From: John Woodgate
Subject: Re: want a list of R value E6 E12 E24 E48 E96
Date: Mon, 11 Nov 2002 22:02:02 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Mon, 11 Nov 2002 23:00:02 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that John Jardine
wrote (in ) about 'want a list of R value E6 E12 E24 E48 E96', on Mon, 11 Nov
> Well go on then ... . I'm genuinely and honestly interested in knowing how
>the E() series were generated. There is scant info' out there and you may be
>the keeper of some interesting details. I think we should be told!.
The values ARE logarithmic, or a geometric progression, in other words.
NO BS. Not much to do with voltage dividers, though; more to do with
tolerances. Just take a crude example, a 1.2 kohm +/-10% may be any
value between 1.08 kohm and 1.32 kohm. A 1 kohm +/-10% may be any value
between 0.9 kohm and 1.1 kohm. A 1.5 kohm +/-10% may be any value
between 1.35 kohm and 1.65 kohm.
Thus IF your circuit will accept a +/-10% tolerance, one of those values
is bound to be OK (there is a small gap between 1.32 kohms and 1.35
kohms, but you can't do better with just two significant figures for the
If you actually calculate the values for the 10 % series, the ratio
should be the 12th root of 10, 1.2115... So you can't get exact 2-figure
values if you stick rigidly to that figure. The actual 'preferred
values' deviate by more than just rounding in the case of 2.7, which
'should' be 2.6, 3.3, which should be 3.2, 3.9, which should be 3.8 and
4.7, which should be 4.6. It is alleged by a reliable author (Thomas
Roddam in Wireless World) that the deviations were chosen to improve
colour contrast. (The committee, IEC TC40?, obviously didn't think
anyone would be ingenious enough to paint the resistor bodies maroon!)
He also shows how to use the log properties (to bases other than 10) to
simplify calculations of networks.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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