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jonr
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Joined: 25 Jun 2013
Posts: 256
Location: Americas
Expertise: I like coffee
Posted Fri Aug 9, 2013, 11:05am
Subject: Re: Computer controlled boiler temp - better than PID?
 

> Why would the PID or your board not just add the appropriate amount of heat to keep the boiler at set?

Because they don't know what the boiler water temp is, all they know is what the boiler wall temp is.  Getting one from the other isn't as simple as adding n degrees (unless ambient temp and air flow are fixed).

If I understand him correctly, daduck748 saw a "10-15F drop" in the steady state (pre brew) delta between internal and external probes when he changed the temp of the air surrounding the boiler.  Of course he was adding a preheat coil which changes air flow and radiant effects.  But it does show that what happens outside of the boiler effects the delta between an external probe and water temp.

Thanks for the link.  I agree, fully insulating the boiler should pretty much eliminate this effect and under steady state conditions, make boiler wall temp and boiler water temp about the same.  Might be better than a measurement/software adjustment solution, even if the entire bottom of the Gaggia Classic boiler needs to be left exposed.
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jonr
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Joined: 25 Jun 2013
Posts: 256
Location: Americas
Expertise: I like coffee
Posted Fri Aug 9, 2013, 11:34am
Subject: Re: Computer controlled boiler temp - better than PID
 

Today I modified the preheat and brew code to allow a hybrid of open and closed loop techniques.  You can control brew heat to temperatures (realizing that what it sees is delayed and offset in unknown ways) or to PWM values (open loop, similar to rapid temp surfing).  The table is still there - so instead of trying to control to a single value (like a PID alarm function or dual PIDs would do), you get to specify a different value for each second of the preheat and brew cycle.   Ie, the goal was to allow more frequent and more accurately timed switch flips than manual temp surfing could ever do and allow a more flexible form of the control that PID during brew does.  It's up to the user, depending on the values they put in the table.
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D4F
Senior Member


Joined: 15 Mar 2012
Posts: 1,878
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Preciso
Posted Fri Aug 9, 2013, 8:00pm
Subject: Re: Computer controlled boiler temp - better than PID?
 

jonr Said:

I suspect that ambient temp is why people let machines warm up for so long.  The Gaggia Classic has enough heater power to bring the boiler from room temperature to desired temp in < 2 min.   So why 20 min warm ups?  At 2 min, the air around the boiler is still pretty cool and significantly effects the boiler wall temperature reading.  Ie, there is a different temp offset between the boiler wall and the water - and a few degree error in water temp impacts coffee taste.  If it could be made to work well, a 2-5 min warmup would be of some convenience value to me.

Posted August 8, 2013 link

Those heaters are in the boiler wall, so some time has to be given for water temperature to stabilize, and the group and PF.  Are you going to actively heat the group and PF?  You could use water flush as Andy did but then you are again waiting to stabilize.

 
D4F also at
http://www.gaggiausersgroup.com/
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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 256
Location: Americas
Expertise: I like coffee
Posted Fri Aug 9, 2013, 8:36pm
Subject: Re: Computer controlled boiler temp - better than PID?
 

My guess is that 2 min to heat up (probably by initially overheating the walls to some extent) and then 2-3 min to distribute that heat evenly is enough.   An internal probe would be the way to find out.

Are there easy ways to put in an internal probe?
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jonr
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Joined: 25 Jun 2013
Posts: 256
Location: Americas
Expertise: I like coffee
Posted Sat Aug 10, 2013, 7:26am
Subject: Re: Computer controlled boiler temp - better than PID?
 

It looks like 2 minutes of steam temp (overheat) and then 8 seconds of flush (cool down and group heat) brings a cold Gaggia up to brew temp very quickly.  It would take some further testing to get the exact right times.
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D4F
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Joined: 15 Mar 2012
Posts: 1,878
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Preciso
Posted Sat Aug 10, 2013, 9:16am
Subject: Re: Computer controlled boiler temp - better than PID?
 

I believe that Andy could do that in 5 minutes, perhaps less.  Problem is, it is not automated and requires user input and time, and the inherent inconsistency.  You might automate that on your board?  Many ideas can be done, but are they a practical and economical help for the home user?

 
D4F also at
http://www.gaggiausersgroup.com/
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jonr
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Joined: 25 Jun 2013
Posts: 256
Location: Americas
Expertise: I like coffee
Posted Sat Aug 10, 2013, 2:27pm
Subject: Re: Computer controlled boiler temp - better than PID?
 

I agree, it's rare that I really need a 5 min warmup.  But I'm sure that most of it could be automated with the computer.  Probably would need a LED to flash or something to indicate when and how much water to flush (or maybe the flush could be eliminated) and another LED for when it is ready.

At this point, I'm mostly concerned about how to tune things.  It's going to take a lot of trials and tasting to determine the exact temperature profile I want throughout brew.  Being able to control it is only the beginning.
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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 256
Location: Americas
Expertise: I like coffee
Posted Sun Aug 11, 2013, 8:44am
Subject: Re: Computer controlled boiler temp - better than PID?
 

Here is an interesting article that talks about a flat brew temp profile not being ideal.   I wonder where "flat is ideal" came from?   Also, flat above the coffee means very non-flat within the coffee (which is what really matters).

It also talks about  .1 degree making a difference in taste (but I think that to get actually bad espresso, you need much more error than that).

Click Here (www.espressotec.com)

Also:

Click Here (www.caffeculture.com) (4C drop is better, 1 degree matters)


I'm trying for a 94C to 91C dropping profile to start with.  Even guessing at values, I'm already getting amazing good taste.
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andys
Senior Member
andys
Joined: 10 May 2003
Posts: 813
Location: NY
Expertise: Just starting

Espresso: Speedster, Londinium 1
Grinder: EK-43,Robur, HG One, M3
Vac Pot: Yama
Drip: various
Roaster: PIDed Popper
Posted Sun Aug 11, 2013, 9:48am
Subject: Re: Computer controlled boiler temp - better than PID?
 

jonr Said:

Here is an interesting article that talks about a flat brew temp profile not being ideal.   I wonder where "flat is ideal" came from?

Posted August 11, 2013 link

As others have said, the "flat temperature profile" concept came over a decade ago from David Schomer. Few knowledgeable people in the specialty coffee industry still buy his claim, however.

Also, one doesn't need a fancy control system (Rancilio or homemade) to experiment with declining temperature profiles. Try a lever machine or a heat-exchanger pump machine; many of these provide a declining temperature profile through their physical design.

 
-AndyS
picture page:  http://flickr.com/photos/andy_s/sets/
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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 256
Location: Americas
Expertise: I like coffee
Posted Sun Aug 11, 2013, 10:01am
Subject: Re: Computer controlled boiler temp - better than PID?
 

My experience with HX was that while it did naturally have a drop during brew, the starting brew temp was so effected by flush, incoming water temp, flow rate and ambient temp that I had no interest in keeping it.  For me, a low cost Gaggia Classic plus $30 worth of controls is producing much better results.

A small boiler machine also has a natural temp drop.  In the case of the Classic, it's excessive unless you reduce it by bumping up boiler wall temp just before or during brew.
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