Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!crdgw1!uunet!sco!gorn!deeptht!spcecdt
From: spcecdt@deeptht.santa-cruz.ca.us (John DuBois)
Newsgroups: sci.electronics
Subject: How were component values selected?
Message-ID: <1991May19.020604.13608@deeptht.santa-cruz.ca.us>
Date: 19 May 91 02:06:04 GMT
Organization: The Armory
Lines: 34


     I've been trying to figure out how the lists of valid component values
for parts of various tolerance were generated.  It seems to me that the
process for coming up with a list of, for example, 5% tolerance parts would
be this: 

First, determine how many steps there should be.
For 5% parts, you want to space them 10% apart, so the number of values for
a particular order of magnitude will be log1.1(10) ~ 24.159.  Round that
to the nearest integer and you get 24.  So far so good; there are indeed 24
values per order of magnitude for 5% components.

Next, determine the multiplier for each step.  10^(1/24) ~ 1.10069.
Start with 10^n and multiply by 1.10069 for each step, rounding to get the
component value for that step.

I tried that, and it doesn't work. Some values are too high and some too
low, so it isn't a matter of having a slightly incorrect multiplier, or
truncating vs. rounding.  I did try truncating the value to be used in the
next step to various numbers of decimal places, and some values are always
too high and some too low.

It occured to me that the 5% list might be based on filling in the gaps in
the 10% list, and that on the 20% list.  The 10% list should be exactly the
same as every other value in the 5% list, and similarly for the 20% list,
but this might not be the case if some odd truncation is done at each step,
so I tried everything for 10% and 20% too and still couldn't get the same
values as the standard list.

So, does anyone know how the standard list came to be?

	John
-- 
John DuBois	spcecdt@deeptht.santa-cruz.ca.us	KC6QKZ