Hi Peter,

Apologies for the delay in the response.

Peter L. Peres <plp@actcom.co.il> wrote:
> 
> On Sat, 16 Oct 2004, Sebastian Garcia wrote:
> 
> > Peter L. Peres <plp@actcom.co.il> 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. 


I don't know why you insist with a linear response. Have you obtained a 
cuasi-linear step response data from your oven? 
What are the constructive details it?


> Hmm, maybe an ir oven is linear, but convection isn't. 


I don't think so. 


> By step
> response do you mean turning the heaters on or inserting the probe with
> the heaters already on ? 


Turning the heaters on, with the thermocouple in a center point (air), starting 
from T(amb).


> Just curious. Did you try to run only the top heaters vs. only the bottom 
> vs both ? 


Both heaters running.


> Running only the top heaters should null convection. 


Why? Can you explain this effect? I can't see it.


> This means that you could achieve a linear ramp using the
> top heater, then exponential using the bottom one.


Again, i can't see the explanation of this behaviour.


Regards,

S.-
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