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Topic: component values (Read 824 times) previous topic - next topic

Yankee

This is sort of a crazy question but it's been bugging me for some time: why are the values of resistors and capacitors often in multiples of numbers like 47, 33, or 22 ? I'm sure there must be a reason for this though it could be buried in the mists of time and no one here is old enough to remember  :).

RuggedCircuits

I believe it was so tolerances on resistors would cause bands to just overlap. In the bad old days, 20% tolerance resistors were the norm. So take a 22 ohm resistor. Add 20% and you get 26.4 ohms. Now subtract 20% from 33 ohms and you get 26.4 ohms. Bingo.

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Yankee

Well that makes some sense.
But I was hoping for some really esoteric Pythagorean explanation.  ;)

retrolefty

Quote
The values given to resistors fall into a number of preferred or standard resistor values. These standard resistor values have a logarithmic sequence related to the component accuracy, enabling the standard resistor values to be spaced according to the tolerance on the component. These standard resistor values are also applicable for capacitors and other components as well as resistors.




http://www.radio-electronics.com/info/data/resistor/resistor_standard_values.php

Yankee

#4
Apr 04, 2011, 05:56 am Last Edit: Apr 04, 2011, 06:00 am by Yankee Reason: 1
Aha! So it is something mathematical. I figured I would hear something good from Lefty. ;)
That's a good site you quoted from. I'll bookmark it.

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