cafeIKE wrote:1st-Line claims, but has not supported, that a slight amount of scale drastically affects PID performance.

Sorry, but on that one... Yuh know - we tend to always look to scale when something goes wrong, and occasionally it is, but often the prob is on the other end of the pf handle...

Getting back to my original issue of the temp being 2 degrees F different than the PID setting: is there an adjustment that can or should be made in the advanced PID settings?

Yeah, your thread got hijacked! Sorry!

For the Fuji, in the second parameter bank, there is a Process Value Offset PVOF (PUOF) where you can put that kind of offset you wish.

I do not know what brand PID QM used in the Silvano, but I bet Chris would know and would be able to help you get an answer to your question.

I just stopped and viewed the Vimeo video on the Silvano on Chris' site - I gotta say, those videos are the greatest thing since sliced bread! Love 'em! VERY smart move on Chris' part. But then I noticed that he has craftily placed a link to the Silvano PDF manual, so I looked at it and at page 9 it tells you how to change 5 very critical parameters. Perhaps the bottom parameter would do what you wish.

FYI, from the manual, the PID is a GICAR with the same parameters as the latest Brewtus, Duetto and DoubleDomo. It's a good unit.

innermusic wrote:Getting back to my original issue of the temp being 2 degrees F different than the PID setting: is there an adjustment that can or should be made in the advanced PID settings?

If the display does not change if the machine is left to idle for a couple of hours, then changes ONLY after a shot is pulled and never returns to the set point after a couple of more hours AND the environmental conditions remain constant, contact the vendor as this is not what a PID is supposed to do. I'd expect the temperature to return almost immediately, surely within a couple minutes at most.

If you decide to contact the vendor make a complete list of your exact procedure.

innermusic wrote:Getting back to my original issue of the temp being 2 degrees F different than the PID setting: is there an adjustment that can or should be made in the advanced PID settings?

You are seeing a temperature difference from what the PID reads to the temperature of the water coming out of the grouphead? If so this is normal and would be attributed to various metal parts stealing heat from the water on its travels from the boiler to and through the portafilter. If this is the case just adjust the temp on the PID to accommodate the heat loss.

I hope this comes across well as my first post on H-B. I recently purchased a Vibiemme DoubleDomo v2. I'm an EE with substantial training (but little commercial experience) in control systems and PID. I think this has been covered somewhat in previous discussions but it seems relevant to this discussion.

If you look at the Wikipedia page on PID controls, you will see that there is always a balance between how fast a PID controlled system reaches the setpoint and how long it takes to reach that temperature. See http://en.wikipedia.org/wiki/PID_controller where the pictures show this fairly clearly. That page also gives some examples of the impact on changes to each of the values for P, I, and D.

I've noticed that the temperature on my Vibiemme does sometimes go above the setpoint, especially right after pulling a shot. I think that this is typical control-system overshoot. It might be what you are observing in your machine.

You can tune the PID values for faster post-shot recovery times if you don't mind oscillation or overshoot. If you really don't want overshoot, you can choose slower recovery that never goes above the setpoint. It's hard to know the scale of the PID values for a given controller or what models the dynamics of the specific boiler and heater most closely but eliminating overshoot is probably the most straightforward thing you can do in tuning a PID as long as you accept that you won't have the fastest recovery your machine is capable of.

Hope this helps.

Pizzaman: Is that overshoot the result of the PID only controlling the heating element and not having any control over cooling? Could the controller be set up to do something (dump boiler water and add some fresh cold water) to keep the temp exact? Whats a few more valves, wires and programming?
PS: What about using a pressure transducer instead of a thermocouple? They are available in the proper pressure range and temperature working range. 4-20mill loop?

You are right, the PID only has control of the heater. For temperature control of boilers, this is frequently the only controllable variable.

In a more sophisticated system (read as more expensive) there might also be other controllable variables. In theory, an espresso controller could allow inflow of unheated water to cool the contents of the boiler. If the inflow temperature was measured and the volume controlled by a positive displacement pump, cooling could be controlled. I'm making very liberal use of my "in theory" caveat! As you mention, it would be extra piping, valves, more sensors, and a more sophisticated controller. More importantly, it would take much more in-depth modeling and programming to make it work well.

In practice, I don't think automatically controlling the cooling is necessary. The is usually inflow of cool water whenever water flows out the group-head. In addition, the only incoming heat is typically the boiler's heating element so controlling that can keep excess heat from entering the boiler.

The newer-design double boiler espresso machines use a heat-exchanger in the steam boiler to preheat the water going into the brew boiler. This results in smaller temperature difference between the incoming water temperature and the boiler set-point temperature. This means that smaller amounts of heat will have to be added and overshoot will be smaller (as long as the PID can give out heat in small enough increments which is likely). The Duetto and DoubleDomo v3 work this way and I think the Brewtus does, as well. Note that my v2 does not.

Warrior372 wrote:You are seeing a temperature difference from what the PID reads to the temperature of the water coming out of the grouphead? If so this is normal and would be attributed to various metal parts stealing heat from the water on its travels from the boiler to and through the portafilter. If this is the case just adjust the temp on the PID to accommodate the heat loss.

The problem is not an overshoot after pulling a shot. I don't mind an slight overshoot so long as the temp then falls to the setpoint. Problem is, after the overshoot it then falls BELOW the setpoint and remains 1-2 degrees F below it.

Speaking in generalities, the PID algorithm relies on integral action to zero out persistent droop below setpoint or hovering above setpoint. Increasing the integral gain should help, particularly with the droop.

I notice in the manual that the default tuning for Fahrenheit operation has zero integral gain. I might try bumping this up in increments of 0.05. I'm not sure I understand why the Celsius tuning would include I, but not the Fahrenheit.

Almost a year ago, Chris sent me a Silvano for temperature tests. The PID tuning on my test unit was so good that I told him I didn't think I could improve it. This seems at odds with your experience, though.

Jim