2 questions. 1) HP software for 7400A analyzers, 2) FDA letters of Accession
1) I believe someone out there commented on using the HP 74XX series analyzer for pre-compliance measurements. Do you also use the additional software that can be purchased? The unit I played with had no additional software, but I could make measurements against limits lines etc, and it factored in the transceiver gains/losses and then allowed me to export a summary sheet for any reports I wanted to generate. What functions and value does the additional software bring to the table.? 2) Does anybody out there get any traction from a "Letters of accession" that the FDA sends to a optics vendor after receiving a request for a model addition? This letter says nothing useful for NRTL's and always includes "This acknowledgement does not constitute approval or the document". The FEDS are disavowing any level of conformity assessment, and the NRTL's I use tell me they can't use it, even for an unrecognized componet, yet the vendors are insistent that I am the only unaccepting curmudgeon in the entire universe. Sorry if you've heard this before but I just can't believe it keeps happening, and that tells me that I should double check my facts. Thanks Gary --- 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"
RE: Constant for Change of Resistance formula.
Stating the proven principles of accurate thermal analysis is hardly "muddling the knowledge pool". No one has suggested that increased resistance leads to increasing heat generation in an infinite spiral as you mention. This would obviously be nonsense, and is not predicted by theory or observed in practice. As I mentioned in an earlier post, increased resistance DOES lead to increased heat generation, which DOES in turn cause further resistance increase ...but this does not spiral on to infinity for the very reason that the system is nonlinear. Thermal issues ARE highly nonlinear. What DOES happen is that a new higher temperature plateau is reached where (as I wrote in my original post on this subject): "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." The bottom line is that heat transfer issues are unavoidably complex and require iterative solutions for accurate answers. That is why thermal analysis software is so hideously expensive, and requires such long times and high computer "horsepower" to converge on an accurate solution. While it may be possible to arrive at an approximate solution, for a limited set of parameters under a narrow subset of conditions by using rule-of-thumb simplification, it doesn't change the fact that an accurate solution is unavoidably far more complicated than you are presenting, and such a simplification must be understood to be just that: a simplification. Bob Wilson TIR Systems Ltd. Vancouver. -Original Message- From: Sam Davis [mailto:sda...@ptitest.com] Sent: May 14, 2002 8:57 AM To: emc-p...@majordomo.ieee.org Subject: RE: Constant for Change of Resistance formula. OK, I've avoided jumping in on this exhausted thread, but here's my take on the situation. It's obvious that more than a few of the posters have not performed this test. When you cannot answer a question with more than a theory, don't throw it out there as fact. You muddle the knowledge pool. First off, why go to the trouble of performing the CoR measurements on a connector, when you can fairly accurately (and much more simply) use a thermocouple. If you decide you need the accuracy of the Change of Resistance measurement, the equipment used for this test is specialized and highly precise, (it's a milliohm meter, not your standard DMM). The meters I've used have been capable of measuring fractions of milliohms, down to microohms. And you do end up measuring the resistance of the leads. That's why you measure them separately, in the ambient, and subtract them from the system resistance in the formula to get the resistance of the EUT only. Also, there is specially designed equipment to perform this test while the EUT is energized, but the normal method is to run the EUT until thermal stabilization, disconnect power, and measure the resistance as it drops over time, and extrapolate back to time 0. The smaller the EUT, the faster you need to get the first measurement, and subsequent measurements because within seconds, the EUT could drop significantly, making your extrapolation inaccurate. And about the resistance to temp rise to resistance rise to temp rise - if it went on infinitum, all conductors (not just those under test) would eventually ignite. This only happens when you allow too much current. Sam Disclaimer - Sorry if I stepped on any toes, but I've got big feet. --- 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" --- 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: htt
