Re: gEDA-user: reflow oven

[Stefan Dröge <gecko4ever@xxxxxx>]

Levente schrieb:
> I use a PT100 sensor. If you have any idea on how to mount the sensore to reduce the "inertia"...please share. Currently it's mounted on a piece of PCB.

In the german "Elektor" magazine was a report how to build a Reflow-Oven 
from those "Mini-Pizza-Ovens" like this one: 
http://ec1.images-amazon.com/images/P/B0009RLDZ0.03._SCLZZZZZZZ_.jpg

They used a AT89C52.

They calculated the inertia "out".
Thats how they made it:
First they measured the steepness of the temperatur-rise from 50°C-100°C.
When the temperature reaches 100°C the heating is turned off. Then the 
temperature increases a few degrees (like it can be seen in your 
diagram). This is also measured (They called it "Overshoot")
Then the overshoot is divided by the steepness we measured before, and 
saved as a constant in the µC (I will call it coefficientT, they called 
it also Overshoot what is a little confusing).

The µC measures in operating mode every second the current steepness of 
the temperature-rise. This is multiplied with "coefficientT". Now you 
get the "guessed" overshoot. This value is substractet from your 
destination temperature. Now the heating is turned off (or whatever) a 
little bit earlier, and you reach your destination temperatur very 
exactly. They specified a deviation of 1°C.

Link to the project description (you can download the PCB and the 
Sourcecode for the µC):
http://www.elektor.de/Default.aspx?tabid=28&year=2006&month=1&art=5550657

Some german words:

"Platine" is german for "PCB".
"gratis" = "free of charge".



Then I have another (german) site for you: 
thomaspfeifer.net/backofen_smd_reflow.htm

He used a 1N4148 diode for temperature measuring, and a AT-Mega8.
Here is a site where he describes the it more detailed (ok, this won't 
be useful for you because its german, but there is a image of the 1N4148 
temperatur-curve): 
http://thomaspfeifer.net/laminator_temperatur_regelung.htm

Sorry for my spelling :-)

Stefan



P.S: To the german-speaking-users in this Mailing list: Was heißt 
Temperaturgang auf englisch?