Those interested, i cleaned up my temperature prediction spreadsheet and if you want to play with it, let me know. The math is crude, it might even have small errors.
The spreadsheet is prepopulated in column E with data from an calculated RC network with source (green area), that you can erase, or use it to play with base data. The data is rounded to a settable number of digits. Best performance at time sampling of tau/50 and 2 digits minimum of resolution of the temperature ( x.xx degrees). At 3 digits the prediction is spectacular. Accuracy won't impact the results. It's the resolution that counts. With 1 digit of resolution the results are not very usable in terms of calculation, however your experienced engineers eye may draw conclusions anyway. After an arbitrary number of samples, the sheet calculates the final temperature tau , end of test time and creates a graph. 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 Allen [mailto:jral...@productsafetyinc.com] Sent: Monday 9 January 2017 05:19 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Thermal equilibrium - 10% rule The subject itself can easily be a presentation at ISPCE. Doug, what you and Gert have done should be a formal paper. Please consider collaborating and making it happen. John ________________________________________ From: Pete Perkins <00000061f3f32d0c-dmarc-requ...@ieee.org> Sent: Sunday, January 8, 2017 9:33 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Thermal equilibrium - 10% rule Doug, A great approach; it would make for an interesting ISPCE/PSES presentation and a paper. Go for it. :>) br, Pete Peter E Perkins, PE Principal Product Safety & Regulatory Affairs Consultant PO Box 23427 Tigard, ORe 97281-3427 503/452-1201 p.perk...@ieee.org From: Doug Powell [mailto:doug...@gmail.com] Sent: Sunday, January 8, 2017 10:39 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Thermal equilibrium - 10% rule Richard, I have tried a number of approaches in the past. Given that most products are quite complex with regard to all the potential heat sources/sinks and interfaces I decided that anything along the lines of FEA is impractical. I also tried the time constants idea which is analogous to RC time constants. I found this works well enough if you have a good amount of history with the product itself. Otherwise, due to the non-linear nature of the problem, it is difficult to predict end time or temperature until 3 to 4 time constants have already passed. I tried using the slope of ΔT to estimate when the end of the test is pending. The next attempt was to dig in a little following the equations V = Voe-(t/RC) and V = Vo[1-e-(t/RC)] where I substitute V for the the various temperatures (Vo = the absolute value of the temperature delta from start to end), C is analogous to product mass and R is the Rtheta of the product. With a little testing history, you can assume the composition of the product is similar for other products designed by the same company (copper, steel, plastics, air, liquids, etc), I solved for RC and then rearranged the algebra to solve for t which is time. There are a couple of problems in that I am still unable to come up with a general purpose solution. First this is a simultaneous solution of several unknowns which is not conducive to quick on the fly solutions. This is especially true when you are in the early stages of a temperature run when things are still moving quickly. As you know extrapolating outside an existing dataset is risky, especially when nonlinearities are invo! lved. I am now going back to basics. Q = Cp * m * abs(T2-T1) q = heat energy in Joules m = mass of the product Cp = specific heat of the product T1 = The initial temperature of the product at the start T2 = The final temperature of the product abs() is used to correct for heating or cooling With the start/final temperatures and mass taken from prior tests I can extract a Cp for a particular product. Understanding one watt is Joules/second you can factor into the equation time. My thought is that the composition of a product from the same engineering group with have similar ratios of copper, iron, plastics, etc. And then I may be able to solve for total test time or final temperature. Not forgetting that the air mass and equipment of the environmental chamber is part of the big picture. I have not fully tested this method yet, but so far I remain hopeful. If this works, I plan to build a small database of product Cp values. I would be interested to know if anyone else gives this a go and how as yet undiscovered problems are overcome. -Doug Douglas E Powell Laporte, Colorado USA doug...@gmail.com http://www.linkedin.com/in/dougp01 On Sat, Jan 7, 2017 at 12:51 PM, Richard Nute <ri...@ieee.org> wrote: > We have to consider that the temperatures sought are not of > metrological value, but to > to establish a safe/non-safe result. Yes! > The mathematical limit of an exponential rise is easy to > estimate, once a few timed samples are available, I haven't been able to come up with an equation, even though I have tried and sought help from folks who are more knowledgeable than me in the field of thermodynamics. Please tell us your methodology. Best wishes for the New Year! Rich - ---------------------------------------------------------------- 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> - ---------------------------------------------------------------- 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>