Re: Lightning and power cross in Japan
Hello Joe, In reply to your TREG message of May 14 regarding lightning incidence in Japan and any protection requirements on telecom equipment, here are several resources that you might find helpful. The Colorado Lightning Research Center focuses mostly on lightning in the U.S.A., but their Web site shows a map of lightning incidence worldwide. This map shows Japan as having lightning incidence of around 8-20 flashes/sq km/year (if I am interpreting their map correctly), which is similar to the midwestern U.S.A. or southern Canada. See: http://www.crh.noaa.gov/pub/ltg.html The National Lightning Safety Institute also has a map showing lightning strike regions in Japan, with data on the average number of thunderstorms per year at: http://www.lightningsafety.com/nlsi_info/lightningmaps/JPNghtning.html You might also check out the Web site of the Society of Atmospheric Electricity of Japan at: http://lightning.pwr.eng.osaka-u.ac.jp/saej/e_index.html NTT (Japan) standardization activities are discussed in their "NTT Review" periodical. It seems to me that this might be a place where research on lightning effects on telecom equipment in Japan might be reported. The NTT Review is available on the web at: http://www.ntt.co.jp/RD/Enindex.html Hope you find these helpful. Best regards, -- Scott Roleson - Scott Roleson, PE (MS-61U74) | E-mail: srole...@ieee.org Telecom & EMC Engineer | http://www.roleson.com Corporate External Standards | Telephone: +1-858-655-4809 Hewlett-Packard Company| FAX: +1-858-655-5931 16399 W. Bernardo Drive| Amateur Radio: KC7CJ San Diego, CA 92127-1899 USA | Any opinions are my own, not HP's. -
Lightning and power cross in Japan
Hello All: I am trying to determine whether there are any published requirements for lightning immunity or power cross for wireline PSTN terminal equipment in Japan. The JATE requirements for PSTN terminal equipment do not contain any such tests, and I am not aware of any similar requirements imposed by various industry specifications. Do any of you know of any specific requirements for Japan? On a related note, how severe is the actual lightning environment in Japan, compared to say, North America or Europe? Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 http://www.randolph-telecom.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: 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"
RE: Constant for Change of Resistance formula.
OK, I've avoided jumping in on this exhausted thread, but here's my take on the situation. It's obvious that more than a few of the posters have not performed this test. When you cannot answer a question with more than a theory, don't throw it out there as fact. You muddle the knowledge pool. First off, why go to the trouble of performing the CoR measurements on a connector, when you can fairly accurately (and much more simply) use a thermocouple. If you decide you need the accuracy of the Change of Resistance measurement, the equipment used for this test is specialized and highly precise, (it's a milliohm meter, not your standard DMM). The meters I've used have been capable of measuring fractions of milliohms, down to microohms. And you do end up measuring the resistance of the leads. That's why you measure them separately, in the ambient, and subtract them from the system resistance in the formula to get the resistance of the EUT only. Also, there is specially designed equipment to perform this test while the EUT is energized, but the normal method is to run the EUT until thermal stabilization, disconnect power, and measure the resistance as it drops over time, and extrapolate back to time 0. The smaller the EUT, the faster you need to get the first measurement, and subsequent measurements because within seconds, the EUT could drop significantly, making your extrapolation inaccurate. And about the resistance to temp rise to resistance rise to temp rise - if it went on infinitum, all conductors (not just those under test) would eventually ignite. This only happens when you allow too much current. Sam Disclaimer - Sorry if I stepped on any toes, but I've got big feet. --- 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" --- 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"
KOREAN S MARK REQUIREMENTS
Does anybody know how to achieve compliance with the Korean S mark legislation? Ian Gordon _ This message has been checked for all known viruses by UUNET delivered through the MessageLabs Virus Control Centre. For further information visit http://www.uk.uu.net/products/security/virus/ --- 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"
RE: Constant for Change of Resistance formula.
