Bill,
Thanks for the site.
Went there and found the same formula and constant I use.
For copper, Temp Coeff = 3.9 x 10-3
Then I clicked on table of coeff and there was a very long list of
materials, but the temp coeff of copper there was 6.8 x 10-3 ???!!!
Any ideas for this disparity?
- Robert -
Robert A. Macy, PE [email protected]
408 286 3985 fx 408 297 9121
AJM International Electronics Consultants
619 North First St, San Jose, CA 95112
-----Original Message-----
From: Bill Ellingford <[email protected]>
To: 'Colgan, Chris' <[email protected]>;
[email protected] <[email protected]>
List-Post: [email protected]
Date: Monday, May 13, 2002 5:38 AM
Subject: RE: Constant for Change of Resistance formula.
Hi Folks
Further to the answer given, here is a little more data.
The constant used is for the change of resistance with temperature. metals
and alloys (conductors) all exhibit a different constant. This can be used
for calculating temperature rise or resistance change. i.e. find the temp
rise from a start and finish test measurement on a winding (for example) at
the begining and end of a on load heat run or, find R for a given temp:
using a table or the formula, resistance at various temperatures can be
pre-determined from a measurement made at one particular temperature.
A website with the formulae can be found at
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/restmp.html
Where you have a transition from one metal type to another, you must measure
each metal part individually. If you have only two metals in contact, you
may be able to apply a combination of the temp coefficient methods and
transposition of the measurement of change of junction voltage formulae i.e.
Thermocouple laws.
Hope this adds some value: Bill Ellingford
-----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
>
>
>
>
>
>
>
>
>
>
>
>
>
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