RKM code

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The RKM code, [1] also referred to as "letter and numeral code for resistance and capacitance values and tolerances", [1] "letter and digit code for resistance and capacitance values and tolerances", [2] [3] or informally as "R notation" [4] [5] [6] [7] [8] [9] is a notation to specify resistor and capacitor values defined in the international standard IEC  60062 (formerly IEC 62) since 1952. Other standards including DIN  40825 (1973), BS  1852 (1975), [10] IS  8186 (1976), and EN  60062 (1993) have also accepted it. The updated IEC 60062:2016, [1] amended in 2019, comprises the most recent release of the standard.

Contents

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 [11]
R470.47 ohm
4R74.7 ohm
470R470 ohm
4K74.7 kilohm
47K47 kilohm
47K347.3 kilohm
470K470 kilohm
4M74.7 megohm

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. [nb 3]

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. [nb 4]

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 1.2 Ω, and 18R indicates 18 Ω.

Code letter SI prefix Multiplier [12]
Resistance [ Ω ]Capacitance [ F ]NameSymbolBase 10Value
—p (P [nb 2] )picop× 10−12× 0.000000000001
—n (N [nb 2] )nanon× 10−9× 0.000000001
—μ (u, U [nb 2] )microμ× 10−6× 0.000001
Lm (M [nb 1] [nb 2] )millim× 10−3× 0.001
R (E [nb 5] )F——× 100× 1
K (k [nb 6] )—kilok× 103× 1000
M [nb 1] —megaM× 106× 1000000
G—gigaG× 109× 1000000000
T—teraT× 1012× 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 is absent from most older character encodings (though it is present in the now-ubiquitous Unicode) 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.[ citation needed ]

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, [13] 1983 [14] ), DIN 66030 (Vornorm 1973; [15] 1980, [16] [17] 2002 [18] ), BS 6430 (1983) and Health Level 7 (HL7), [19] which allow the prefix μ to be substituted by the letter u (or U) in circumstances in which only the Latin alphabet is available.

Several manufacturers of resistors utilize the RKM code as part of the components' manufacturer's part numbers (MPNs). [20] [21]

Similar codes

Though non-standard, some manufacturers also use the RKM code to mark inductors with "R" indicating the decimal point in microhenry (e.g. 4R7 for 4.7 μH). [22] [23]

A similar non-standard notation using the unit symbol instead of a decimal separator is sometimes used to indicate voltages (i.e. 0V8 for 0.8 V, 1V8 for 1.8 V, 3V3 for 3.3 V or 5V0 for 5.0 V [24] [25] [26] ) in contexts where a decimal separator would be inappropriate (e.g. in signal or pin names, in file names, or in labels or subscripts).

Tolerance code

Letter code for resistance and capacitance tolerances:

Code letterTolerance
ResistanceCapacitanceRelativeAbsolute
SymmetricalAsymmetricalC <10 pF only
AAvariable (±0.05%)variablevariable
BB±0.1%—
CC±0.25%—±0.25 pF
DD±0.5%—±0.5 pF
E±0.005%——
FF±1.0%—±1.0 pF
GG±2.0%—±2.0 pF
HH±3.0%——
JJ±5.0%——
KK±10%——
L±0.01%——
MM±20%——
N±30%——
P±0.02%——
Q—−10/+30%—
S—−20/+50%—
T—−10/+50%—
W±0.05%——
Z—−20/+80%—

Before the introduction of the RKM code, some of the letters for symmetrical tolerances (viz. G, J, K, M) were already used in US military contexts following the American War Standard (AWS) and Joint Army-Navy Specifications (JAN) since the mid-1940s. [27]

Temperature coefficient code

Letter codes for the temperature coefficient of resistance (TCR):

Code letter ppm/K
K1
L2
M5
N10
P15
Q25
R50
S100
U250
Zother

Production date codes

Twenty-year cycle code

Example: J8 = August 2017 (or August 1997)

Some manufacturers also used the production date code as a stand-alone code to indicate the production date of integrated circuits. [33]

Some manufacturers specify a three-character date code with a two-digit week number following the year letter. [34]

IEC 60062 also specifies a four-character year/week code.

