Time to PID a Pavoni

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


Several models of espresso machines have a PID on board these days. As far as I know, all of these are used as mere thermostats, making sure the boiler (and sometimes a second boiler) is kept at the right designated temperature, and since temperature and pressure go hand in hand inside a boiler, also the correct pressure.

For a brew boiler, the temperature is most important even though the pre-infusion pressure is relevant as well in a lever machine. For a steam boiler, the pressure is most important to be able to steam that milk to a creamy froth. Still, these values, pressure and temperature, cannot be seen separately.

A problem for most PID devices is that it's HOT inside an espresso machine, around 50ºC and the PIDs are mostly designed to survive in an environment of 60ºC maximum. The result is that such a PID inside often has a limited lifetime.

On the current Rocket espresso machines the PID is placed as low as possible in the housing of the machine, hidden behind the drip tray, where the heat is less of a problem and where room temperature air is flowing past it, up into the body of the machine. One additional advantage is that the "digital" looks of the PID does not ruin the classic design of the machine front.

A PID can be very convenient in the smallest semi-automatic espresso machines like the Rancilio Silvia.

Some have already built a simple PID in a La Pavoni as well, as you can see with a quick search on YouTube. One user, Ray, finished such a project in 2011 and he has recently decided to sell that machine for $2,500.=

Still, I haven't yet seen anyone fitting an espresso machine with a fully programmable PID that can also be programmed and monitored on a computer and an iPhone. So I set out to build one, copying most of the hardware and settings from my earlier build of a roast controller, based on the highly configurable Fuji PXG4 controller.

Fuji PXG4 controller on the left, red Amprobe for group temp, iPhone monitor, La Pavoni and Artisan on the laptop
One thing that I learned from the first two tests, warming up the La Pavoni and making an espresso, is that it makes a big difference that this little machine has no anti-vac.

As the heater is on full power after the first minute, and the water inside the boiler warms up, the air above the water column also heats up and expands. This "false pressure" cannot escape as it does during warm up in most larger espresso machines and the heating element struggles to get the temperature and 'real' water/steam pressure up.

You can see this in the illustrations below.

Released steam/air after 10 minutes, then the water warmed up faster
The dark line that climbs up immediately at the start is the heater which is gradually turned up to full capacity in the first minute. The red line is the target temperature which is reached at 13 minutes. The PXG4 already gradually turns down the heater after 11 minutes in anticipation of the water inside the boiler reaching its final temperature level. A more primitive PID might allow the element to work harder, then overshooting the target and subsequently meander around the actual target temperature.

Having the PXG4 "get the feel" of the La Pavoni during a short "auto tune" session does help and also switching on the optional "fuzzy logic" of the PXG4 instantly makes the controller very effective. No need to tweak and search for the optimal settings of the P, I and D variables.

What intrigued me was how much easier the heater could do its job after I had released the excess of expanded air after 10 minutes. Until then, the heater had been on full blast and all of a sudden it had a much easier life.

This could be a reason to build an anti-vac on the La Pavoni or at least make it a habit to keep the steam valve open and stay around the machine to close it once hot water and steam begin to come out of the steam wand.

In the example below, I did just that, keeping the steam valve open until it started to spit hot wetness:

Kept steam valve opened until steam / hot water spat out at about 9:30
In both cases, the bottom of the boiler reached the boiling point of 100ºC at about 10 minutes.

Interestingly, after 9 minutes in the second example with the steam wand open, starting at 80ºC when the boiler water began to audibly "sing", the PXG4 temporarily lowered the heater load and at the same time the heater was more effective. I closed the steam valve around 9:30 and the PXG4 kept the element at full capacity again, lowering that gradually after 12:30 to make sure the temperature landed and stayed exactly at the new target temperature that I had selected.

Another thing that strikes me: once the boiler is hot enough, the element has very little work to do, around 20-30% of capacity, in short spurts of a few seconds at a time. Having a 1000W espresso machine does not mean you are spending much money on a machine burning a kilowatt continuously. It's mostly idling away at a low capacity.

Now it has become very easy to figure out what temperature I like best for my cup from this little machine.

I have added a second probe to the group so I can monitor what (if any) constant difference there is between the temperature at the bottom of the boiler and the temperature on the top of the brew group, comparing this to the heat sensation when drinking an espresso, and looking at the color of the extraction. The crema should be darkly mottled but not too dark as if burnt.

Anyway, next time I need to go on a short vacation I plan to take this new expanded setup with me so I can safely ignore the tourist destinations near my hotel and enjoy the bliss of my own delicious brew!

Not forgetting this is in the end all about the joy in the cup!
As always, thanks Marko Luther for the free Artisan software, Wa'il al-Wohaibi for your advice, and the staff at FUJI for your assistance. And Tije for customizing the aluminum box!

Related links:

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











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