Electronic color code
The electronic color code discussed here is used to indicate the values or ratings of electronic components, very commonly for resistors, but also for capacitors, inductors, and others. A separate code, the 25-pair color code, is used to identify wires in a cable or bundle.
The electronic color code was developed in the early 1920s by the Radio Manufacturer's Association, now part of Electronic Industries Alliance and was published as EIA-RS-279. The current international standard is IEC 60062[1].
Advantages of color coding (over printed text) on physically small components are the inherent increase in marking area, which makes the values easier to read without magnification, and a 360 degree viewing angle which cannot be achieved with text. Color coded markings are also more resistant to abrasion.
A significant drawback, on the other hand, is color degradation due to aging, oxidation and overheating. In the days of classical chassis televisions, for example, overheated resistors would change their color bands, making it virtually impossible to distinguish brown from red from orange, except by circuit analysis and deduction. This could mean the difference between a 330 Ω, 3.3 kΩ or 33 kΩ resistor respectively (a factor of 100). An overheated 33 kΩ resistor often looked like 330 Ω. Dirt, unusual lighting, and color blindness can also make it difficult to read color codes.
Other schemes
Color-coding of this form is becoming rarer. In newer equipment, most passive components come in surface mount packages. Many of these packages are unlabeled, and those that are normally use alphanumeric codes, not colors.
In one popular marking method, the manufacturer prints 3 digits on components: 2 value digits followed by the power of ten multiplier. Thus the value of a resistor marked 472 is 4,700 Ω, a capacitor marked 104 is 100 nF (100,000 pF), and an inductor marked 475 is 4.7 mH (4,700,000 nH). This can be confusing; a resistor marked 100 might seem to be a 100 Ω unit, and we must rely upon experience to interpret the marking as 10 Ω (10×100). Another way is to use the "kilo-" or "mega-" prefixes in place of the decimal point:
- 1K2 = 1.2 kΩ = 1,200 Ω
- 4M7 = 4.7 MΩ = 4,700,000 Ω
- 6R8 = 6.8 Ω
For 1% resistors, a three-digit alphanumeric code is sometimes used, which is not obviously related to the value at all. For instance, a resistor marked 68C is 499(68) × 100(C) = 49,900 Ω.
It is sometimes not obvious whether a color coded component is a resistor, capacitor, or inductor, and this may be deduced by knowledge of its circuit function, physical shape or by measurement (capacitors have nearly infinite resistance; unfortunately, so do faulty open-circuit resistors and inductors).
Resistor, capacitor and inductor
Resistor values are always coded in ohms, capacitors in picofarads (pF), inductors in microhenries (µH), and transformers in volts.
- band A is first significant figure of component value
- band B is the second significant figure
- band C is the decimal multiplier
- band D if present, indicates tolerance of value in percent (no color means 20%)
For example, a resistor with bands of yellow, violet, red, and gold will have first digit 4 (yellow in table below), second digit 7 (violet), followed by 2 (red) zeros: 4,700 ohms. Gold signifies that the tolerance is ±5%, so the real resistance could lie anywhere between 4,465 and 4,935 ohms.
Resistors manufactured for military use may also include a fifth band which indicates component failure rate (reliability); refer to MIL-HDBK-199 for further details.
Tight tolerance resistors may have three bands for significant figures rather than two, and/or an additional band indicating temperature coefficient, in units of ppm/K.
All coded components will have at least two value bands and a multiplier; other bands are optional (italicised below).
The Standard EIA Color Code Table per EIA-RS-279 is as follows:
| Color | 1st band | 2nd band | 3rd band (multiplier) | 4th band (tolerance) | Temp. Coefficient |
|---|---|---|---|---|---|
| Black | 0 | 0 | ×100 | ||
| Brown | 1 | 1 | ×101 | ±1% (F) | 100 ppm |
| Red | 2 | 2 | ×102 | ±2% (G) | 50 ppm |
| Orange | 3 | 3 | ×103 | 15 ppm | |
| Yellow | 4 | 4 | ×104 | 25 ppm | |
| Green | 5 | 5 | ×105 | ±0.5% (D) | |
| Blue | 6 | 6 | ×106 | ±0.25% (C) | |
| Violet | 7 | 7 | ×107 | ±0.1% (B) | |
| Gray | 8 | 8 | ×108 | ±0.05% (A) | |
| White | 9 | 9 | ×109 | ||
| Gold | ×10-1 | ±5% (J) | |||
| Silver | ×10-2 | ±10% (K) | |||
| None | ±20% (M) |
Note: red to violet are the colors of the rainbow where red is low energy and violet is higher energy.
