Author Topic: Measuring temperature in the boiler  (Read 2809 times)

Offline The Big L

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Measuring temperature in the boiler
« on: January 28, 2014, 08:03:25 AM »
Suppose someone wanted to use something like this to measure the temperature of the water in the boiler on a Classic: DB18B20 temperature sensor probe

Then how would we get the sensor into the boiler?  Could something like this be made to work with the Gaggia Classic?  If not, how else might one get that 1/4" stainless probe into the boiler?

Offline val

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Re: Measuring temperature in the boiler
« Reply #1 on: January 28, 2014, 08:26:00 AM »
On the KA Proline, the thermometer for the brew boiler goes inside a thermo well in order to reach the water temperature. see picture.
For testing purposes you could disable the steam feature and test the temperature, i think pizzaman83 brother installed something like that on a gaggia espresso.

Offline SusanJoM

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Re: Measuring temperature in the boiler
« Reply #2 on: January 28, 2014, 09:51:54 AM »
The Old Old Old Orange Baby has a similar well in the boiler for inserting a temp probe.   I had forgotten about that.  I don't think the Espresso is so equipped, however;  the boilers had been redesigned by the time the Espresso started being built.
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Offline D4F

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Re: Measuring temperature in the boiler
« Reply #3 on: January 28, 2014, 11:40:23 AM »
Daduck made a fitting and probe and describes some findings.

http://coffeegeek.com/forums/espresso/machinemods/609878?Page=2

It is a fairly simple fitting that seals with the steam valve O ring, but the steam valve was gone.  Perhaps both can fit in the same spot concentrically. 

What is that advantage and disadvantage of boiler water temperature?  It is not simple to get that temperature and that temperature has some variation with height in the boiler.  In fact, boiler temperature stratification is the reason the Gaggia works. Hot at top and the cool water enters the bottom, thus the central stand pipe.

Boiler water suffers the same problems as the boiler, rapid changes.  The boiler gets very rapid heating with the element encased and the boiler water changes temperature rapidly with incoming.  In the end both have an offset of temperature at the puck/brew head.

Does temperature in the boiler water matter any more than temperature of the boiler, just a different offset.  What helps is a thermometer and known temperature and thermofilter at the group to help determine the offset.  Of course you can find enough references to just use the known or stated offsets and your taste to produce the cup you want.  You can also get there by trial and error and experience without a thermometer if you are very patient and persistent as all of us are :)   Not  :)

Offline pizzaman383

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Re: Measuring temperature in the boiler
« Reply #4 on: January 29, 2014, 06:36:25 PM »
What is that advantage and disadvantage of boiler water temperature?  It is not simple to get that temperature and that temperature has some variation with height in the boiler.  In fact, boiler temperature stratification is the reason the Gaggia works. Hot at top and the cool water enters the bottom, thus the central stand pipe.

My brother and I are using the KA thermo-well to permit measurements of the boiler water temperature.  Your comment about temperature stratification is accurate but our experience seems to show that measuring the temperature near the level of the top of the central stand pipe promotes more consistent temperature control.  We think this is because the PID controller sees the difference between applying heat and it effecting the temperature measurement at the same time as when the water temperature actually changes.

Offline The Big L

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Re: Measuring temperature in the boiler
« Reply #5 on: January 29, 2014, 08:32:07 PM »
D4F - I just wanted to thank you for your thoughtful input on this thread (and others).  I've read many of your posts here and on CG, and I've learned a lot from your experience and even your thinking aloud.

pizzaman - I was thinking about that earlier.  Because the water at the bottom of the boiler starts changing so fast when new water is introduced, and because the temperature at the bottom quickly becomes quite different than the brew temperature (hopefully!), I'd think that a PID would have trouble dealing with the lag in an appropriate way.  Temp measurements near the top make good sense to me -- or perhaps just a little further down, which would give the PID a slight head start when the temperature starts changing rapidly during the brew.

Offline SusanJoM

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Re: Measuring temperature in the boiler
« Reply #6 on: January 29, 2014, 08:39:26 PM »
Just as an aside, I don't think anyone expects a PID to have any impact on the intra-shot temperature of a Gaggia. 

