Finished Pavoni & Fuji PXG4 pid: Probe Inside the Ring
|Delicious cup: all the work was well invested!|
Getting rid of the probe that was fastened with copper tape to the top of the brew group was a priority. I wanted to hide a new probe in the cooling fin as close as possible to the brew group.
This morning I asked Tije if he could do that. He would need to drill a straight hole of 3mm diameter in the 4mm inner ring of the cooling fin that sits as a tight clamp around the brew group.
Always the optimist, Tije set to work:
First, Tije made a piece of aluminum to fit the inside of the ring. Drilling a thin hole straight through the curved aluminum, if possible tangentially going through the inside of the ring to touch the brew head directly, you need the support of the temporary inside piece.
|Aligning the 3mm drill|
|Tije at work|
|You have to look to find the 'hidden' probe|
|Much cleaner sight, just the La Pavoni and the external controller|
Below, you can see the graph of the group temperature probe as the PXG4 is doing its auto-tune to determine the best settings of the internal P, I and D variables. Switching on the heating element for a full minute, the PID traces the delay and proportion of the results, repeats this once more 10 minutes later and then, after another 15 minutes of calculations, it has decided what's the best strategy to keep the group stable as measured from the new vantage point.
During testing with both probes active, I noticed that changes in the room, like a big window opened wide, or me blowing air past the group, change the group temperature, up to a few degrees and if this is a new situation that lasts longer than a few moments, the PID reacts and compensates. I think this is an advantage over PIDs that merely keep the boiler at a specific temperature, especially for a machine with a relatively small brew group as the La Pavoni. I expect that bigger professional brew groups with their much heavier weight keep themselves stable more easily.
I pulled two espresso's. The brew group probe showed a minor blip of two degrees Celsius and the PID guided it back to idle temperature.
Idling, the group temp as seen by the probe is between 77.8ºC and 78.2ºC
I think this La Pavoni PID & P-stat project is finished.
Thanks Wa'il, Tije, Marko and the Fuji team France for your help and suggestions!!
PS added 12 february 2015: I have changed the wiring in the base of the La Pavoni. Now the main switch at the side of the base activates on the heating element power connection that's regulated by the internal pressostat. If I switch that off and I switch on the external PID, then the PID regulates the power to the heating element. I start off the session by switching on the internal P-stat which heats up the machine and group. The group idles around 80ºC and when I switch over to the PID, it keeps the group at 79ºC (I programmed it to be a little hotter than before, yielding more "body" to the shot.)