As an example, let us take a resistor which (read left to right) displays the colors yellow, violet, yellow, brown. We take the first two bands as the value, giving us 4, 7. Then the third band, another yellow, gives us the multiplier 104. Our total value is then 47 x 104 Ω, totalling 470,000 Ω or 470 kΩ. Our brown is then a tolerance of ±1%.
Resistors use specific values, which are determined by their tolerance. These values repeat for every exponent; 6.8, 68, 680, and so forth. This is useful because the digits, and hence the first two or three stripes, will always be similar patterns of colors, which make them easier to understand.
A much older resistor color coding scheme, still to be found on components in vintage radios, is known as 'body-tip-spot'. Here the color of the resistor body was the first digit, the color of one tip or end of the resistor was the second, and the color of the spot on the body was the number of zeros.
Mnemonics
A useful mnemonic for remembering the first ten color codes matches the first letter of the color code, by order of increasing magnitude. There are many variations:
- Bad boys rape our young girls behind victory garden walls.[2][3]
- Bad boys rape our young girls, but Violet gives willingly.[2][3]
- Big boys race our young girls, but Violet generally wins.[4]
- B.B.Roy Of Great Briton had Very Good Vife
The tolerance codes, gold, silver, and none, are not usually included in the mnemonics; one extension that includes them is:
- Bad beer rots our young guts, but vodka goes well; get some now.[5]
Since B can stand for both "black" and "brown", variations are formed such as "black boys rape only young girls...".[6]
Humorous, offensive, or sexual mnemonics are more memorable (see mnemonic), but these variations are often considered inappropriate for classrooms, and have been implicated as a sign of sexism in science and engineering classes.[7] (Dr. Latanya Sweeney, associate professor of computer science at Carnegie Mellon, a black woman, mentions the mnemonic as one of the reasons she felt discriminated against and dropped out of MIT in the 1980s to form her own software company.[8][9])
An alternative way to recall that black comes before brown in the color code is to use the position of white at the end of the color code as a key to remember that its opposite, black (and not brown), is at the beginning, or to simply make a connection between black and zero (emptiness, nothingness, or absence of color).
Examples
From top to bottom:
- Green-Blue-Brown-Black-Brown
- 560 Ω ± 1%
- Red-Red-Orange-Gold
- 22,000 Ω ± 5%
- Yellow-Violet-Brown-Gold
- 470 Ω ± 5%
- Blue-Gray-Black-Gold
- 68 Ω ± 5%
Note: The sizes of the resistors depend only on the power they can dissipate, and do not affect their value.
See also
- 25-pair color code for wiring
- Other color codes
References
- ^ International Standard IEC 60062. Marking codes for resistors and capacitors. Section 3: Colour code for fixed resistors. International Electrotechnical Commission, Geneva, 5th edition, 2004.
- ^ a b Booker, M. Keith (1993). Literature and Domination: Sex, Knowledge, and Power in Modern Fiction. University Press of. ISBN 0813011957.
- ^ a b Pynchon, Thomas (1999). V. HarperCollins. p. 560. ISBN 0060930217.
- ^ Meade, Russell L. (2004). Foundations of Electronics: Circuits and Devices. Thomson Delmar Learning. ISBN 1401859763.
{{cite book}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ The Mnemonics Page - Dean Campbell, Bradley University Chemistry Department
- ^ Indiana University. Midwest Folklore (v.10-11 1960-1961 ed.).
- ^ Morse, Mary (2001). Women Changing Science: Voices from a Field in Transition. Basic Books. p. 308. ISBN 0738206156.
- ^ Roth, Mark (2005-12-26). "The Thinkers: Data privacy drives CMU expert's work". Pittsburgh Post-Gazette. Retrieved 2007-07-24.
- ^ Walter, Chip (2007-06-27). "Privacy Isn't Dead, or At Least It Shouldn't Be: A Q&A with Latanya Sweeney". Scientific American. Retrieved 2007-07-24.
External links
- 5-band Resistor Color Code Calculator
- Resistor color code calculator (Used to explore E-ranges and color codes.)
- Guide to SMD resistor codes, including alphanumeric codes