Re: gEDA-user: reflow oven

[Bill Sloman <bill.sloman@xxxxxxxxx>]

At 19:14 7-5-2006, you wrote:
> 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 
> subtracted 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.

This is proportional-derivative control 
implemented by someone who hasn't heard of 
proportional-integral-derivative (PID) control. 
Google for an absolute flood of information.

http://lorien.ncl.ac.uk/ming/pid/PID.pdf

It is a technique that has been around for a 
while - the Ziegler-Nichols tuning technique for 
PID controllers refers to the paper they published in 1942.

--
Bill Sloman, Nijmegen