Robert, Perhaps your take on the situation is indeed on target. I'm not sure myself if I would use the formula in the situation that you describe. >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. Too many variables...current is still flowing...causing heating and dynamic resistance change...connectors have mating surfaces...which dominate the resistance. I didn't see terms in the formula that took these factors into account. Another problem that I can see with this is measuring the resistance in the first place. Most connectors have a resistance which is a fraction of an Ohm...You would almost need a bridge or other high precision device to measure in the first place; and even then you would mostly be measuring the resistance of the interface, not the contacts themselves. I never let pride stand in the way of the facts...I'm starting to lean toward your way of thinking on this one. Chris --- 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"
RE: Constant for Change of Resistance formula.
Hi Robert, Group Yes, this is a known factor for mis-measurement. You must always isolate the component part / winding etc and measure each resistive element to find the individual temperature rises. This is common practice when measuring motor windings, you would take a sample of windings measuring at the brush caps (hot brushes quickly removed) at pre-marked segments on the commutator. This allows you to get a picture of the heat characteristics of a number of windings and hence heat spread throughout the motor windings. Yes, accuracy depends on the resistance being measured but where the formula is applied (motors, relay coils, transformers, solenoids and other mechelec devices), the resistance is high enough to get a good result as long as you follow the guidelines (like those above). Thanks for raising the measurement factors. Bill Ellingford -Original Message- From: Robert Macy [mailto:m...@california.com] Sent: 14 May 2002 02:00 To: Bill Ellingford; emc-p...@majordomo.ieee.org Subject: Re: Constant for Change of Resistance formula. Bill, Big oops. Measuring the resistance to determine the temperature is not productive *unless* the resistance dominates the resistance measurement. Picture three equal valued resistances in a row. The middle one gets very hot (more than 100C rise) and increases over 40%, the two on the edges are heat sinked and barely increase in temperature. The resulting change in resistance is 13% which implies the temperature in there has only gone up around 33C. Measuring the resistance doesn't tell you much. At least with transformers the dominant resistance is pretty much the bulk resistance. - Robert - -Original Message- From: Bill Ellingford To: 'Robert Macy' ; emc-p...@majordomo.ieee.org List-Post: emc-pstc@listserv.ieee.org Date: Monday, May 13, 2002 1:56 PM Subject: RE: Constant for Change of Resistance formula. > >Hi Robert / group >OK, Not the best choice of website to demo the answer. The differing >figures are because the formula has been transposed to give Temp from change >of R from the original formula which gives R from change of T. To do this, >another constant (The 234.5 constant) is required. This is the implied >point of zero resistance for copper on the Celsius scale. The formula we >use is: > > Rfinal - Rorig > x (234.5 + Tamb start) -(Tamb finsh - Tamb start) > Rorig > >The Tamb start and finish are the changes (if any) in Room ambient. If the >room remains at 20c then 234.5 + 20 is the multiplier. > >-Original Message- >From: Robert Macy [mailto:m...@california.com] >Sent: 13 May 2002 14:54 >To: Bill Ellingford; emc-p...@majordomo.ieee.org >Subject: Re: Constant for Change of Resistance formula. > > >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, PEm...@california.com > 408 286 3985 fx 408 297 9121 > AJM International Electronics Consultants > 619 North First St, San Jose, CA 95112 > > >-Original Message- >From: Bill Ellingford >To: 'Colgan, Chris' ; >emc-p...@majordomo.ieee.org >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:chris.col...@tagmclaren.com] >Sent: 13 May 2002 10:28 >To: emc-p...@majordomo.ieee.org >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 r
RE: Constant for Change of Resistance formula.
