In message <[email protected]>, dated Tue, 26 Jul 2011, Derek Walton <[email protected]> writes:
>I have to take exception to the spacing material. First rule of >assessing a lab is look for where the lab don't comply... if there's is >no criteria, you cant assume or impose anything: opinions are >irrelevant. The standards group may be working on something, but thats >of no significance: you know what assume spells don't you..... I think this raises more than one very important point. First, yes, a test house or assessor must not gold-plate the standard, i.e. make assumptions that render it more stringent. Second, even so, if they see something that raises doubts, they can ADVISE. Third, they should always report the matter through their route into the standards body; we all have one, however carefully concealed (;-) > >In my humble opinion, I'd wager that a little humidity on paper ( a >small change in a very high resistance ) has less effect than >dielectric constant ( the capacitance ) of different plastics. But the permittivity of the absorbed water is about 80 (yes, eighty), so the capacitance goes up greatly if the board is damp. >BTW, look at the dielectric strength ratings listed in MacMaster-Carr >for a bunch of their plastics. Not many are rated for 8 kv at 20 mils >thickness. PETP (such as Mylar) is very good. The spacer doesn't have to be homogenous; a combination of low-cost material (non-hygroscopic) and a plastic film might be attractive. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK When I point to a star, please look at the star, not my finger. The star will be more interesting. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://product-compliance.oc.ieee.org/ Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
