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Nice! Interested in your data. I've heard of people turning off the machine and wrapping a wet cloth around the group to prevent the temperature rising too high with multiple shots, which seems a bit, rudimentary.
Normally not an issue for me as I'm normally just making 2 at a time, but it's good to see some proper data about the issue.
mmccarthy-
I only make one cup per day, as I'm a recovering caffeine addict myself and my other halve doesn't drink coffee at all. So I'm afraid I won't be able to comment on its characteristics when pulling multiple shots. But I will probably be buying some cheap coffee this or next weekend to experiment with temperatures, so I'll try to see what shots in quick succession are like.
It seems the PID values are roughly where they should be. In this chart I'm still running it off the pressostat, but I'm also running the PID parallel.
- the blue line is the input (temperature)
- red line is the heater output (I run it full gas until 15 degrees below the setpoint, only then does the PID kick in)
- black line is the setpoint (roughly as I added it in Photoshop).
- the blue line is the input (temperature)
Tijmen
Logging some data with the Pavoni still running off the pressostat shows that this is worthwhile upgrade. A nearly 15 degree difference between the lowest and highest temperature. (Temperature in celsius and time in minutes, to be clear. Sorry for my sub-par axis labelling.)