Dave, You are correct. Years ago the Electronic Industries Association (EIA), devised a system and applied to resistors and capacitors. There is a mathematical algorithm based on the E-Series numbers.
E6 20% E12 10% E24 5% E48 2% E96 1% E192 0.5, 0.25, 0.1% Years ago, I even had a program for my HP-67 calculator that would take a desired value and show me the nearest standard value. Regards, -doug From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of David Cuthbert Sent: Tuesday, March 13, 2007 9:38 AM To: 'Tarver, Peter'; 'PSTC 1' Subject: RE: standard component values Quote: "These values were supposed to have been derived from the mathematical series of equally spacing values logarithmically for each decade." http://www.eng-tips.com/viewthread.cfm?qid=71035&page=5 Dave Cuthbert Linear Technology From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Tarver, Peter Sent: Tuesday, March 13, 2007 9:24 AM To: PSTC 1 Subject: OT: standard component values An off-topic question that hopefully someone can shed a little light upon. I have wondered for as long as I've been involved in things electrical, why standard component values are what they are. Text books are of no use and I've done more than a few internet searches on this in the last ten years (or so; maybe I've used the wrong search terms, but I haven't found an answer). I'm interested to hear what others might know or think about this arcane topic. It's probably lost to history now, but it may well be based on some limitations of physical characteristics of early devices or one manufacturer dominating the early production of components and they had some idea that they could sell more components if they were in strange increments. Or maybe there's a mathematical reason that hasn't occurred to me, like some arithmetic progression, or even simple phobias or prejudices. Maybe someone gave it the deepest thought and surmised that particular values would yield the minimum of mixing of components in series/parallel combinations. Maybe they're still laughing from the grave. Regards, Peter L. 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