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daduck748
Senior Member


Joined: 13 Dec 2012
Posts: 157
Location: California, USA
Expertise: Just starting

Espresso: Gaggia Classic (2012)
Grinder: Breville BMF600XL
Posted Fri Mar 8, 2013, 12:20am
Subject: Re: Custom Thermocouple for Gaggia Classic
 

Here's a very custom thermocouple that I built.  This is actually version 2.0.  Version 1.0 is currently inside the boiler of my Classic taking temps.  Version 1.0 is pretty accurate (-1 degree), but when I put it in the boiler, I was reading temps up to 235F, which means the heat from the boiler wall was leeching into the shaft, down to the thermocouple, so I redesigned it.

In version 2.0, the thermocouple is obviously in the brass pill, which is heat isolated from the boiler wall by way of the alumina ceramic tube.  The upper brass bushing is press-fit into a special adapter, which I'll be performing later as an upgrade from version 1.0.  Everything is liquid, thermal, as well as electrically isolated.  Hopefully, the reading on my "PID" will read something closer to 212F, if not 212F on the dot.

This may not apply to anyone, but it is related to the topic matter: custom thermocouple for Gaggia Classic.

daduck748: IMG_2673.JPG
(Click for larger image)

 
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daduck748
Senior Member


Joined: 13 Dec 2012
Posts: 157
Location: California, USA
Expertise: Just starting

Espresso: Gaggia Classic (2012)
Grinder: Breville BMF600XL
Posted Fri Mar 8, 2013, 12:21am
Subject: Re: Custom Thermocouple for Gaggia Classic
 

Oh, I guess I do have a picture of Version 1.0.

daduck748: IMG_2619.JPG
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D4F
Senior Member


Joined: 15 Mar 2012
Posts: 1,997
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Baratza Forte-AP
Posted Fri Mar 8, 2013, 10:37am
Subject: Re: Custom Thermocouple for Gaggia Classic
 

How and where did you insert and anchor this?  New holes, O-ring seal or tight threads?  Looks interesting but I can't quite picture where you have it going into the machine.  In place of the steam valve?

 
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daduck748
Senior Member


Joined: 13 Dec 2012
Posts: 157
Location: California, USA
Expertise: Just starting

Espresso: Gaggia Classic (2012)
Grinder: Breville BMF600XL
Posted Fri Mar 8, 2013, 11:59am
Subject: Re: Custom Thermocouple for Gaggia Classic
 

I am one of the LEAST of lazy people I know, but when it comes to THINGS I use every day, I steer away from messing around with it TOO much, in case I can't get it back together before the next time I have to use it, so I have not taken the boiler out of the machine to do anything with it at this time. That probably wouldn't happen until I have a spare espresso machine so I can REALLY play with this one.  The wife loves her coffee too much to be DOWN for a day.  Every time it's down, she runs to Starbucks and I hear complaints... "You didn't make me coffee, so I had to run to Starbucks... and it always sucks!"  So keeping the machine running is really in my best interest as far as coffee goes.

Just for the sake of gathering data, yes, I temporarily sacrificed the steam valve for the probe.  No new holes.  No new threads.  I just reused the conical o-ring that comes with the steam valve, since it is already nicely shaped for the opening.

The probe comes all the way down near the bottom of the boiler, where the water is nearest the output temperature you can get before any suction, siphoning, or too much more infusion of ambient heat happens before the water leaves the shower head.

Again, I tested this probe in a pot of boiling water and this one is short 1.8F.  Still not too bad.  I've seen other thermocouples off by as much as 14F, so I can live with a small calibration value.  I went as far as to shove the entire probe, up to the shield and boiled it for about 15 minutes.  No shorting, so it has been sealed well.  The temperature is steady at 210.2F, no matter where I put the probe and whatever else is touching it, so the alumina ceramic is also doing its job isolating thermal transfer to the pill.

Just like all my other custom thermocouples, it is extremely sensitive and very fast response time and I am logging pretty good data.  As time permitted, I've installed a "reverse SSR", for the lack of a better term (It's a SSR that switches at 120V-300VAC rather than 3-60VDC and gives me a 5V signal at the other end) that I connected to the lower thermostat so I can log the internal water temp in relation to WHEN the thermostat turns on/off the heating elements.  It's not working out the way I planned... yet.  Maybe the R-SSR is faulty.