Ten-year cycle code

Example: 78 = August 2017

IEC 60062 also specifies a four-character year/week code.

Four-year cycle code

IEC 60062 also specifies a single-character four-year cycle year/month code. [nb 9]

YearMonthLetter
1993
1997
2001
2005
2009
2013
2017
2021		1A
2B
3C
4D
5E
6F
7G
8H
9J
10K
11L
12M
YearMonthLetter
1994
1998
2002
2006
2010
2014
2018
2022		1N
2P
3Q
4R
5S
6T
7U
8V
9W
10X
11Y
12Z
YearMonthLetter
1995
1999
2003
2007
2011
2015
2019
2023		1a
2b
3c
4d
5e
6f
7g
8h
9j
10k
11l
12m
YearMonthLetter
1996
2000
2004
2008
2012
2016
2020
2024		1n
2p
3q
4r
5s
6t
7u
8v
9w
10x
11y
12z

Marking codes for E series preferred values

Three-character resistor marking code

For resistances following the (E48 or) E96 series of preferred values, the former EIA-96 as well as IEC 60062:2016 define a special three-character marking code for resistors to be used on small parts. The code consists of two digits denoting one of the "positions" in the series of E96 values followed by a letter indicating the multiplier.

Two-character capacitor marking code

For capacitances following the (E3, E6, E12 or) E24 series of preferred values, the former ANSI/EIA-198-D:1991, ANSI/EIA-198-1-E:1998 and ANSI/EIA-198-1-F:2002 as well as the amendment IEC 60062:2016/AMD1:2019 to IEC 60062 define a special two-character marking code for capacitors for very small parts which leave no room to print any longer codes onto them. The code consists of an uppercase letter denoting the two significant digits of the value followed by a digit indicating the multiplier. The EIA standard also defines a number of lowercase letters to specify a number of values not found in E24. [35]

Corresponding standards

See also

Explanatory 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. ↑ As different decimal separators are used depending on the locale (most commonly . and ,), and these characters are also used as thousands separators in some areas, avoiding to use decimal separators also has the advantage of not risking to become ambiguous in an international context.
  4. ↑ Alphanumerically sorting part values in RKM notation results in sorted groups of nearby values. Within some limits, this makes it easier to identify and combine similar values within these groups in preparation of a bill of materials in order to rationalize part inventory, ease part procurement and safe costs. For example, sorting the following random part values (3.3 kΩ, 4.7 kΩ, 4.7 MΩ, 3.6 kΩ, 5.1 kΩ, 3.3 Ω, 1.0 Ω, 5.6 MΩ, 9.1 kΩ) would conventionally result in a list like 1.0 Ω, 3.3 Ω, 3.3 kΩ, 3.6 kΩ, 4.7 kΩ, 4.7 MΩ, 5.1 kΩ, 5.6 MΩ, 9.1 kΩ, but would result in 3K3, 3K6, 4K7, 5K1, 9K1, 4M7, 5M6, 1R0, 3R3 in RKM code, where it is easier to spot that the values 3.3 kΩ and 3.6 kΩ as well as 4.7 kΩ and 5.1 kΩ are, depending on application, close enough to be potentially subjects for optimization.
  5. ↑ 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 (i.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.
  6. ↑ The IEC 60062 standard prescribes the usage of an uppercase Latin letter K only, however, a lowercase k is nevertheless often seen in schematics and bills of materials probably because the corresponding SI prefix is defined as a lowercase k.
  7. ↑ In order to reduce the risk for read errors, the letters G (6), I (J, 1), O (0, Q, D), Q (O, D, 0), Y, Z (2) are not used as their glyphs look similar to other letters and digits.
  8. ↑ Due to the ambiguity of many month initials (A, J, M) the code for the most part uses digits. Since letter O is easily confused with digit 0, the code is arranged so that the letter O is used for October, the tenth month, rather than for January.
  9. ↑ In order to reduce the risk for read errors, the letters I/i and O/o are not used as their glyphs look similar to other letters and digits.

