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Group Head PID??
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Discussions > Espresso > Machines > Group Head PID??  
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Stratocaster
Senior Member


Joined: 15 Apr 2011
Posts: 12
Location: Port Elizabrth South Africa
Expertise: Professional

Espresso: Breville 900d
Grinder: San Marco
Vac Pot: No
Drip: No
Roaster: No
Posted Thu Dec 20, 2012, 12:47am
Subject: Re: Group Head PID??
 

Wow Jim, you really seemed to have peaked a lot of interest !. You have obviously done some R & D on the subject of group PID control and I have always thought this is the way to go, so, with a view to not re- inventing the wheel, I have a couple of questions to ask.

1/How do you feel about separate PID control for the boiler and group with perhaps a common reference for control ?, after all, close equalization between the two without interaction between the two PID loops would go a long way to maintaining Temp.

2?Do you think a self tuning PID in the group with the feedback loop  suspended during brewing would work ?

3/ I know this one is flirting with the spectre of loop instability, but how about a master/slave relationship with  the boiler PID maintaining
a minimum differential ?

Just a thought !

Frank
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JGG
Senior Member
JGG
Joined: 31 Mar 2006
Posts: 1,377
Location: Kentucky, US
Expertise: I like coffee

Espresso: PID Silvia; PID Alexia
Grinder: Mazzer SJ
Roaster: Hottop D w/HTC+TC4C
Posted Thu Dec 20, 2012, 12:32pm
Subject: Re: Group Head PID??
 

Stratocaster Said:

1/How do you feel about separate PID control for the boiler and group with perhaps a common reference for control ?, after all, close equalization between the two without interaction between the two PID loops would go a long way to maintaining Temp.

2?Do you think a self tuning PID in the group with the feedback loop  suspended during brewing would work ?

3/ I know this one is flirting with the spectre of loop instability, but how about a master/slave relationship with  the boiler PID maintaining
a minimum differential ?

Posted December 20, 2012 link

My present system does not actively control the grouphead temperature.  Instead, it measures the grouphead temperature and then makes appropriate adjustments to the boiler temperature setpoint.

For instance, my machine can come to virtually flatline grouphead temps within 15 minutes from a cold start.  Normally, this takes around 45 minutes.  But my PID algorithm "knows" that the boiler temperature needs to be temporarily increased until the group is up to operating temperature.  This feature alone (i.e. ready to go after 15 minute warmup) was worth the trouble!

The algorithm does just the opposite when the grouphead is overheated after steaming some milk.  That is, it temporarily lowers the boiler temperature until the grouphead has cooled back down to normal.  So returning to normal brewing temps after steaming is about twice as quick as before.

Jim
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