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Group Head PID??
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Discussions > Espresso > Machines > Group Head PID??  
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cuznvin
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Posted Fri Dec 14, 2012, 9:39am
Subject: Group Head PID??
 

New to all of this and see that the PID dor DB machines have a sensor in the group boiler and one in the steam boiler. Usually the PID is programmed with an offset so that the water is the correct temp for brewinr. This is how I understand it.. Now.. Are there any machines that have a sensor in the grouphead also so that the temp of the brewing water is more accurate?
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frcn
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Posted Fri Dec 14, 2012, 11:03am
Subject: Re: Group Head PID??
 

None that I have seen. The group acts as a heat sink and loses heat to the atmosphere. If the group was at the right temperature at idle, the boiler would be about 5-15 degrees overheated. The temperature control system cannot react fast enough to get the correct temperature of water to the coffee during the brew phase. Not to say that it is impossible, but it would be complicated, and thus, expensive. Some machines have active heating of the group, and others have thermosyphon systems to keep the group close to brew temperature. But controlling boiler temperature using group temperature is another story.

 
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PJK
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Posted Fri Dec 14, 2012, 11:52am
Subject: Re: Group Head PID??
 

I seem to remember a lady who used to post here named Kristy who had a Silvia with a PID controlled boiler and in addition she put a heater (I believe also controlled) in the group head.  How well it worked I don't know.  As I remember she regarded the Silvia a POC and moved to something else.

Phil

 
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cuznvin
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Posted Fri Dec 14, 2012, 12:25pm
Subject: Re: Group Head PID??
 

frcn Said:

None that I have seen. The group acts as a heat sink and loses heat to the atmosphere. If the group was at the right temperature at idle, the boiler would be about 5-15 degrees overheated. The temperature control system cannot react fast enough to get the correct temperature of water to the coffee during the brew phase. Not to say that it is impossible, but it would be complicated, and thus, expensive. Some machines have active heating of the group, and others have thermosyphon systems to keep the group close to brew temperature. But controlling boiler temperature using group temperature is another story.

Posted December 14, 2012 link

Thanks.. So, with your experience, which would be better... active heating of the group or the thermosyphon? I was looking at the Vibiemme DB and it says you need to flush the group for up to 4 seconds if it has been idle for awhile. SO, what would be the difference between flushing an HX machine and flushing a DB machine? If they both need flushing, why not just go with the less expensive HX machine (possibly with a PID)??
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JGG
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Posted Fri Dec 14, 2012, 12:31pm
Subject: Re: Group Head PID??
 

cuznvin Said:

Are there any machines that have a sensor in the grouphead also so that the temp of the brewing water is more accurate?

Posted December 14, 2012 link

Yes, there is at least one ;-)  My home machine has a custom AVR-based board that reads/displays both sensors.

Jim
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cuznvin
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Espresso: La Spaziale Mini Vivaldi II
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Posted Fri Dec 14, 2012, 12:32pm
Subject: Re: Group Head PID??
 

JGG Said:

Yes, there is at least one ;-)  My home machine has a custom AVR-based board that reads/displays both sensors.

Jim

Posted December 14, 2012 link

Nice~!!
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CraigA
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Posted Fri Dec 14, 2012, 12:42pm
Subject: Re: Group Head PID??
 

JGG Said:

Yes, there is at least one ;-)  My home machine has a custom AVR-based board that reads/displays both sensors.

Posted December 14, 2012 link

WoW!, will you post a pic or two of it please Jim?

I'd really like to see that!

 
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ddubick
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Posted Fri Dec 14, 2012, 4:08pm
Subject: Re: Group Head PID??
 

I would also like some more details on your machine as I'm trying to do something similar.  I've got a thread in the mods section discussing my plans.
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JGG
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JGG
Joined: 31 Mar 2006
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Espresso: PID Silvia; PID Alexia
Grinder: Mazzer SJ
Roaster: Hottop D w/HTC+TC4C
Posted Mon Dec 17, 2012, 7:47am
Subject: Re: Group Head PID??
 

I installed this as a prototype a while back, planning to dress it up.  Guess we all know how those things go ;-)

Functionally, it is almost done (user access to PID tuning parameters is lacking).  But as you can tell by the photos, the installation details need some work.  One of these days I may get around to dressing it up, but it is working just fine the way it is.

This particular prototype is built using an Arduino Pro Mini as a daughterboard.  Since this one was built, I've switched over to using a TC4C board (see the open source TC4 project on Googlecode for more info).

Jim

JGG: pid02.jpg
(Click for larger image)
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JGG
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JGG
Joined: 31 Mar 2006
Posts: 1,376
Location: Kentucky, US
Expertise: I like coffee

Espresso: PID Silvia; PID Alexia
Grinder: Mazzer SJ
Roaster: Hottop D w/HTC+TC4C
Posted Mon Dec 17, 2012, 7:50am
Subject: Re: Group Head PID??
 

The innards:

JGG: pid01.jpg
(Click for larger image)
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