Plotting the Pavoni Pulse

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(Finished project on
http://kostverlorenvaart.blogspot.nl/2015/01/finished-pavoni-fuji-pxg4-pid-probe.html)

In the previous post I described how a Fuji PXG4 can control the La Pavoni Pro lever machine.

Today I added two extra probes to the free Artisan software so I could simultaneously monitor the temperatures of three essential points indicating the overall behavior and stability of the machine:

1) BT=Boiler Temperature as measured at the bottom of the boiler
2) Brew Group temperature as measured on top of the brew group
3) Coffee Puck, to see at what temperature the espresso is extracted

To connect the two extra probes I used the Amprobe 56 temperature logger.
Setup: Artisan program, PXG4 controller, La Pavoni, Amprobe, books about lichens
Two earlier tests, not documented here, showed me what's the best Boiler Temperature for an extraction around 93ºC. In such things, taste of the espresso and the looks of the crema (not too light, not too dark, the right 'tiger skin' flecks) are decisive and not the 'exact' measurements since probes and loggers have a certain tolerance.

A BT of 120 yielded a scorching hot espresso that touched 99ºC in the puck, so practically boiling temperatures and a BT of 110 got the espresso too light and not hot enough for me. At BT=116ºC this La Pavoni Pro machine worked best as the graphs below will illustrate.

The task (see red line in the graph below) I had set for the PXG4 was to get the boiler at 116ºC in 10 minutes. You can see below that the actual Boiler Temperature joins the target at about 12 minutes.

What I find most fascinating is the behavior of the water between the 7 minute point and the 10 minute point. At 7 minutes, around 70ºC, the water inside the boiler gets more audible, bubbling and softly whistling for a moment even. Air above the water is expanding and softly blowing out of the opened steam wand. The water is heating up faster, the BT line climbing more steeply than before and at the same time the PXG4 needs less power to keep the Rate of Rise it had.

I am not sure what causes the heater in the boiler to be more effective all of a sudden, even with less power driving it. Could it be that not only the air column above the water starts moving out and a little less mass needs to be heated, but also that air that was 'dissolved' in the water is escaping, creating a more dense water mass? See also the more detailed graph further down this page.

Complete graph, annotated (details cut out below)
After 13 minutes, when the BT target has been reached, I do a 30ml flush to warm up the group more quickly. This is effective. After a first espresso I do a brief flush to clean the shower screen but after that the group needs a few minutes to cool down so in the future I'd better just wipe the shower screen clean.

Close up, showing coffee puck probe inside the NAKED portafilter basket
The two extractions that I did came out fairly well but at the side of the basket where the probe was inserted, the probe had wriggled inside the puck as I locked in the portafilter against the group. This could be avoided if I drilled a hole in the bottom of the basket but that would also possibly cause channeling. Now, some first drops appeared below the insertion of the probe and I took some extra time for pre-infusion to get the puck wet and expanded, closing off most of the 'leakage'.

The "NAKED" portafilter in the picture was produced by Gábor from http://www.naked-portafilter.com

Highlighting the interesting behavior around boiling temperature
 Above, I highlight what's happening in the 3 minutes after the BT reaches 70ºC
Top view with used / dry coffee puck

Highlighting group and puck temp around extractions
The extraction of espresso's is fairly stable in temperature, thanks to the Fuji PXG4 and the special La Pavoni Heat Sink built for me by Tije in Amsterdam. The second espresso was slightly warmer, maybe caused by the brief flush but after that second extraction, the group temp returns easily to a temperature close to that before the extraction.

The second cup happened to taste a little better.

The Fuji PXG4 is controlling the machine very well. Since it has no "dead band" the target temperature can be sustained continuously and as such it "wins" from a pressostat but the pressostat does its job at a very low cost, inside a very tiny part with a simple screw to adjust its setting and that simplicity is unbeatable.

I do like the option that the Fuji PXG4 provides to monitor so many details of the 'life' inside the machine, especially when coupled to Artisan and optional extra probes, using the Amprobe 56 or, as an alternative, the more affordable Phidgets.
Espresso and graphs
Related links:

http://kostverlorenvaart.blogspot.nl/2015/01/wiring-la-pavoni-for-fuji-pxg-4.html





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