I don't know about no longer being allowed in commercial products, but they are also ideal where they may be subject to short term overload, which is why they are often found in the leads of CRTs where they help protect the upstream circuitry in the event of tube flashover. I'd be surpirsed to find anything else in this application, although that market will die as we all move over to flat panels. Best regards
Neil R. Barker CEng MIET FSEE MIEEE Manager Quality Engineering e2v technologies (uk) ltd 106 Waterhouse Lane Chelmsford Essex CM1 2QU UK Tel: (+44) 1245 453616 Fax: (+44) 1245 453571 Mob: (+44) 7801 723735 P Please consider the environment before printing this email. From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: 14 March 2007 14:30 To: emc-p...@ieee.org Subject: Re: OT: standard component values I have heard that carbon composition resistors are no longer allowed to be used in commercial products because they burn when mistreated. I can personally attest to that, but I keep a bunch around because they are excellent resistors at high frequencies. From: "Price, Ed" <ed.pr...@cubic.com> List-Post: emc-pstc@listserv.ieee.org Date: Wed, 14 Mar 2007 06:08:37 -0800 To: emc-p...@ieee.org Subject: RE: OT: standard component values From: John Woodgate [mailto:j...@jmwa.demon.co.uk] Sent: Wednesday, March 14, 2007 1:37 AM To: emc-p...@ieee.org Subject: Re: OT: standard component values In message <45f7a47b.2040...@dctolight.net>, dated Wed, 14 Mar 2007, Fred Townsend <f...@dctolight.net> writes: >Gentlemen what you say may apply to some components but with regard to >5, 10, and 20% composition resistors it is dead wrong. The question was where the 'preferred values' came from. Not how carbon composition resistors are made and marketed now. I decided to see just what the pricing differential really was for 1%, 2%, 5%, 10% & 20% resistors, so I grabbed my Mouser catalog (the Newark and Allied catalogs were too heavy to lift) and started looking for a plain old 1/2 Watt carbon comp resistor. In ten minutes, I'm feeling like a dinosaur that can't find his swamp. Looks like component manufacturing has come a long way in 35 years or so. <g> Manufacturing variations must be capable of being held much tighter, and pricing by value tolerance is difficult to find. (So are carbon comp resistors.) I did find some examples; for instance, Kemet ceramic chip capacitors, 1000 uF, 100 VDC, pricing each, 2% @ $2.11 / 5% @ $0.18 / 2% @ $0.12. Since the manufacturing process has obviously improved, maybe we need to tighten our definition of "high accuracy." Instead of trying to find a price differential between 2% and 10% parts, I wonder what the price would be for 0.1% versus 0.5% parts? Apparently, existing circuit design practices don't typically require these tight tolerances, so the parts dealers are not featuring them. Back during my time of manufacturing components, I readily admit that our process control was primitive, and a bell-curve distribution would often have been welcome. I often had production runs where the overall yield was 30% (after physical, hipot, DF, IR, ESR and tolerance tests had each taken their bite). To get back to the original question, the component value system was set up in a time of relatively poor process control which produced a wide distribution. The progressive value system made a wide value selection available to the user, and allowed the manufacturer to sell all he made (assuming all other parameters were OK). If the user needed tighter tolerance, he could either pay a premium per part cost, or he could buy a bunch of wide tolerance parts and add his own labor to sort and/or adjust the parts into the needed tolerance. Today (aside from some small capacitors that are rated -20% / +80%) you almost can't find 20% parts; from what I saw in the catalog, 5% or even 2% is the new "plain vanilla" tolerance bracket. BTW, does anyone know when component manufacturers started using this tolerance progression? From my own observation, the system was in place for 1930's era design. Was it codified under some old EIA standard, or is it even older? Ed Price ed.pr...@cubic.com NARTE Certified EMC Engineer & Technician Electromagnetic Compatibility Lab Cubic Defense Applications San Diego, CA USA 858-505-2780 (Voice) 858-505-1583 (FAX) Military & Avionics EMC Is Our Specialty ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________ Sent by E2V TECHNOLOGIES PLC or a member of the E2V group of companies. A company registered in England and Wales. Company number: 04439718. Registered address: 106 Waterhouse Lane, Chelmsford, Essex, CM1 2QU, UK. - ---------------------------------------------------------------- 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
