) part of most character sets and therefore is sometimes impossible to reproduce, in particular in some CAD/CAM environments. The letter R was chosen because visually it loosely resembles the Ω glyph, and also because it works nicely as a mnemonic for resistance in many languages.

The letters G and T weren't part of the first issue of the standard, which pre-dates the introduction of the SI system (hence the name "RKM code"), but were added after the adoption of the corresponding SI prefixes.

The introduction of the letter L in more recent issues of the standard (instead of an SI prefix m for milli) is justified to maintain the rule of only using uppercase letters for resistances (the otherwise resulting M was already in use for mega).

Similar, the standard prescribes the following lowercase letters for capacitances to be used instead of the decimal point: p (for 10−12), n (for 10−9), µ (for 10−6), m (for 10−3), but uppercase F (for 100 = 1) for farad.

The letters p and n weren't part of the first issue of the standard, but were added after the adoption of the corresponding SI prefixes.

In cases, where the Greek letter µ is not available, the standard allows it to be replaced by u (or U, when only uppercase letters are available). This usage of u instead of µ is also in line with ISO 2955 (1974,[1] 1983[2]), DIN 66030 (Vornorm 1973;[3] 1980,[4][5] 2002[6]) and BS 6430 (1983), which allow the prefix μ to be substituted by the letter u (or U) in circumstances, in which only the Latin alphabet is available.

Tolerance code

Letter code for resistance and capacitance tolerances:

Code letter Tolerance
Resistance Capacitance Relative Absolute
Symmetrical Asymmetrical C <10 pF only
A A variable (±0.05%) variable variable
B B ±0.1% N/A
C C ±0.25% N/A ±0.25 pF
D D ±0.5% N/A ±0.5 pF
E ±0.005% N/A N/A
F F ±1.0% N/A ±1.0 pF
G G ±2.0% N/A ±2.0 pF
H H ±3.0% N/A N/A
J ±5.0% N/A N/A
K ±10% N/A N/A
L ±0.01% N/A N/A
M ±20% N/A N/A
N ±30% N/A N/A
P ±0.02% N/A N/A
Q N/A −10/+30% N/A
S N/A −20/+50% N/A
T N/A −10/+50% N/A
W ±0.05% N/A N/A
Z N/A −20/+80% N/A

Production date code

Example: V8 = August 2007 (or August 1987)

Corresponding standards

See also

Notes

  1. 1 2 3 The letter M was an exception to the rule that all different letters are supposed to be used for resistances and capacitances. Today, a lowercase letter m should be used for capacitances whenever possible to avoid confusion.
  2. 1 2 3 4 5 In old issues of the IEC 60062 standard, uppercase Latin letters were not only used for resistances, but also for capacitance values, whereas newer issues specifically use lowercase letters for capacitors (except for the special case of F).
  3. ↑ The usage of the Latin letter E instead of R is not standardized in IEC 60062, but nevertheless sometimes seen in practice. It stems from the fact, that R is used in symbolic names for resistors as well, and it is also used in a similar fashion but with incompatible meaning in other part marking codes. It may therefore cause confusion in some contexts. Visually, the letter E loosely resembles a small Greek letter omega (ω) turned sideways. Historically (f.e. in pre-WWII documents), before ohms were denoted using the uppercase Greek omega (Ω), a small omega (ω) was sometimes used for this purpose as well, as in 56ω for 56 Ω. However, the letter E is conflictive with the similar looking but incompatible E notation in engineering, and it may therefore cause considerable confusion as well.
  4. ↑ The IEC 60062 standard prescribes the usage of an uppercase Latin letter K only, however, a lowercase k is often seen in schematics and bills of materials probably because the corresponding SI prefix is defined as a lowercase k.

References

  1. ↑ ISO 2955-1974: lnformation processing - Representations of SI and other units for use in systems with limited character sets (1st ed.). 1974.
  2. ↑ "Table 2". ISO 2955-1983: lnformation processing - Representations of SI and other units for use in systems with limited character sets (PDF) (2nd ed.). 1983-05-15. Retrieved 2016-12-14.
  3. ↑ Vornorm DIN 66030 [Preliminary standard DIN 66030] (in German). January 1973.
  4. ↑ DIN 66030: Informationsverarbeitung - Darstellungen von Einheitennamen in Systemen mit beschränktem Schriftzeichenvorrat [Information processing; representations for names of units to be used in systems with limited graphic character sets] (in German) (1st ed.). Beuth Verlag. November 1980. Retrieved 2016-12-14.
  5. ↑ "Neue Normen für die Informationsverarbeitung". Computerwoche (in German). 1981-01-09. Archived from the original on 2016-12-14. Retrieved 2016-12-14.
  6. ↑ DIN 66030:2002-05 - Informationstechnik - Darstellung von Einheitennamen in Systemen mit beschränktem Schriftzeichenvorrat [Information technology - Representation of SI and other units in systems with limited character sets] (in German). Beuth Verlag. May 2002. Retrieved 2016-12-14.
  7. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 "Precision and Power Resistors (ISA)" (PDF). Swansea, MA, USA: Isotek Corporation / Isabellenhütte. Archived (PDF) from the original on 2017-02-07. Retrieved 2017-02-07.
  8. 1 2 3 4 5 6 7 8 9 10 11 12 "Production date code marking system according to IEC 60062, clause 5.1 Two-character code (year/month)" (PDF). Iskra Kondenzatorji. 2017. Archived (PDF) from the original on 2017-02-07. Retrieved 2017-02-07. (NB. Date codes for 2016 and 2017 are obviously wrong.)
  9. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 ГОСТ IEC 60062-2014 (PDF) (in Russian). GOST (ГОСТ). 2014.
  10. ↑ IEC 60062:1974
  11. ↑ https://webstore.iec.ch/p-preview/info_iec60062%7Bed5.0%7Den.pdf
  12. ↑ https://webstore.iec.ch/publication/25395
  13. ↑ BS 1852:1975.
  14. ↑ BS EN 60062:1994.
  15. ↑ BS EN 60062:2005.
  16. ↑ BS EN 60062:2016.
  17. ↑ http://www.worldstdindex.com/soft4/3975991.htm
  18. ↑ IS : 8186-1976 (PDF). 1977 [1976]. Archived (PDF) from the original on 2016-12-14. Retrieved 2016-12-14.
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