> I'm also curious to know how the controller can control pressure with the vibe pump
Regular control loop with feedback: Pressure sensor measures pressure, controller adjusts pump power, nearly stepless via phase angle control circuit (pump sounds more or less normal with this type of control). How exactly it is adjusted must be configured by the user, like a PID controller for temperature must be configured by the user. Details in the leva! manual at projectcaffe.bplaced.net/beta.html
Have you already gone through the pressure profiling setup tutorial in the leva! manual? I'm asking because a screenshot in #4 shows that 7.9bar were achieved while 9bar were programmed. That is not normal. The error should be a fraction of a bar, like here: http://www.vimeo.com/301475180
. Since the yellow plot of the pump power was not turned on, I can not tell if that happened because the grind was so mismatched that even full power couldn't get the pressure to 9bar (one has to grind finer after introducing preinfusion) or if the pressure profiling needs tuning. Factory defaults will not work, except by luck.
> sure you are allowed to install the pressure sensor running with hot water?
Rated for 125°C. What has to be avoided is vibrations. Installation directly at the pump would be a no-go, even if it would be much cooler.
> discusses it a little in the "Alternative to PID" chat.
That was here: Alternative for PID
> Pressure/flow profiling works via vibe pump since 2016 or so
The leva! firmware is not a new development. It is a relabeled caffe! firmware. caffè! has been around for ages. First released for faustino 1 modules, produced ca. April 2009.
> over-pressure ... valve ... sends water back ... If the flow rate is measured before the bypass valve, then it could be biased high
Ideally, an over pressure valve would be set to a pressure that won't interfere with pressure profiling but still provide the safety function. For example, it could be set to open slightly above 9 bar if the preferred maximum brew pressure is 9bar. At such a setting, it would not cause flow meter measurement errors.
But even then, a flow meter between tank and pump (measuring water) can not give meaningful values if one is interested in the flow rate of the coffee - because it will measure a lot of water that will never exit the machine as coffee:
- Water that fills tubes and air pockets (in boiler and filter)
- Water that gets soaked up by the coffee.
Such flow meters have limited use for dosing, let alone flow control. They have other uses, for example improved temperature control by instantaneous flow-driven reaction a.k.a. "feed forward control".