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References

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  2. 1 2 International Standard IEC 60062: Marking codes for resistors and capacitors - Preview (PDF) (5 ed.). International Electrotechnical Commission. November 2004. Archived (PDF) from the original on 2022-02-10. Retrieved 2022-06-16.
  3. ↑ "14. Letter and digit code for R & C values". Units & Symbols for Electrical & Electronic Engineers (PDF). The Institution of Engineering and Technology (IET). 2016 [1985]. p. 29. Archived (PDF) from the original on 2020-08-07. Retrieved 2021-04-25. (37 pages)
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  5. ↑ vaj4088 (2016-04-13). "Controlling a Opto-Relay using Arduino". arduino.cc. Archived from the original on 2022-06-18. Retrieved 2022-06-18.
  6. ↑ "What is a "100R" resistor?". stackexchange.com. 2016-07-22. Archived from the original on 2022-06-18. Retrieved 2022-06-18.
  7. ↑ Bahn, W. (2017-09-14). "Square resistors on circuit boards?". allaboutcircuits.com. Archived from the original on 2022-06-18. Retrieved 2022-06-08.
  8. ↑ 2018 Practical Electronics - National 5 Finalised Marking Instructions (PDF). N5: National Qualifications 2019. Scottish Qualifications Authority (SQA). 2018. pp. 3, 12. Archived (PDF) from the original on 2022-06-18. Retrieved 2022-06-18. (12 pages); 2019 Practical Electronics - National 5 Finalised Marking Instructions (PDF). N5: National Qualifications 2019. Scottish Qualifications Authority (SQA). 2019. pp. 3, 10. Archived (PDF) from the original on 2022-06-18. Retrieved 2022-06-18. (11 pages)
  9. ↑ "Practical Electronics" (PDF). Bathgate Academy . West Lothian, Scotland, UK. p. 12. Archived (PDF) from the original on 2022-06-18. Retrieved 2022-06-18. (15 pages)
  10. 1 2 BS 1852:1975.
  11. ↑ "Resistors - Letters and Digit Codes. Letter and digit codes to indicating resistor values". The Engineering ToolBox. 2010. Archived from the original on 2020-06-21. Retrieved 2020-05-14.
  12. ↑ Tooley, Mike (2011-07-19). "BS1852 Resistor Coding". Matrix - Electronic circuits and components. Archived from the original on 2016-12-20. Retrieved 2020-05-14.
  13. ↑ ISO 2955-1974: lnformation processing - Representations of SI and other units for use in systems with limited character sets (1 ed.). 1974.
  14. ↑ "Table 2". ISO 2955-1983: lnformation processing - Representations of SI and other units for use in systems with limited character sets (PDF) (2 ed.). 1983-05-15. Retrieved 2016-12-14.
  15. ↑ Vornorm DIN 66030[Preliminary standard DIN 66030] (in German). January 1973.
  16. ↑ 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) (1 ed.). Beuth Verlag  [ de ]. November 1980. Retrieved 2016-12-14.
  17. ↑ "Neue Normen für die Informationsverarbeitung". Computerwoche (in German). 1981-01-09. Archived from the original on 2016-12-14. Retrieved 2016-12-14.
  18. ↑ 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  [ de ]. May 2002. Retrieved 2016-12-14.
  19. ↑ "Commonly Used UCUM Codes for Healthcare Units". HL7 Deutschland e.V. 2015-11-21. Archived from the original on 2022-10-06. Retrieved 2022-12-24.
  20. ↑ "Data Sheet General Purpose Chip Resistors RC_L series ±0.1%, ±0.5%, ±1%, ±5% Sizes 0075/0100/0201/0402/0603/0805/1206/1210/1218/2010/2512" (PDF) (Datasheet) (Version 12 ed.). Yageo. 2022-08-02. Archived (PDF) from the original on 2024-02-07. Retrieved 2024-02-07. (10+1 pages)
