corey Senior Member Joined: 26 Sep 2003 Posts: 1,148 Location: Perth, Australia Expertise: Professional
Espresso: Synesso, Marzocco Grinder: Mazzer Robur
Posted Fri Dec 31, 2004, 2:57am Subject: Re: Naked PID'ed La Marzocco Xmas present
Hey Simon, yeah I'll keep you updated on my development. The amazing thing is I thought it would operate exactly the same as my 3 group at work but it performs entirely differently. Got a couple of LM triple baskets on the way from CoffeeParts, should be pretty awesome. Hey Gregor, there is a reasonable amount of space between the Mazzer and the LM, I guess I would like more but you know how it is. You can't have a mazzer and a La Marzocco and a PID and a naked PF and room for drinks, somethin's gotta give :)
Posted Fri Jan 7, 2005, 12:28pm Subject: Re: Naked PID'ed La Marzocco Xmas present
corey Said:
The other issue is that the PID cycles through temps of 92-98 degrees C as it cools down and heats up, which basically means that it all depends on where in the heat up/ cool down cycle you pull the shot.
Hey Corey, I'm a bit confused by this statement. I thought the entire point of PID was to avoid having temperature swings such as this, especially a 6 degree C swing, which IMHO, is huge. I realize my PID'd Silvia is a completely different animal, but the only time I would see a swing like this is when I hit the brew switch, and cold water starts being pumped in to the boiler. The overshoot when reheating is never more than 2 degrees F, which then settles back down to my set temp of 223.5 in a couple minutes or less. I'm sure I am just misunderstanding the situation in some way.
Chris
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corey Senior Member Joined: 26 Sep 2003 Posts: 1,148 Location: Perth, Australia Expertise: Professional
Espresso: Synesso, Marzocco Grinder: Mazzer Robur
Posted Fri Jan 7, 2005, 6:01pm Subject: Re: Naked PID'ed La Marzocco Xmas present
Hey mate, to answer your question, the PID is set for a target temp of 94 C with a band to swing between 93-95 C. Basically the heating element will come on at lower than 93 C and then heats and stops heating once it hits 95 C. Because the heating element still contains heat (although it has switched off) the temp will continue to rise until it stops at about 97-98 C then it slowly cools to rest at 94 C then cools off and begins the whole process again. Depending on how much water is let out of the group, the heating element can come on at full power if the machine has been forced too low or partial power if the temp is close to its set temp already. I have heard of some PID's that will cycle a little faster but this is how the standard stock LM PID seems to function. I would love to have better control over my brewing temp but that might take some more research and tweaking. Maybe I could try and adjust the band to be set at 94 C both its high limit and low limit and see if this changes anything.
Posted Fri Jan 7, 2005, 6:29pm Subject: Re: Naked PID'ed La Marzocco Xmas present
Ahh, ok... It has to do with how the PID's are set up on the Marzocco's. Yes, you should be able to get (much) better performance than that. For instance, on the Silvia when I first turn it on from dead cold, the heating element comes on full (steady element light). As it approaches set point my set point of 223.5 F (when it hits 190 F it begins to "blip" the heating element in half second intervals. In this way it minimizes overshoot. For instance, from a cold start, my overshoot was 0.7 of a degree farenheit. The highest temp I saw was 224.2 F, and then it settled back to within a couple couple tenths of 223.5 F. Because of the curiosities of Silvia's plumbing, this temp gives me 201 F in the portafilter, every time I want to pull a shot. Not across the entire shot, because the boiler is too small, but it does a pretty good job each time. It is VERY easy to tell a 2 degree F difference on the set point of the PID in the cup. I'm guessing that Marzocco has a reason for the way theirs are set up, perhaps it is preferable for a commercial environment. Honestly I have no idea. All I do know is that you should be able to have it set up in such a way that every time you hit the button to brew, you should be able to get the same temp in the portafilter.
Chris
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fad Senior Member Joined: 19 Apr 2003 Posts: 633 Location: Sydney, Australia Expertise: I live coffee
Espresso: Grimac La Uno, Isomac... Grinder: Mazzer SJ. Cunill... Vac Pot: Bodum Santos Drip: SwissGold Roaster: Ron Kyle BBQ Drum,...
Posted Fri Jan 7, 2005, 7:10pm Subject: Re: Naked PID'ed La Marzocco Xmas present
corey Said:
Hey mate, to answer your question, the PID is set for a target temp of 94 C with a band to swing between 93-95 C. Basically the heating element will come on at lower than 93 C and then heats and stops heating once it hits 95 C. Because the heating element still contains heat (although it has switched off) the temp will continue to rise until it stops at about 97-98 C then it slowly cools to rest at 94 C then cools off and begins the whole process again.
Hazel @ Coffee Alchemy has the same symptoms with her Linea. I've been reading up on the ERO PID unit that they use and have come to suspect that the PID unit isn't being used as a PID, but a fancy high-priced electronic pressurestat.
The ERO, like most of the temperature controlers out there, can act like a pressurestat: turn on at X degrees and off at Y. This will give the deadband you're experiencing.
If you give the unit the right parameters it turns on the P, I and D equations and should have a deadband that's a lot lower. With a stable system 1 degree changes are possible. 0.1 degrees or less in a lab environment.
According to alt.coffee regulars like Barry Jarret & Andy Schecter one problem with the stability on the Linea is the cold water topup, which sends the temperature out of whack. They've done mods where the water is pre-heated before the boiler, and that makes a big difference.
Depending on how much water is let out of the group, the heating element can come on at full power if the machine has been forced too low or partial power if the temp is close to its set temp already. I have heard of some PID's that will cycle a little faster but this is how the standard stock LM PID seems to function.
It's all in the settings, and the stock settings seem to suck ;)
We'll see what the LM tweakers recommend, and post the results.
corey Senior Member Joined: 26 Sep 2003 Posts: 1,148 Location: Perth, Australia Expertise: Professional
Espresso: Synesso, Marzocco Grinder: Mazzer Robur
Posted Sat Jan 8, 2005, 5:49pm Subject: Re: Naked PID'ed La Marzocco Xmas present
Hey Paul, after alt coffeeing a little it seems that Barry and Andy set up their LM's by having the water input to the brew boiler being pre-heated by wrapping the water input copper piping inside (or outside) the brew boiler first. They also recommend lengthening the banjo tube (I don't even know what the banjo tube is, by the way), Schomer also does this. I suspect that you are right that the stock LM PID is set up as an electronic thermostat rather than a true PID. I wonder if I re-programmed the stock PID, if I could still get improved results anyway. Just one problem, how the hell do you re-programme it?
Corey (really need to get myself an electronics degree) Diamond
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