The main idea is to obtain the end-water temperature, based on starting and ending water temps inside the boiler, as opposed to starting and ending temps of the boiler (granted, with offsets).  My data will also require offsetting the internal water temps as well, since the only way to really control the temp is to measure the water temp in the puck as you're pulling shots which is impractical, but the margin of error between internal water/resulting-water temps is much narrower than boiler/resulting-water temps.  The result that I'm after is to narrow the top/bottom water temp range so I can control the taste of the resulting coffee.  Although, with a wide brewing temp range and calling it "good" because the beginning and ending are within textbook numbers I'm sure is satisfactory, but taking it further and controlling taste by controlling water temp is totally something different.  Who knows?  Maybe the hardware that the Classic comes with won't allow such precise control, but at least the concept is there, and I may have to take the concept a little further and building a boiler that will allow this.

The process is this: now I have a way of getting good "real-time" water temps (as good as it gets, I suppose), the reverse-SSR comes into play to log when the heaters kick in, and log the behavior of the Classic.  This will basically give me the information I need to simulate a stock Classic, using a PID and thermocouple in place of the thermostat, since I can't install both at the same time.  Once I have successfully simulated a stock Classic, I can start making improvements to the machine, based on how it is out-of-the-box.  The R-SSR is only temporary for the sake of data collecting, not part of the end product.  All the switches will be replaced and microcontroller controlled and operate at low voltages.

It's also taking a while to get put my espresso controller together since it got really busy at work the last few weeks and I'm also contemplating whether I should build the housings based on the mini-modules I've collected for this project or build a custom PCB.  Decisions-decisions.  But delays are mostly due to lack of time.

Sorry for the long write-ups.  In my line of work, I work with engineers and scientists and everything is about data and precision.  Many of my customers are in the semiconductor industry so detailed control is essential.  A lot of my personal works utilize some technologies I implement for my customers so I also apologize if I can't expose details of manufacturing processes of my parts I show here or elsewhere.  My write-ups are probably not for everyone, but I like to write as much detail about my stuff as I can... so people can see what is possible to be done.

 
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daduck748
Senior Member


Joined: 13 Dec 2012
Posts: 157
Location: California, USA
Expertise: Just starting

Espresso: Gaggia Classic (2012)
Grinder: Breville BMF600XL
Posted Fri Mar 8, 2013, 12:11pm
Subject: Re: Custom Thermocouple for Gaggia Classic
 

daduck748 Said:

Just for the sake of gathering data, yes, I temporarily sacrificed the steam valve for the probe.  No new holes.  No new threads.  I just reused the conical o-ring that comes with the steam valve, since it is already nicely shaped for the opening.

Posted March 8, 2013 link

Just so its clear, the stock steam valve is likely going to be tossed/modified so I can keep the probe in the water.  Steam will be controlled by the espresso controller anyway and most likely will be solenoid-valve or servo-valve activated.  We'll see when I get that far.

 
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D4F
Senior Member


Joined: 15 Mar 2012
Posts: 1,997
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Baratza Forte-AP
Posted Fri Mar 8, 2013, 9:32pm
Subject: Re: Custom Thermocouple for Gaggia Classic
 

daduck748 Said:

The probe comes all the way down near the bottom of the boiler, where the water is nearest the output temperature you can get before any suction, siphoning, or too much more infusion of ambient heat happens before the water leaves the shower head.

Posted March 8, 2013 link

Looking at the parts diagram I see the upright tube in the boiler.  I thought that the water exited from the top of that tube fairly high in the boiler and passed out the group while the incoming water somewhat swirls in the bottom from the OPV.  Would the probe be best situated at exit tube height.  I suppose ideally a thin flex probe could be threaded into the down/exit tube.  Do you have a different understanding of the flow?

Click Here (www.partsguru.com)

 
D4F also at
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daduck748
Senior Member


Joined: 13 Dec 2012
Posts: 157
Location: California, USA
Expertise: Just starting

Espresso: Gaggia Classic (2012)
Grinder: Breville BMF600XL
Posted Sat Mar 9, 2013, 12:09am
Subject: Re: Custom Thermocouple for Gaggia Classic
 

I would agree.  As the pump pushes water into the boiler, it would fill the empty space in the boiler, above the top of the tube and flow into the basket.  The compression of the coffee grinds is actually the main factor in boiler pressure, which causes the excess water/pressure out the OPV.