  21. ↑ "Standard Thick Film Chip Resistors D/CRCW e3" (PDF). Vishay Intertechnology, Inc. 2024-01-01 [2023-11-07]. Document Number: 20035. Archived (PDF) from the original on 2024-02-07. Retrieved 2024-02-07.
  22. ↑ "Technical Data 4085 - HCM0703 - High current power inductors" (PDF). Cleveland, Ohio, USA: Eaton Electronics Division. March 2016 [December 2014]. Archived (PDF) from the original on 2023-12-05. Retrieved 2023-12-06. Part marking: XXX=Inductance value in uH, R= decimal point. If no R is present then last character equals number of zeros
  23. ↑ "Why are the characters such as "4R7" or "100" printed on some products?". FAQ. TDK Corporation. 2022. Archived from the original on 2022-12-09. Retrieved 2023-12-06. These are the inductances expressed in a unit of microhenry (uH). The first two digits indicate significant figures and the third digit a multiplier. When there is an "R", it indicates a decimal point, and all numbers are significant figures.
  24. ↑ "SPM1004: 12V Input 6A Output Power Supply in Inductor (PSI2) Module" (PDF). Version 3.0. Sumida Corporation  [ de ]. 2015-07-29. Archived (PDF) from the original on 2023-12-05. Retrieved 2023-12-05. (28+1 pages)
  25. ↑ "User's Guide - Dual-Mode Bluetooth CC2564C Evaluation Board" (PDF). Texas Instruments Incorporated. December 2021 [March 2020]. p. 7. SWRU495C. Archived (PDF) from the original on 2023-12-04. Retrieved 2023-12-04. (8 pages)
  26. ↑ "L99VR02J Datasheet: Automotive linear voltage regulator with configurable output voltage having 500 mA current capability" (PDF). Revision 1. STMicroelectronics NV. December 2022. DS14076. (38 pages)
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  30. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 "Marking". Class X2: Metallized Polyester Film EMI Suppression Capacitors PHE820E, Class X2, 300 VAC (PDF). Fort Lauderdale, Florida, USA: KEMET Electronics Corporation. 2021-11-10. p. 9. F3010_PHE820E_X2_300. Archived (PDF) from the original on 2022-06-16. Retrieved 2022-06-16. (13 pages)
  31. 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.)
  32. 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. Archived (PDF) from the original on 2022-02-10. Retrieved 2022-06-16.
  33. ↑ Kurth, Rüdiger; Groß, Martin; Hunger, Henry, eds. (2021-09-27) [2011]. "Integrierte Schaltkreise". Robotron Technik (in German). Beschriftung der Schaltkreise. Archived from the original on 2021-12-03. Retrieved 2021-12-06.
  34. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 "Precision and Power Resistors (ISA)" (PDF). Swansea, MA, USA: Isotek Corporation / Isabellenhütte  [ de ]. Archived from the original (PDF) on 2017-02-07. Retrieved 2017-02-07.
  35. ↑ "Annex B: Special two-character code system for capacitors". SLOVENSKI STANDARD SIST EN 60062:2016/A1:2019 (PDF) (preview). 2019-12-01. pp. 3–4. Archived (PDF) from the original on 2022-06-17. Retrieved 2022-06-17.
  36. ↑ IEC 60062:1974
  37. ↑ BS EN 60062:1994.
  38. ↑ BS EN 60062:2005.
  39. ↑ BS EN 60062:2016.
  40. ↑ IS: 8186-1976 (PDF). 1977 [1976]. Archived (PDF) from the original on 2016-12-14. Retrieved 2016-12-14.
  41. ↑ TGL 31667: Bauelemente der Elektronik; Kennzeichnung; Herstellungsdatum [TGL 31667: Electronic Components; Designation; Date of Manufacture](PDF) (in German). Leipzig, Germany: Verlag für Standardisierung. October 1979. Archived (PDF) from the original on 2021-01-28. Retrieved 2018-01-09.
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