Let's Make Robots!

Reflow Oven Fan Modified == Good PID loop \0/

16 May 2011

Today I made a slight modification to the toaster oven to see if I can improve the PID loop response.  I was having issues with oscillations no matter how much I adjusted the PID gains.  I suspected this was because I turned the oven on/off in response to the PID output.  This meant the internal oven fan pulled the temperature down below the setpoint a bit every time the oven was turned back on again.  Another side affect is the temperature would overshoot the setpoint a bit once the PID attempted to compensate for the undershoot.

A simple fix was to separate control of the internal oven fan from the control of the heating elements.  Now, the fan is turned on at the beginning of the process and turned off once the cool down phase is complete.  The result is a much more stable PID loop that does not over or undershoot the setpoint by more or less than 2 degrees.  Proof is in the pudding so take a look at the included chart.

Exported chart in Excel

Exported chart image as captured by Reflow Oven Controller application

I have a few more changes/additions to the software application and some documentation to take care of.  I'll post all of the files as soon as that is complete and I have a reflowed PCB to show off. \0/