The PID is only expected to give a repeatable temperature at which to start the shot.

“Not everything that can be counted counts, and not everything that counts can be counted.”
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Offline The Big L

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Re: Measuring temperature in the boiler
« Reply #7 on: January 29, 2014, 10:02:54 PM »
Just as an aside, I don't think anyone expects a PID to have any impact on the intra-shot temperature of a Gaggia. 

The PID is only expected to give a repeatable temperature at which to start the shot.

I don't really understand this statement.  The whole point of the PID is to try to keep the temperature as close to a set point as possible.  Granted, this job is much easier for a PID algorithm when the system is at a fairly steady state (warmed up and idling).  And sure, I can understand that tuning the PID parameters to keep the brew temp (or some proxy, whether it be water-in-the-boiler temp or boiler wall temp) in range could be difficult given the small size of the boiler and the fast-heating element.  Difficult, and imperfect, but not beyond all hope.

Offline SusanJoM

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Re: Measuring temperature in the boiler
« Reply #8 on: January 29, 2014, 10:17:45 PM »
I think if  you read everything you can about PIDs and Gaggias with their miniscule boiler capacity, you will discover that what I have said is the sad truth. 

Playing with a thermofilter and watching the intrashot temperatures of my PID'd Classic indicated a definite drop in temp during the shot, although not as dramatic as the findings of others when conducting similar tests. 

Sorry
Susan
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Offline The Big L

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Re: Measuring temperature in the boiler
« Reply #9 on: January 29, 2014, 11:13:29 PM »
Actually, I think all my questions are answered here.  Summary: it does seem possible to achieve pretty flat brew temps by adding the right amount of boiler heat during the shot.  I don't yet understand all the terminology, but it seems that this is possible to accomplish with PID alarms.  I think I'll try the same thing manually with a second dimmer switch set to ~40% power, wired to the boiler, that I turn on once the shot starts.   ;D

After a few more such mods, my machine will be called the Gaggia/Rube Goldberg Classic, and I'll be the only one who can figure out how to use it.   8)

Offline D4F

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Re: Measuring temperature in the boiler
« Reply #10 on: January 29, 2014, 11:39:21 PM »
Wow, a lot of information in this thread.  The intrashot drop can be controlled or eliminated with a PID controller, not necessarily with the PID algorithms.  I think that this is adequately discussed here

http://coffeegeek.com/forums/espresso/machinemods/571792

and seen in the youtube already noted in GUG.

http://www.gaggiausersgroup.com/index.php/topic,109.0.html

It can also be done with a steam switch separated from the solenoid so that the switch can be useful during a brew.  Also referenced and shown with video in the first link above.  It has also been done with a computer board, Arduino and equivalent.

Without belaboring the point, it is simply using the ability of the Gaggia heating system to add heat calories as quickly as cool water calories are added.  It only takes about 30% of the power or duty cycle of the elements to match the incoming cool of a brew, size dependent.

The Gaggia elements being in the boiler wall induce a time lag for turn on of energy to heat the boiler and that heat to get into the water.  Additional time lag comes from the sensor being in the wall, not in the water.  Sensor in the water may have some advantage of less lag, but the process will still have some lag.  An element in the water might heat faster, but the Gaggia is fairly rapid with the high wattage and small boiler, almost a thermoblock.  I can see a possible downside to sensor in the water for the average user.  The sensor separated from the element seems like it could lead to the possibility of overheating and melt down if the boiler was very low on water.  Perhaps why not adopted by Gaggia even though they used it on KA Proline.  I suspect that the sensor in the boiler works very well and should also control intrashot drop.

Pizzaman, Curtis, I have followed some of your work and posts at HB since you posted in CG on the PID thread.  I had not seen your specific sensor in the boiler well.  How are you controlling idle, vs heat during the brew?  Do you preheat the incoming water?

