Chris, You may be correct that I was assuming a more complex situation than the original poster intended. It won't be the first time this has happened. However, I cannot entirely agree with your "take" on the situation.
In your post you mention: >I would assume that one of the conditions of using this formula is that >the current flowing in the conductor at the time of resistance >measurement must be low enough to cause negligible heating on its own. The original poster stated that he was trying to determine the change of temperature in a connector, caused by increased resistance of its conductors. This clearly implies that the increased temperature must be due to additional resistive heating of these contacts, which in turn means that there MUST be sufficient current flowing in the connection to cause non-negligible heating. After all, if the additional heating due to current flow through a more resistive contact material was, in fact, negligible, then the connector would not get hotter, and the OP would not be worrying about "change of temperature based on change of resistance" as he stated. Bob Wilson TIR Systems Ltd. Vancouver. -----Original Message----- From: Chris Maxwell [mailto:chris.maxw...@nettest.com] Sent: May 13, 2002 2:09 PM To: Robert Wilson; emc-p...@majordomo.ieee.org Subject: RE: Constant for Change of Resistance formula. Bob, I read your initial response to this thread; and I think that your understanding of the situation is more complicated than it really is. I snipped the following from your response: > Nonetheless, you cannot possibly directly determine what the temperature > change of something as physically and geometrically complex as a > connector, merely by factoring in what its resistance change is. Among > other things, the solution is extremely non-linear and iterative. Changing > resistance will generate more heat, which will increase temperature, which > will generate even more heat ....and on and on! Add this to the fact the > resistance coefficient with temperature is itself non-linear, and you can The situation that you describe ..."changing resistance will generate more heat..." is assuming that the heating in the conductor is due to current flow, possibly as well as ambient changes. In the situation that you describe, you have temperature changing (due to current flow), which increases resistance (due to temperature change)... which increases temperature (due to increased resistance) which increases resistance (due to increased temperature)... ... I assume everyone gets the point of that train of thought, so I'll spare any more cycles. You are also assuming a complicated mechanical situation, such as a connector; where there are interfaces, differing materials... many factors that would make the math messy. So, yes, I agree that your scenario could not possibly be described by a linear equation. However, I believe that the formulae that everyone is describing deal with the change in resistance due to temperature alone. I would assume that one of the conditions of using this formula is that the current flowing in the conductor at the time of resistance measurement must be low enough to cause negligible heating on its own. Even with that, the equation is probably an approximation for small temperature changes. Your point is well taken: that is...know the limitations of any formula that you apply. To twist an old proverb: Believe half of what you see, none of what your hear and about 10% of the formulae that can be reproduced by an ASCII email :-) Chris Maxwell | Design Engineer - Optical Division email chris.maxw...@nettest.com | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
