delta76 my first thought was that if it happens after several continuous shots maybe it’s because the pump kicks in and fills the brew boiler with some cold water, which drops the temp. however that does not really make senses because the pump should only kicks in after the shot (they have LSP so kind of weird to ruin that last shot with cold water).
The pump starts during the shot and provides a flow of cold water into the brew boiler to make pressure..It never runs in-between shots to fill the brew boiler.
Looking at the test data the machine at idle was probably at a decreasing state of equilibrium. s they started shortening the idle time, the heating element was activated, then as they continued with the shorter and shorter idle times the heating element got, and retained a big proportional boost. I suspect at and after 4 it was on all the time, especially with cold water entering the top of the boiler and skewing the PIDs view of the temperature.
Thus the machine got hotter and hotter and hotter. This is not real world usage, really only the first two test points are representational and there needs to be a much bigger idle point as well. The PID should be tuned for these and not the continuous production of shots.