Big L, thanks for the notice :)   
« Last Edit: January 30, 2014, 01:05:36 PM by D4F »

Offline D4F

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Re: Measuring temperature in the boiler
« Reply #11 on: January 30, 2014, 12:24:31 AM »
Actually, I think all my questions are answered here.  Summary: it does seem possible to achieve pretty flat brew temps by adding the right amount of boiler heat during the shot.  I don't yet understand all the terminology, but it seems that this is possible to accomplish with PID alarms.  I think I'll try the same thing manually with a second dimmer switch set to ~40% power, wired to the boiler, that I turn on once the shot starts.   ;D

After a few more such mods, my machine will be called the Gaggia/Rube Goldberg Classic, and I'll be the only one who can figure out how to use it.   8)

Is your dimmer rated for Gaggia heater wattage?  You may be the only one dare use it :)

Offline The Big L

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Re: Measuring temperature in the boiler
« Reply #12 on: January 30, 2014, 08:26:24 AM »
Is your dimmer rated for Gaggia heater wattage?  You may be the only one dare use it :)

But of course!   8)

Offline D4F

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Re: Measuring temperature in the boiler
« Reply #13 on: January 30, 2014, 11:27:42 AM »
Glad to hear it, you will still be posting then :)

If you haven't seen the thread on PWM and heater control

http://coffeegeek.com/forums/espresso/machinemods/611316


Offline pizzaman383

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Re: Measuring temperature in the boiler
« Reply #14 on: January 30, 2014, 06:48:51 PM »
The Gaggia elements being in the boiler wall induce a time lag for turn on of energy to heat the boiler and that heat to get into the water.  Additional time lag comes from the sensor being in the wall, not in the water.  Sensor in the water may have some advantage of less lag, but the process will still have some lag.  An element in the water might heat faster, but the Gaggia is fairly rapid with the high wattage and small boiler, almost a thermoblock.  I can see a possible downside to sensor in the water for the average user.  The sensor separated from the element seems like it could lead to the possibility of overheating and melt down if the boiler was very low on water.  Perhaps why not adopted by Gaggia even though they used it on KA Proline.  I suspect that the sensor in the boiler works very well and should also control intrashot drop.

Pizzaman, Curtis, I have followed some of your work and posts at HB since you posted in CG on the PID thread.  I had not seen your specific sensor in the boiler well.  How are you controlling idle, vs heat during the brew?  Do you preheat the incoming water?
The KA thermo-well has a copper bobb (I don't know what else to call it) installed at the bottom that feeds the temperature signal to a dial gauge thermostat.  That appears to be reading the temperature of the water near the top of the outlet pipe.  I think the size of the bobb (about 1 inch long) is causing the temperature reading to be averaged a bit.  The temperature readings the PID receives are fairly stable and consistent yet are quite representative of the water temperature.  I see the temperature drop down initially at the start of the shot and the PID is giving quite a bit of juice to the heating element.  This goes on for about 10-15 seconds then the temperature starts to rise so the PID reduces the juice.  By the end of the shot, the temperature is back at the set point.

I am using a one-layer wrap of copper tubing that's tightly wound around the boiler.  I've also placed very tightly rolled aluminum foil (it's tight enough to act almost like a solid block of aluminum with just enough give to be able to be pushed into place).  This makes the preheat coil quite effective in preheating the water.  The coil holds about 2 ounces of water so it gives preheated water for about one shot.  All the modern double-boiler designs include some mechanism of controlling the heat of the water entering the boiler.  This is necessary because the time it takes for heat to be transferred inside the boiler is too slow if there is a large temperature differential.  Adding the preheat coil around the boiler does this for the Gaggia.  Other methods are possible (using a thermo-block or a second boiler) but are more hassle to implement.  Because the incoming water temperature is near the boiler temperature my water temperature only drops around 4 degrees F during the shot. 

I have a VBM DoubleDomo machine and have compared shots back to back and the ones from the Gaggia (with the preheat coil, thermo-well sensor, and PID) are pretty close in taste and consistency.  The VBM drops about 1.5-2 degrees during the shot and I think that's what causes the difference in taste.

 

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