The standard resistor values are selected to ensure that any resistor manufactured can be marked as a valid part and sold. For 5% resistors, each value is approximately 10% larger than the previous value. Anything between 9.5 and 10.5 could be called 10 within 5%. Likewise, the 1% resistor values are 2% apart. Common capacitor values are more widely spaced because the tolerance on cheap ceramic capacitors is poor. For these, each value is 50% larger than the last. If you buy capacitors with a 5% tolerance, the values will be 10% apart.
The scales for 5% tolerance components start at 1 and go up 10% at a time. There is some rounding at the low end, for example where you go from 1.6 to 1.8. Ted Eckert American Power Conversion/MGE http://www.apc-mge.com/ The items contained in this e-mail reflect the personal opinions of the writer and are only provided for the assistance of the reader. The writer is not speaking in an official capacity for APC, MGE or Schneider Electric. The speaker does not represent APC's, MGE's or Schneider Electric's official position on any matter. "Tarver, Peter" <peter.tarver@san mina-sci.com> To Sent by: "PSTC 1" <emc-p...@ieee.org> emc-p...@ieee.org cc Subject 03/13/2007 10:24 OT: standard component values AM 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. Tarver ptar...@ieee.org CONFIDENTIALITY This e-mail message and any attachments thereto, is intended only for use by the addressee(s) named herein and may contain legally privileged and/or confidential information. If you are not the intended recipient of this e-mail message, you are hereby notified that any dissemination, distribution or copying of this e-mail message, and any attachments thereto, is strictly prohibited. If you have received this e-mail message in error, please immediately notify the sender and permanently delete the original and any copies of this email and any prints thereof. ABSENT AN EXPRESS STATEMENT TO THE CONTRARY HEREINABOVE, THIS E-MAIL IS NOT INTENDED AS A SUBSTITUTE FOR A WRITING. Notwithstanding the Uniform Electronic Transactions Act or the applicability of any other law of similar substance and effect, absent an express statement to the contrary hereinabove, this e-mail message its contents, and any attachments hereto are not intended to represent an offer or acceptance to enter into a contract and are not otherwise intended to bind the sender, Sanmina-SCI Corporation (or any of its subsidiaries), or any other person or entity. _____________________________________________________________________________ Scanned by Sanmina-SCI eShield _____________________________________________________________________________ - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.org Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.org Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
