Temperature rise is always an exponential curve. I've looked and looked for a means of predicting steady-state temperature during the initial rise of temperature from the "cold" state. It can't be done.
Once the data is reasonably complete, one can determine the constants for the curve. Because temperature rise is exponential, the temperature never achieves steady-state no matter how long the test is run. Of course, eventually the temperature change approaches infinitesimally small. I don't like steady-state determinations such as degrees change per time interval. If the part in question has a small thermal mass, or has a high thermal resistance, the temperature may never achieve a change of less than 1 C (or 1 K) regardless of the time interval. Just the circulation of air will prevent a "steady state." I like to plot the curve as the part heats. As the curve flattens, you know that you are approaching the maximum temperature. And, you immediately know whether or not the temperature, regardless of time, will exceed the maximum allowable temperature (unless, of course, the temperature is borderline to the maximum). (With today's data loggers, plotting a curve is quite easy, and doesn't require manpower to record each data point.) If the curve is well below the limit, then there is no need to be precise about a steady-state temperature. Likewise, if the curve is above the limit. The only case where steady-state temperature is critical is when the steady-state is very close to the maximum temperature. So, the standards are quite arbitrary as to what temperature change in what time interval comprises steady-state. Just follow the standard. If there is no definition of steady state, then plot the curve along with the limit line. Best regards, Rich - ---------------------------------------------------------------- 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 <emc-p...@ieee.org> 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 <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
