John, I agree with the common sense approach and use it frequently. It's always interesting to me how I can look at a screen plot of 60 thermocouples and in a second or two decide, "yes this is stable". I can even estimate how much time it will take to become stable as a test nears the end (usually about the time of a lunch break). More than once I have attempted to write an algorithm to make the same projection and have failed every time. The non-linearities and multiple heat sources & sinks makes this nearly impossible.
On a side-bar, Voltaire is quoted as saying "*Common sense is not so common*", which mean he is man with similar sensibilities as myself. Those who know me personally have often heard me say what I consider to be a corollary, "*Common sense is usually neither.. common or sensible*". -Doug Douglas E Powell Laporte, Colorado USA doug...@gmail.com http://www.linkedin.com/in/dougp01 On Fri, Jan 6, 2017 at 11:30 AM, john Allen <john_e_al...@blueyonder.co.uk> wrote: > Minor comment: > Having been the Secretary to a number of BSI committees many years ago, I > sympathise with Ralph's last para as the Chairmen can be even worse than > the > other Members - they "know what they know" and it can take an awful lot of > "effort" to "persuade" them that they need to "think again" - once had to > refuse to publish a Chairman's version of a new standard because it did not > meet the basic BSI guidelines for how a product standard should be written, > until I had rewritten a large part of it to make it at least reasonably > "testable" for the EMC-related requirements - a little (sometimes a lot!) > of > subject knowledge is required to set appropriate test and assessment > requirements! > > Unfortunately, nowadays, a large number of Committee Secretariats appear to > employ non-SME staff to run their committees and so they can be lead by the > nose by the Chairmen. > > FWIW, in the context of this thread, I used to use "commonsense" in > deciding > when the temperatures appeared to have stabilized - -taking into account > where the probes were located - particularly when the observed > temperatures > were substantially below the relevant Insulation Class limits. > > John E Allen > W. London, UK > > -----Original Message----- > From: Ralph McDiarmid [mailto:ralph.mcdiar...@schneider-electric.com] > Sent: 06 January 2017 17:20 > To: EMC-PSTC@LISTSERV.IEEE.ORG > Subject: Re: [PSES] Thermal equilibrium - 10% rule > > For what it's worth, we measure and log temperatures at 1 minute intervals > (sometimes quicker, depending on what is being tested) and graph each data > set in Excel and look at the curves. When they go flat (even with some > ripple), we call it stable. Good enough for all the agencies we work with. > And I like the term steady-state much better, but what it is called isn't > terribly important as I see it. The temperature can be stable (no further > increase observable) over a period, even if it's oscillating slightly > around > a mean value. The mean value could be the average of the last 20 or so > reading for instance. It requires some judgement. > > I empathize with John's experience about it taking "many tellings" on a > committee to get something right. I have stopped just short of the Makita > Khrushchev United Nations technique at times! > > Ralph McDiarmid > Product Compliance > Engineering > Solar Business > Schneider Electric > > > > > > -----Original Message----- > From: Ken Javor [mailto:ken.ja...@emccompliance.com] > Sent: Friday, January 06, 2017 8:21 AM > To: EMC-PSTC@LISTSERV.IEEE.ORG > Subject: Re: [PSES] Thermal equilibrium - 10% rule > > I understand that if the system is poorly designed there can be > catastrophic > results, but the test is written assuming the equipment temperature does > equilibrate, right? > > Ken Javor > Phone: (256) 650-5261 > > > > From: John Barnes <jrbar...@iglou.com> > > Reply-To: <jrbar...@iglou.com> > > Date: Fri, 06 Jan 2017 00:06:24 -0500 > > To: Ken Javor <ken.ja...@emccompliance.com> > > Cc: <EMC-PSTC@LISTSERV.IEEE.ORG> > > Subject: Re: [PSES] Thermal equilibrium - 10% rule > > > > Ken, > > Most metals have a positive Temperature Coefficient of Resistance (TCR). > > As they get hotter, their resistivity-- and the resistance of a given > > conductor-- increases. If you have a current source (or a voltage > > source with a large series impedance) driving current through a small > > cross-section conductor with poor heat sinking for a long time, the > > conductor will go into thermal runaway-- and eventually melt in two-- > > when the current through it exceeds a certain critical value, > > depending on the ambient temperature. > > > > A. J. Rainal wrote two papers about this effect on printed circuit > > boards (PCB's) about 40 years ago: > > * Rainal, A. J., "Current-Carrying Capacity of Fine-Line Printed > > Conductors," The Bell System Technical Journal, vol. 60 no. 7, pp. > > 1375-1388, September 1981. > > * Rainal, A. J., "Temperature Rise at a Constriction in a > > Current-Carrying Printed Conductor," The Bell System Technical > > Journal, vol. 55 no. 2, pp. 233-269, February 1976. > > > > Non-resettable fuses use this principle, which is specified by the > > I^2t curves in their datasheets. > > > > You may also want to read up on Preece's Law (Fuse Equations) and > > Onderdonk's Fuse Equation. > > > > > > > > John Barnes KS4GL (retired) > > Lexington, Kentucky > > http://www.dbicorporation.com/ > > > > - > ---------------------------------------------------------------- > 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 > <emc-p...@ieee.org> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher: <j.bac...@ieee.org> > David Heald: <dhe...@gmail.com> > > ______________________________________________________________________ > This email has been scanned by the Symantec Email Security.cloud service. > ______________________________________________________________________ > > - > ---------------------------------------------------------------- > 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 > <emc-p...@ieee.org> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher: <j.bac...@ieee.org> > David Heald: <dhe...@gmail.com> > > - > ---------------------------------------------------------------- > 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 < > emc-p...@ieee.org> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher: <j.bac...@ieee.org> > David Heald: <dhe...@gmail.com> > -- Douglas E Powell doug...@gmail.com http://www.linkedin.com/in/dougp01 - ---------------------------------------------------------------- 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 <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
