Electronic color
codes are used to indicate the values or ratings of electronic
components, very commomly for resistors, but also for capacitors,
inductors, and others.
The advantage of color coding (over printed text) on physically small
components is the inherent increase in marking AREA, which makes the
values easier to read without magnification. 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 330Ohms, 3.3KOhms or 33KOhms resistor
respectively (a factor of 100). An overheated 33KO resistor often
looked like 330Ohms. Dirt, grime, unusual lighting and color blindness
could also be a major problem.
In modern equipment, color coded components are rarely used, because
most passive components outside of integrated circuits, if there
indeed are any, come in the form of surface-mount chips (typically
0.1" x 0.1", or smaller). These tiny gray chips are too small for any
human readable markings, unless you have a microscope.
An alternative method of marking small components is to print 3 digits
on them: 2 value digits followed by the power of ten multiplier. Thus
the value of a resistor marked 472 is 4,700 ohms; a capacitor marked
104 is 100 nF (100,000 pF). This can be confusing; a resistor marked
472 might seem to be a 472 ohm unit, and we must rely upon experience
to interpret markings. Another way is to use the "Kilo" or "Mega"
prefixes in place of the decimal point:
e.g. 1K2 = 1.2K = 1200, 4M7 = 4.7M = 4 700 000.
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 ohms.
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).
Color codes are also used to identify individual wires or twisted
pairs in a multi-wire cable, particularly for telephone and digital
cables. It is simple to identify both ends of a wire by its color
coding. Cable marking is not restricted to single colors. Typically,
solid blue, say, may be used for one live conductor, while blue and
white stripes may be used for the related earth return which forms a
twisted pair with it.
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