I thought about that but decided to get the sensor below the top water-line (top of the tube) since when we're not pulling shots, that empty space is used for producing steam.  I didn't want to get the sensor too high, otherwise I'd be measuring a mixture or steam and water, not something I wanted at this time.  Another reason why I chose a thinner ceramic tube is so I can shove another sensor above the water-line.  Why?  Measure steam temp?  I don't know.

Anyway, there are all kinds of factors to consider when in design mode.  Thanks for pointing that out.  Anyway, at least by getting the sensor in the water, I can detect cold water and current temperature in real-time, something a sensor on the boiler wall can't do, or won't be able to detect it accurately and quickly enough.

The only thin I would change on the upper bushing would be to thread the exterior so I can teflon tape it and turn it into a threaded hole in the adapter.  As of now, I have to make a new thermocouple every time I make a sensor.  I'll learn one if these days.

 
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daduck748
Senior Member


Joined: 13 Dec 2012
Posts: 157
Location: California, USA
Expertise: Just starting

Espresso: Gaggia Classic (2012)
Grinder: Breville BMF600XL
Posted Sat Mar 9, 2013, 12:18am
Subject: Re: Custom Thermocouple for Gaggia Classic
 

I've developed another idea for an accurate thermofilter which I will hook up to my controller.  This will give me water temp, boiler wall temp, heater on/off as well as basket temp, all on the same timeline and scale.  I won't go into detail about the thermofilter here, since it's a bit off-topic.  That and my idea worked well but I didn't do such a good job on it and the ceramic cracked and became a one-hit wonder.  I have to make a new one.

All these sensors require so many data lines that I can't have more than one sensor, so I have to build a I2C-SPI bridge to hook up to 8 sensors to the single I2C interface.  That will take me a little time, since I have to build the PCB for it.  The bridge of choice only comes in a surface mount package so a quick breadboard won't help me.  I'm going a little too off-topic so I'll keep you posted.

 
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D4F
Senior Member


Joined: 15 Mar 2012
Posts: 1,997
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Baratza Forte-AP
Posted Sat Mar 9, 2013, 10:30am
Subject: Re: Custom Thermocouple for Gaggia Classic
 

While you are not using steam or opening the boiler it would be interesting to generate your temperture plots with the long probe and then a similar plot with a short upper probe and see how they overlay. Should be essentially all water under pressure.  

How about figuring a hole through the group so that it is a tract for a probe that ends in the outflow to the group.  Seems like a 1/8" hole, or larger for the insulsted probe, through the side of the group could end in the water flow.  Another thought is to find a way to use #22,

Click Here (www.partsguru.com)

dispersion plate or "rose holder" as a holder for a sensor, again wiring probably bored in.  Sounds like machinists fun :)

 
D4F also at
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daduck748
Senior Member


Joined: 13 Dec 2012
Posts: 157
Location: California, USA
Expertise: Just starting

Espresso: Gaggia Classic (2012)
Grinder: Breville BMF600XL
Posted Sat Mar 9, 2013, 5:01pm
Subject: Re: Custom Thermocouple for Gaggia Classic
 

I actually do have a new design for a dispersion plate.  I purchased some brass plate to machine it out, but it turned out the plate is too thin and wouldn't work, so I'll just do it out of aluminum, since I have so much in the shop.  I'll revisit that later.

The problem with putting the sensor in the dispersion plate is that it would require modifying the brew head and possibly the boiler to wire it up.  That's mostly because the dispersion plate sit totally inside... well, everything.  Drilling would/could introduce leaking.  I originally thought the thermostats actually touched the water, but now that I find out that isn't true, the game changes.  I don't like introducing holes, especially below the water-line, in case there are stagnant leaks.  Leaks under pressure only occur for about 30 seconds at a time, while you're brewing.  Stagnant leaks will occur all-day, which I'm not willing to deal with.  LOL

Although I'm not a huge fan of Simonelli, I do like their portafilters and all the little bits intheir groups.  I even thought of making a new group for the Classic that fits a Simonelli portafilter.  So building my own group would allow me the flexibility to install whatever sensors of flow I would like.  I just haven't been that adventurous to pull the machine apart that much... yet.  This is an interesting bit because visually, it looks like the Gaggia and Simonelli portafilters are very similar.  I did pose the question in the forum somewhere but I didn't get any reply.

 
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