If you plot resistance of copper vertically, against temperature horizontally, and extend the graph backwards, the point of intersection with the horizontal axis is found to be -234.5 degrees C.
(Got this out of my early years text book which I keep at my desk !) "Hence for a standard copper conductor having a resistance of 1 ohm at 0 degrees C, the variation of resistance over a range of 234.5 degrees C is 1 ohm". Regards, John Crabb, Development Excellence (Product Safety) , NCR Financial Solutions Group Ltd., Discovery Centre, 3 Fulton Road, Dundee, Scotland, DD2 4SW E-Mail :[email protected] Tel: +44 (0)1382-592289 (direct ). Fax +44 (0)1382-622243. -----Original Message----- From: Colgan, Chris [mailto:[email protected]] Sent: 13 May 2002 10:28 To: [email protected] Subject: RE: Constant for Change of Resistance formula. Ned is referring to the constant used in the "temperature rise calculated by change in resistance formula" ie <<...>> Where dt is the temperature rise, R1 is start resistance, R2 is end resistance, T1 is start ambient and T2 is end ambient. 234.5 is the formula constant for copper. This formula is used extensively when heat testing transformers and coils. I'm afraid I don't know the constant for brass but I believe the figure may be related to the "inferred absolute zero" of a material. Try asking a metallurgist? Regards Chris Colgan Compliance Engineer TAG McLaren Audio Ltd The Summit, Latham Road Huntingdon, Cambs, PE29 6ZU *Tel: +44 (0)1480 415 627 *Fax: +44 (0)1480 52159 * Mailto:[email protected] * http://www.tagmclaren.com > -----Original Message----- > From: Robert Wilson [SMTP:[email protected]] > Sent: Friday, May 10, 2002 7:00 PM > To: [email protected]; Ned Devine > Subject: RE: Constant for Change of Resistance formula. > > What are the units? 234.5 ...what?? Looking at what the units are, will > basically tell you exactly what the property is related to. > > > > 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 > see how this complicates things further. The final temperature that the > "system" stabilizes at, is reached when the logarithmically increasing > (i.e. also very non-linear) heat transfer to the environment caused by > increasing temperature, balances increased heat being generated. > > > > To reach a solution, you need to iterate your calculations, where the > results of one calculation are plugged as variables into the next > iteration. Typically a thermal analysis program will require several > hundred iteration before a converged solution results. > > > > Bob Wilson > TIR Systems Ltd. > Vancouver. > > -----Original Message----- > From: Ned Devine [mailto:[email protected]] > Sent: May 10, 2002 8:29 AM > To: [email protected] > Subject: Constant for Change of Resistance formula. > > > > Hi, > > > > Does any one know how the constant for CoR formula was determined? I know > the K is 234.5 for copper and 226 for aluminum, but what property is this > related to? > > > > I am trying to determine the change in temperature of a connector, based > on the change of resistance. The connector contacts are made of brass. > > > > Thanks > > > > Ned > > > > > > Ned Devine > Program Manager > Entela, Inc. > 3033 Madison Ave. SE > Grand Rapids, MI 49548 > 1 616 248 9671 Phone > 1 616 574 9752 Fax > [email protected] e-mail > > Entela, Inc. A Certified Woman Owned Business > www.entela.com ------------------------------------------- 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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"
