standard resistance values (logarithmic scale)

jonw · 2007-02-04 05:42

Hi· Can· any help me with this question.· What number or what scale do I use to generate the 10% preferred or standard resistor values?
··· jonw

Bruce Bates · 2007-02-04 09:29

jonw -

I'm not sure what you mean by a scale or number. I generally use a table like that below for referencing all the various standard resistor values:
http://www.sizes.com/materls/resistorVal.htm

Regards,

Bruce Bates

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Tracy Allen · 2007-02-04 17:21

Well, there are 12 resistance values in the 10% series, with signfificant figures 10,12,15,18,22,27,33,39,47,56,68,82.

The logarithmic scale with 12 values is based on 10^(k/12) for values of k from 0 to 11. Those are to be rounded off to the nearest integer. But when you do that, you will find it generates the series 10,12,15,18,22,26,32,38,46,56,68,83. There is a discrepancy in the values in the middle. This is a historical accident, simply a matter of convention. The same discrepancy happens in the 5% resistor series. However, the 1% resistor series is exact and follows the rule 10^(k/96) for k=0 to 95, rounded off to an integer. There are no discrepancies.

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Tracy Allen
www.emesystems.com

Tracy Allen · 2007-02-05 00:17

Here is a little Stamp program that generates the 96 values of the 1% resistor series.

'{$STAMP BS2pe}
'{$PBASIC 2.5}
'  generates the 1% resistor sequence
' Tracy Allen, EME Systems
root96 CON 63983    ' 65536/[noparse][[/noparse]10^(1/96)], nintysixth root of ten
wx VAR WORD   ' for high precision calculation
wy VAR WORD   ' resistance values rounded off to 3 digits
idx VAR WORD
idx0 VAR idx.BIT0  ' for trick, empirical for best result

wx=65000
FOR idx=1 TO 97    ' 96 values plus one in the next decade 100-->1000
wy=wx     + 32 - idx0 / 65
' DEBUG DEC 97-idx, TAB,DEC wx,TAB
DEBUG DEC wy,CR
wx = wx ** root96 + idx0
NEXT
END

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Tracy Allen
www.emesystems.com

standard resistance values (logarithmic scale)

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