We have to consider that the temperatures sought are not of metrological value, but to to establish a safe/non-safe result. This means that the whole time constant discussion is relevant only when the final expected temperature is close to the standards limit value. The mathematical limit of an exponential rise is easy to estimate, once a few timed samples are available, and if that value is far enough above or below the limit, a conclusion is easy to draw.
For cyclic heating equipment, a similar approach is not difficult. If the cycle is unknown , there is no other option than to wait infinitely. Unfortunately, any cyclic information is unknown if the test engineer is not involved with the operating principle of the EUT, so if following a black box testing approach, the measurement will never get to completion ! ;<) Regards, Ing. Gert Gremmen Approvals manager ------------------------------------------------------------------------------------ + ce marking of electrical/electronic equipment + Independent Consultancy Services + Compliance Testing and Design for CE marking according to EC-directives: - Electro Magnetic Compatibility 2014/30/EC - Electrical Safety 2014/35/EC - Radio & Telecommunication Terminal Equipment 99/5/EC Web: www.cetest.nl (English) www.ce-test.nl (Dutch) www.cetest.fr (under construction) Phone : +31 10 415 24 26 ------------------------------------------------------------------- This e-mail and any attachments thereto may contain information that is confidential and/or protected by intellectual property rights and are intended for the sole use of the recipient(s) named above. Any use of the information contained herein (including, but not limited to, total or partial reproduction, communication or distribution in any form) by persons other than the designated recipient(s) is prohibited. If you have received this e-mail in error, please notify the sender either by telephone or by e-mail and delete the material from any computer. Thank you for your co-operation. From: John Woodgate [mailto:jmw1...@btinternet.com] Sent: Saturday 7 January 2017 00:32 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Thermal equilibrium - 10% rule Standards can't necessarily cover every possibility. For cyclical effects, I would say that conditions are stable if two successive temperature maxima are equal (within a reasonable tolerance). This doesn't necessarily work if more than one cycle frequency is involved, in which case you have to look for the repetition of the whole sequence, which might take a long time. For example, a 10 minute cycle and a 12 minute cycle give a sequence that repeats every 60 minutes. If you are lucky. With best wishes DESIGN IT IN! OOO – Own Opinions Only www.jmwa.demon.co.uk J M Woodgate and Associates Rayleigh England Sylvae in aeternum manent. From: Doug Powell [mailto:doug...@gmail.com] Sent: Friday, January 6, 2017 11:09 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Thermal equilibrium - 10% rule Thanks! I'll take a look. I generally log with LabView or direct into an Excel spreadsheet, maybe I can get an Excel VB Script to post expected times. One of the concerns I am dealing with now is how to determine stability when there are cyclical operations going on. I am using the prescribed stability criteria and using this on the minima/maxima of the temperature variations as it moves up and down. Funny, as I sit starting at thermal data moving in this way, I think of it "porpoise-ing" up and down. All the best, Doug -Doug Douglas E Powell Laporte, Colorado USA doug...@gmail.com http://www.linkedin.com/in/dougp01 On Fri, Jan 6, 2017 at 2:10 PM, Brian O'Connell <oconne...@tamuracorp.com> wrote: Rough pseudo code for my transformer algorithm for logging and monitoring temperatures for normal operating conditions: time constant = (material ksp * mass) / (24*60) sample interval = time constant / (mass * material kx) breakpoint flags = false if sample interval < min interval sample interval = min interval interrupts: temperatures to circular buffer log samples and windowed averages to network storage loop: for each channel verify exponential and set breakpoint flag for each channel update thermal lag time adjust sample interval if time constant > thermal lag/2 find least dT/dt channel find largest thermal lag time per ambient time per matching indices of windowed means if all breakpoint flags indicate done Brian From: Doug Powell [mailto:doug...@gmail.com] Sent: Friday, January 06, 2017 11:11 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Thermal equilibrium - 10% rule 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 - ---------------------------------------------------------------- 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> - ---------------------------------------------------------------- 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>
