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Standards for Labeling Electronic Component Values |
The convention which has been adopted for labeling electronic component values in the United States leads to errors and ambiguities. For example, a capacitor labeled only with the value "50" on a schematic diagram could be interpreted as either 50 pF (picofarads) or 50 µF (microfarads). The decimal point is easily obscured when printed poorly or subjected to several generations of photocopying or faxing. Thus a "5" might be read as ".5" if a speck of dirt is misread as a decimal point, or a missing decimal point would cause "1.5" to be read as "15".
International standards have been developed to minimize these errors. Using these conventions, components are always labeled by at least two digits and a letter. The included letter represents both the location of the decimal point and the abbreviation of the applicable prefix.
Thus, "1.5 megohms" or 1,500,000 ohms would be written as "1M5". The label "22K" still means 22 kilohms, but to represent 2200 ohms or 2.2 kilohms we would write "2K2". To indicate fractional values, remember that what we call the "decimal point" can also be defined as a "radix" point. Therefore, 3.9 ohms should be written "3R9". To indicate values less than 1 ohm it is probably better to write "0R5", for example, because "R5" alone might also mean the fifth resistor in the circuit. This, of course, is also true with the United States nomenclature: always write "0.1" instead of just ".1".
Capacitors will use "M" for "micro", "N" for "nano", and "P" for "pico". Thus a capacitor whose value is 4.7 µF should be written "4M7", and 22 pF may be written "22P". Where Americans would write either "1000 pF" or "0.001 µF" for the same capacitor, Europeans will write "1N0" because the value is more properly 1 nanofarad. Big filter capacitors may be indicated as "1000M" to mean 1000 µF, since switching to millifarads would only add another ambiguity.
Always remember to specify units for other measurements as well. Our power line voltage should be written "120 V" instead of "120" alone, and the current in a 60 watt light bulb is "0.5 A", not just "0.5". Only by using non-ambiguous units written in an error-free way can engineers and technicians the world over truly understand each other.
