On Sat, 16 Oct 2004, Sebastian Garcia wrote: > Peter L. Peres wrote: >> >> On Thu, 14 Oct 2004, Sebastian Garcia wrote: >> >>> I know that it works doing so. But again, the oven free response is >>> exponential, and it's impossible to fit in the paste manufacturer's >>> recommended error margin for the thermal profile. Moreover, the >>> plateau-shaped profiles were developed at the earlier days of reflow >>> soldering, when the ovens where provided only with IR heaters. Today, >>> the recommended profile for convection ovens replaces the plateau zone >>> with a slope shape. >> >> The oven response is essentially linear if the heaters are significantly >> hotter than the oven (this is true when you turn the heaters full on in a >> toaster oven). > > > As i said in my first post, i measured the oven temperature step response > (full power) with thermocouples (in air) and plotted the data... exponential. > I can understand if you *approximate* as linear the first seconds of the > exponential, but i see no reason for a linear temperature response in a > "standard" oven. I think the measurement is affected by convection which would explain the exponential part after a few seconds. Otherwise with the heaters red hot at 800+ deg C and the object to be heated under 250C it should be fairly linear. Hmm, maybe an ir oven is linear, but convection isn't. By step response do you mean turning the heaters on or inserting the probe with the heaters already on ? Just curious. Did you try to run only the top heaters vs. only the bottom vs both ? Running only the top heaters should null convection. This means that you could achieve a linear ramp using the top heater, then exponential using the bottom one. Peter _______________________________________________ http://www.piclist.com View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist