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Custom Thermocouple for Gaggia Classic
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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 Wed Mar 20, 2013, 12:53pm
Subject: Re: Custom Thermocouple for Gaggia Classic
 

I don't know since I had to adjust the calibration for the thermobasket and reprogram the Arduino last night.  It was already midnight or so.  I hadn't hooked any other inputs, so I don't have that data.  It was a first try with the new thermobasket.  I still have to get a bridge built so I can get more sensors installed.  I'll let you know.

The total volume was roughly 1.75 oz after it was done.  I did not do any surfing.  I waited until the temp stablized, at around 210F or so before I hit the brew switch.  If there is no drastic drop in water temp, then there was no drop in water temp.  The sensor just sits in the middle of the puck and does its thing.  The datalogger just records what the sensor is telling it.  It's just raw data.

I'll let you know when I get more info.

 
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D4F
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Joined: 15 Mar 2012
Posts: 2,026
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Baratza Forte-AP
Posted Wed Mar 20, 2013, 1:05pm
Subject: Re: Custom Thermocouple for Gaggia Classic
 

If I interpret correctly you are saying 1.75oz and the time, assuming seconds on the bottom of the graph, was from say 75 to 250 or about 175 seconds.  If that is the case, then the temperature stability is also explained by the slow flow rate.  Little cold calorie/water input.  As noted, it was your trial to test the equipment and may look different at realtime espresso flow rate.

 
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 Wed Mar 20, 2013, 1:10pm
Subject: Re: Custom Thermocouple for Gaggia Classic
 

D4F Said:

Click Here (www.ebay.com)

The seller mentions plastic and teflon as the coating.  On the coper tubing, you can solder the tip and not drink the brew from that run, or get realatively safe solder.  Copper water pipes are soldered without lead.

Posted March 20, 2013 link

Wow, cheap.

Just make sure you calibrate the thermocouple since all thermocouples are off to some degree.  Mine all seem to be around <1% off, but I have seen them as much as 15F (~7%) off.

Be careful of plastic jackets as they don't like high heat too much.  Even if they don't melt, they become extremely pliable.  Depending on grade, teflon can handle as much as 500F, which should be plenty, but not all teflon can handle this high heat.  The portafilter shouldn't get that hot, 250F at max (I haven't measured it).

But that's pretty cheap for a thermocouple... especially with the connector built into it.

 
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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 Wed Mar 20, 2013, 1:23pm
Subject: Re: Custom Thermocouple for Gaggia Classic
 

D4F Said:

If I interpret correctly you are saying 1.75oz and the time, assuming seconds on the bottom of the graph, was from say 75 to 250 or about 175 seconds.  If that is the case, then the temperature stability is also explained by the slow flow rate.  Little cold calorie/water input.  As noted, it was your trial to test the equipment and may look different at realtime espresso flow rate.

Posted March 20, 2013 link

Oops, sorry.  No, the X-axis is by row, not by seconds.  The Arduino is programmed to sample approximately every 250 milliseconds.  It may fluctuate a little on each count, since the Arduinos are pretty low speed and may miss the 250ms mark.  The condition is as so (in psuedo-code), "If wait_time is equal or greater than 250ms, take another sample", so each sample is roughly 250ms, plus a little bit.  So, you take your range and divide by 4 to get actual time.

According to the the chart, it looks like ~35-40 second shot, but that may be a bit optimistic.  However, I just hit the brew switch until the 2oz glass was full.  After the crema settled, the liquid was roughly 1.75oz.  I left the PF in the group head a few seconds while I pulled the glass, but that is not evident in the chart.  I'll have better charts with actual time intervals later.  I don't have a RTC (Real-Time Clock) on my portable Arduino so I can't log time.  I have it on my dev board at work, which is not so portable.

 
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D4F
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Joined: 15 Mar 2012
Posts: 2,026
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Baratza Forte-AP
Posted Wed Mar 20, 2013, 1:42pm
Subject: Re: Custom Thermocouple for Gaggia Classic
 

Thanks for the explanation of the time, makes more sense.

The thermocouples are rated to 399F, so no problem.  I acutally cut off the connector and hooked the wire to a PID controller.  Thermocouples are cheap on Ebay, and these were available in the US. Calibration is of course always worth checking. The seller mentioned plastic, but then said teflon, so not sure what they acutally are, but other sources are available for fiberglass and teflon.  I noted thes just in case others are interested in inexpensive thermocouples.