The formula for calculating the temperature rise of a winding can be found in Annex E of IEC 60950 - and all the experts in TC 74 can't be wrong ?? (I also found the same formula in my 1985 issue of IEC 380. Different temperature coefficents for copper have been quoted, and as far as I can determine, the reason for this is as follows: Definition of "temperature coefficent of resistance" is "the ratio of the increase of resistance per degree C rise of temperature to the resistance at 0 degrees C", and for a "standard annealed copper conductor", this is 1/234.5 = .004264. However, "the ratio of the increase of resistance per degree C rise of temperature to the resistance at 20 degrees C" is apparently .00393. Regards, John Crabb, Development Excellence (Product Safety) , NCR Financial Solutions Group Ltd., Discovery Centre, 3 Fulton Road, Dundee, Scotland, DD2 4SW E-Mail :john.cr...@scotland.ncr.com Tel: +44 (0)1382-592289 (direct ). Fax +44 (0)1382-622243. -Original Message- From: Robert Macy [mailto:m...@california.com] Sent: 13 May 2002 14:54 To: Bill Ellingford; emc-p...@majordomo.ieee.org Subject: Re: Constant for Change of Resistance formula. 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, PEm...@california.com 408 286 3985 fx 408 297 9121 AJM International Electronics Consultants 619 North First St, San Jose, CA 95112 --- 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"
Fw: Sr. EMC/EMI engineer position
Hello All -- Any EMC specialist interested in working in Milpitas, California, may want to contact the following recruiter (do not contact me!). Apparently some knowledge of product safety and NEBS compliance also would be useful. Good luck! Regards, John McBain - Original Message - From: Isaac Ohana Sent: Monday, May 13, 2002 4:03 AM Subject: Sr. EMC/EMI engineer Hello John, Thank you for your time today. I look forward to talk your friends and to work with you in the future. Best Regards, Isaac Ohana Sr. Technical recruiter Davis Search Group 416-782-7191 ext.211 www.davissearch.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: 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"
Re: Constant for Change of Resistance formula.
Bill, Big oops. Measuring the resistance to determine the temperature is not productive *unless* the resistance dominates the resistance measurement. Picture three equal valued resistances in a row. The middle one gets very hot (more than 100C rise) and increases over 40%, the two on the edges are heat sinked and barely increase in temperature. The resulting change in resistance is 13% which implies the temperature in there has only gone up around 33C. Measuring the resistance doesn't tell you much. At least with transformers the dominant resistance is pretty much the bulk resistance. - Robert - -Original Message- From: Bill Ellingford To: 'Robert Macy' ; emc-p...@majordomo.ieee.org List-Post: emc-pstc@listserv.ieee.org Date: Monday, May 13, 2002 1:56 PM Subject: RE: Constant for Change of Resistance formula. > >Hi Robert / group >OK, Not the best choice of website to demo the answer. The differing >figures are because the formula has been transposed to give Temp from change >of R from the original formula which gives R from change of T. To do this, >another constant (The 234.5 constant) is required. This is the implied >point of zero resistance for copper on the Celsius scale. The formula we >use is: > > Rfinal - Rorig > x (234.5 + Tamb start) -(Tamb finsh - Tamb start) > Rorig > >The Tamb start and finish are the changes (if any) in Room ambient. If the >room remains at 20c then 234.5 + 20 is the multiplier. > >-Original Message- >From: Robert Macy [mailto:m...@california.com] >Sent: 13 May 2002 14:54 >To: Bill Ellingford; emc-p...@majordomo.ieee.org >Subject: Re: Constant for Change of Resistance formula. > > >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, PEm...@california.com > 408 286 3985 fx 408 297 9121 > AJM International Electronics Consultants > 619 North First St, San Jose, CA 95112 > > >-Original Message- >From: Bill Ellingford >To: 'Colgan, Chris' ; >emc-p...@majordomo.ieee.org >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:chris.col...@tagmclaren.com] >Sent: 13 May 2002 10:28 >To: emc-p...@majordomo.ieee.org >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:chris.col...@tagmclaren.com >* http://www.tagmclaren.com > > > > >> -Original Message- >> From: Robert Wilson [SMTP:robert_wil...@tirsys.com] >> Sent: Friday, May 10, 2002 7:00 PM >> To: emc-p...@majordomo.ieee.org; 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 w
