by Mole : 13th July 2008
updated : 4th October 2008
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Issue: The Izzo Alex Duetto PID settings are too aggressive, causing overshoots on the brew boiler temperature, or simply not matching your coffee making routine.
Solution: Re-program the PID controller with more conservative settings to match your environment and routine.
For more information, read on…
PID Controller Profiles for the Duetto
For those interested mainly in what settings they should use, and less interested in self-tuning, or wanting a basis to work from, here are some easy-set profiles which I believe will give good results… For instructions on how to program the PID controller in the Duetto with one of these profiles continue on to the next section.
The European Variant
The following profiles have been developed on my personal machine, which is a European variant of the Duetto running on 240V. The European model has a 1kW brew boiler element and (approximately) 1.4kW steam boiler element and utilises a 1C increment PID temperature controller. The machine is normally set to around 93C in an ambient temperature of about 20C and has a temperature offset of 10C. My steam boiler pressure is about 1.4bar top of cycle1. Remember that the machine must be on for at least an hour before tuning and that all machines could have minor differences: depending on what brew temperatures you test at (e.g. extremes of, say, 88C or 97C), the steam pressure you run at and the offset you use, your results could be slightly different.
In particular, if your ambient temperature is particularly lower or higher than 20C or your supply voltage is significantly less than 240V you may need to tweak your chosen profile for your own situation. For example, when running at 220V you may need a slightly higher Proportional gain (P) and/or Derivative gain (D) from those in the table below. Also, insulating your brew boiler will almost certainly require the parameters to be lowered somewhat, but I have no information yet as to how far! (click here to read rest of article)