I’m not sure I would consider IEC 62368-1 as having entirely practical criteria. In particular, I dislike the “10%” clause. Is it 10% of the temperature measured in Kelvin or Centigrade? All of the specific references in that part of B.1.6 are to Kelvin.
“With reference to those tests that are to be continued until steady state temperatures are attained, steady state is considered to exist if the temperature rise does not exceed 3 K in 30 min. If the measured temperature is at least 10 % less than the specified temperature limit, steady state is considered to exist if the temperature rise does not exceed 1 K in 5 min.” If I have a circuit board rated 130 C, that is 403 K. There is a big difference between 10%. I presume it is 10% of the temperature in Centigrade. Just for fun, let’s presume I have an IT product that has a section that must be kept at temperatures below freezing. Off hand, I don’t have a specific cryogenic system that becomes unsafe if it gets to warm, but this is just a though experiment. If there is a part that must remain below freezing for safety, “10 % below” that negative number now means a measurement warmer than the safety limit. Admittedly, this is a somewhat outlandish though experiment, but it is a case where “10 % below” in Centigrade becomes even more problematic Ted Eckert Microsoft Corporation The opinions expressed are my own and do not necessarily reflect those of my employer. From: Jim Hulbert [mailto:jim.hulb...@pb.com] Sent: Friday, January 6, 2017 7:30 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Thermal equilibrium - 10% rule IEC 62368-1 seems to have a fairly practical criteria for thermal “steady state” (not “equilibrium”) in B.1.6. Steady state is considered to exist if the temperature rise does not exceed 3 K in 30 min. If the temperature is at least 10% below the specified limit, then steady state is considered to exist if the temperature rise does not exceed 1 K in 5 min. It is not necessary to control ambient temperature to any specific value, but the value should be monitored and recorded. Jim Hulbert From: Doug Powell [mailto:doug...@gmail.com] Sent: Friday, January 06, 2017 9:32 AM To: EMC-PSTC@LISTSERV.IEEE.ORG<mailto:EMC-PSTC@LISTSERV.IEEE.ORG> Subject: Re: [PSES] Thermal equilibrium - 10% rule I agree that thermal equilibrium can never be achieved especially in light of the zeroth law of thermodynamics, but also for more reasons than the exponential nature of the thing. Possibly a better phrase to use is thermal stability. I actually believe that the standards committees will re-use the text of previous standards and averse to changing it in subsequent revisions with the rationale that it worked in the past and possibly there's someone relying on this bit of information. The 10 percent of the previously elapsed time business simply does not make sense to me and I have never used it in actual testing. Nevertheless, it has shown up in a couple of recently published standards I use for large format storage batteries. In my case, I have an outdoor product that weighs in at more than 100,000 pounds and thermal equilibrium cannot be achieved in 24 hours, meanwhile the daily cyclical temperature compound the problem of measurement. Obviously, I am going to have to do live compensation of ambient conditions during the test and not afterward. Thanks all, Doug On Fri, Jan 6, 2017 at 12:31 AM, John Woodgate <jmw1...@btinternet.com<mailto:jmw1...@btinternet.com>> wrote: Only that , even with cooling and conductor resistivity taken into account, the approach to equilibrium is still very nearly exponential (the resistivity change is non-linear) , so in theory takes infinite time. With best wishes DESIGN IT IN! OOO – Own Opinions Only www.jmwa.demon.co.uk<http://www.jmwa.demon.co.uk/> J M Woodgate and Associates Rayleigh England Sylvae in aeternum manent. From: Ken Javor [mailto:ken.ja...@emccompliance.com<mailto:ken.ja...@emccompliance.com>] Sent: Friday, January 6, 2017 3:18 AM To: EMC-PSTC@LISTSERV.IEEE.ORG<mailto:EMC-PSTC@LISTSERV.IEEE.ORG> Subject: Re: [PSES] Thermal equilibrium - 10% rule Understand I’m not arguing with Rich Nute on a topic with which I have little familiarity. I’m just looking at the physics of heat transfer. If I am running current through a conductor that causes its temperature to rise, then as temperature rises, according to Newton’s Law of Cooling, more heat is transferred from the hot body to the cooler surroundings, in direct proportion. So at some point the temperature will equilibrate because the heat energy radiated/convected/conducted to the surroundings will equal the electrical energy dissipated in the conductor. What am I missing? Ken Javor Phone: (256) 650-5261<tel:(256)%20650-5261> ________________________________ From: Richard Nute <ri...