Uhh well, Centigrade is a system which is prejudiced toward the world of water, setting a nice logical zero at the water freeze point and a nice metric friendly 100 at the boil point of water. If we all lived on Venus, maybe our temperature scales would be based on methane transition points. The Kelvin scale is more universal, with 0 K being the point of no molecular energy, and everything else going on above that point. It makes more sense, but it forces us to use large numbers for everyday conditions. If you like expressing temperature in degrees Kelvin, you might be a physicist.
Ed Price El Cajon, CA USA -----Original Message----- From: John Shinn [mailto:[email protected]] Sent: Tuesday, October 09, 2012 10:25 PM To: [email protected] Subject: Re: [PSES] thermal resistance - K versus C Naftali is correct in that Kelvin is an extension of °C, only offset so that 0 Kelvin is at absolute zero, or -273.15 °C. When referring to a Delta-T, the number is the same whether in Kelvin or °C. Be aware that the specs noted are Delta-T/Watt, not actual temperatures. Also, Theta JS is Junction to (heat)Sink. I don't know what a solder-point is. Please enlighten. I have not worked much with SMT, so I may be showing my age. John Shinn, P.E. -----Original Message----- From: N. Shani Sent: Tuesday, October 09, 2012 3:22 PM To: McInturff, Gary Cc: [email protected] Subject: Re: thermal resistance - K versus C K or C are (almost) identical, just the starting point is different: C starts @ 0 (freezing temperature for distilled water at sea level pressure, i.e., 1 atmosphere), and defines 100 as boiling of same conditions. K is the same as C, but is off-set by 273 (i.e., 0 K is -273 C, so 100 C is 373 K). What transformation did you use to get those weird numbers? Cheers, N. Shani Ottawa, ON On 10/9/12, McInturff, Gary <[email protected]> wrote: > Thought I knew what I was doing, obviously I don't I have a device > with a thermal resistance ThetaJA (J-P in this documentation). It's > for SMT CHIP LED the specified value is 400C/W. for a plastic package > that seems about right. I am looking at another LED but it lists > ThetaJA as 400K/W. (Kelvin/Watt) Seems pretty good as it would > convert to 126C/W - the lower the better. But then I converted the > ThetaJS (I think its junction - solder point), and that value was > 180K/W. When converted its -93C. Does the change in sign just indicate > the direction heat is flowing? ThetaJA is positive since the heat is > leaving the die through the package, and the ThetaJS is negative > because it is heating entering the die through the solder process? > > > Gary McInturff > Reliability/Compliance Engineer > > > > > > > > > Esterline Interface Technologies > > Featuring > ADVANCED INPUT, MEMTRON, and LRE MEDICAL products > > > > 600 W. Wilbur Avenue > Coeur d'Alene, ID 83815-9496 > Office:208-635-8306 > Cell: 509 868 2279 > Toll Free: 800-444-5923 X 1238 > [email protected]<mailto:[email protected]> > > > www.esterline.com/interfacetechnologies<http://www.esterline.com/advan > cedinput> > > Technology, Innovation, Performance... > > > > > - > ---------------------------------------------------------------- > 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 <[email protected]> > > 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://listserv.ieee.org/request/user-guide.html > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <[email protected]> Mike Cantwell > <[email protected]> > > For policy questions, send mail to: > Jim Bacher: <[email protected]> > David Heald: <[email protected]> > - ---------------------------------------------------------------- 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 <[email protected]> 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://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]> - ---------------------------------------------------------------- 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 <[email protected]> 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://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]> - ---------------------------------------------------------------- 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 <[email protected]> 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://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
