So I tested the PID control of the reflow oven tonight. This was very frustrating, I think I've rectified a few bugs in my code and understand the stepper motor a little more now. One frustration is that if I use 100% speed on the stepper, the quick ramping up of the power in the AC knocks out my serial connection to the pc so I can collect the data but I know the Arduino is still chugging away as the stepper is still adjusting to get the heat curve right.
So another annoyance is that my oven is starting to misbehave in that it is stalling at about 100degrees C before carrying on with the heating and sometime its losing power even though the SCR isn't turned down. Not sure why this is, I think it might have an internal temp sensor in it that is a thermal shut off that is misbehaving. I may have to find out and hard wire in a fix resistance to ensure max power.
I am also thinking that the fan is maybe not really helping at all. I might be best disconnecting the fan leads, removing the metal protector and using a shallower glass bowl that has less volume thus can heat up quicker. In the first part of all my graphs the oven is playing catch up to the curve. Doing this should get the heating element closer to the PCB
anyway The PID is working really well now and I am also thinking of testing it with an clothes Iron like Lebowski has suggested a while back. The beauty of this setup is that I can pretty much plug any heat source into it.
Makes me think about PID for cooling hub motors, that's quite a good application for it really.
https://docs.google.com/spreadsheets/d/ ... sp=sharing
if people are interested here is my current trial runs using the PID logic.