@ieee.org<mailto:ri...@ieee.org>> Reply-To: <ri...@ieee.org<mailto:ri...@ieee.org>> Date: Thu, 5 Jan 2017 17:03:36 -0800 To: <EMC-PSTC@LISTSERV.IEEE.ORG<mailto:EMC-PSTC@LISTSERV.IEEE.ORG>> Subject: Re: [PSES] Thermal equilibrium - 10% rule Thermal equilibrium is impossible. Thermal change is an exponential, never achieving the end-point. The test is to determine that some part does not exceed its temperature rating. Plotting the (exponential) curve shows whether the temperature in question is or is not going to exceed its rating. (Curve-fitting would be nice, but impossible.) As soon as this determination is made, the test can be concluded. Defining thermal equilibrium as ±2°C (3.6°F) is not achievable as thermal change is an exponential. And, it is tight. For a small (low thermal mass) part, air currents will change the temperature beyond this limit. The statement does not reflect knowledge of primitive thermodynamics. Best wishes for the New Year! Rich From: Doug Powell [mailto:doug...@gmail.com] Sent: Thursday, January 05, 2017 2:47 PM To: EMC-PSTC@LISTSERV.IEEE.ORG<mailto:EMC-PSTC@LISTSERV.IEEE.ORG> Subject: [PSES] Thermal equilibrium - 10% rule All, The following has always been confusing for me, For those tests that require the DUT to reach thermal equilibrium, thermal equilibrium is considered to be achieved if after three consecutive temperature measurements taken at intervals of 10% of the previously elapsed duration of the test but not less than 15 min, indicate no change in temperature greater than ±2°C (3.6°F). The portion of text "taken at intervals of 10% of the previously elapsed duration of the test" has been around for some time and it exists in several safety standards, the "not less than 15 min" can be other values like 10 minutes, 5 minutes, etc. I believe the intent is to minimize the number of data points being recorded for extremely long thermal tests. The idea makes sense when I think back to the days of manual data logging. Nowadays, with the advent of automated data logging, this point probably becomes moot. Still, the phrase bugs me and I would like to understand how this might be interpreted. First the "previously elapsed duration" could indicate either the duration of the entire test or the duration of the last logging interval. Second, over a long test 10% of the previous interval very quickly shortens the logging intervals to something ridiculously small. For example, in three data points interval of 1440 minutes (24 hours) will be reduced to 144 minutes (2.4 hours) and then 14.4 minutes, at which point the 15 minute minimum takes over. I generally record at a much shorter intervals, even if for several days and check for equilibrium at a modulus of 15 minutes, as required. Thanks, Doug -- Douglas E Powell doug...@gmail.com<mailto: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<mailto: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) <http://www.ieee-pses.org/list.html><http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org<mailto:sdoug...@ieee.org>> Mike Cantwell <mcantw...@ieee.org<mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org<mailto:j.bac...@ieee.org>> David Heald <dhe...@gmail.com<mailto: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<mailto: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)<http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org<mailto:sdoug...@ieee.org>> Mike Cantwell <mcantw...@ieee.org<mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org<mailto:j.bac...@ieee.org>> David Heald <dhe...@gmail.com<mailto: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<mailto: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)<http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org<mailto:sdoug...@ieee.org>> Mike Cantwell <mcantw...@ieee.org<mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org<mailto:j.bac...@ieee.org>> David Heald <dhe...@gmail.com<mailto:dhe...@gmail.com>> -- Douglas E Powell doug...@gmail.com<mailto: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<mailto: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)<http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org<mailto:sdoug...@ieee.org>> Mike Cantwell <mcantw...@ieee.org<mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org<mailto:j.bac...@ieee.org>> David Heald <dhe...@gmail.com<mailto: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<mailto: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)<http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org<mailto:sdoug...@ieee.org>> Mike Cantwell <mcantw...@ieee.org<mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org<mailto:j.bac...@ieee.org>> David Heald <dhe...@gmail.com<mailto: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>