I hope others get interested, not just you and I :)

 
D4F also at
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daduck748
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Joined: 13 Dec 2012
Posts: 157
Location: California, USA
Expertise: Just starting

Espresso: Gaggia Classic (2012)
Grinder: Breville BMF600XL
Posted Wed Mar 20, 2013, 2:11pm
Subject: Re: Custom Thermocouple for Gaggia Classic
 

Back to custom thermocouples, my new alumina ceramic tube came.  This time with a 1/4" OD and... I forget the ID, but it is enough space for 3 pairs of fiber-jacket (that's just what I have to work with).  The new Version 3.0 probe will have provisions for a low-level water sensor, high-level water sensor, and a steam-sensor.  I don't have a bridge yet, so I won't be able to hook this up properly for some time.  At least I have the material to start planning the new probe.

The probe will have three brass pills along the length of the ceramic tube.  Keep in mind, I have to use a diamond blade to cut the ceramic tube, and it's still not that easy.  It still cracks and chips, even with a diamond blade.  I'll have three sets of wires coming out the top.

Since the bridge is the bottleneck (outside of available time), I may have time to design in a steam port to get it ready for the steam solenoid while I'm at it.  We'll see.  I may need to find a chunk of brass to make it out of too.  My steam valve is an aluminum version.  My probe-bases have been aluminum too (also what I have to work with in the shop).  That way, it can be the final version of the probe and I'll be done with water and steam temp sensors.

The internal sensor is working so well it seems, that the external M4 thermocouples almost seem silly.  I still have to gut the machine and rewire to the PIDruino (what a name).  I found some quick disconnect terminals in inventory that I'll probably take home and cable up.  I don't want to cut and splice anything inside.  I'll be gutting and replacing all the cables and connectors... just in case I ever want to put it back to stock.

 
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daduck748
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Joined: 13 Dec 2012
Posts: 157
Location: California, USA
Expertise: Just starting

Espresso: Gaggia Classic (2012)
Grinder: Breville BMF600XL
Posted Wed Apr 24, 2013, 3:06pm
Subject: Re: Custom Thermocouple for Gaggia Classic
 

I finally had a chance to work on the new Version 3 thermocouple.  Anyone following this thread might remember buzzes about version 3 and version 4... well, the design has changed (verbally/textually) a bit, while the actual part has changed a lot!

The mount was made from a larger block of aluminum.  I would prefer brass, but I guess I can do that later.  It's a bigger chunk to accommodate the steam port.  Yes, I decided to just do it, since it was just an extra hole to be drilled and tapped.

The rod only has two sensors instead of three.  I figured there really isn't any need to measure the steam temp, since what you're really looking for is water temperature under pressure which equates to steam/amount of steam.  I don't think anyone (me) is worried about that anyway, so I left it off.  So obviously, there is a upper and lower sensors for upper and lower water temps.

The upper sensor is what the PIDruino will use to go by.  The lower sensor will provide a value to help minimize temp overshooting, reducing surfing effort.

The "rod" as I call it is solely attached to a modified stainless steel bolt at the top.  This way, I don't have to remake the mount each time I want to make a change.  The bolt comes off, taking the sensors with it, leaving the mount intact.  This will come in REALLY handy when I have my steam wand reinstalled.

As mentioned above, I drilled and tapped a 1/8 NPT steam port.  I haven't planned it further than that yet, but it will eventually have a solenoid valve or motorized actuator attached between the steam wand and the steam port.

This part is right off the press so I'll have to calibrate it and test it tonight.

I tested the lower sensor already and this one is way off, but I calibrate it in the software anyway.

Enjoy.

daduck748: IMG_2952.JPG
(Click for larger image)

 
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jonr
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Joined: 25 Jun 2013
Posts: 304
Location: Americas
Expertise: I love coffee
Posted Sun Jun 30, 2013, 8:49am
Subject: Re: Custom Thermocouple for Gaggia Classic
 

Nice work, any new news?  

In looking at the response time graphs in post #2, it looks like even a fast thermocouple might take 5 seconds to read a 1 degree temperature change.  That's a pretty long time when you are dealing with a 25 second shot and any significant change in conditions (like incoming cool water).

You probe reminds me of something on the Kitchenaid/Gaggia machine.  See parts diagram here, page 4, part #2:

http://www.partsguru.com/KitchenaidGaggia.html
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jonr
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Location: Americas
Expertise: I love coffee
Posted Thu Aug 8, 2013, 8:46am
Subject: Re: Custom Thermocouple for Gaggia Classic
 

It would be very interesting to see graphs showing the temperatures from the internal and external probes during various conditions.  If the lags/offsets/influences can be accurately determined, then a computer may be able to make an external probe (easier to implement) almost as accurate as an internal one.
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daduck748
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Joined: 13 Dec 2012
Posts: 157
Location: California, USA
Expertise: Just starting

Espresso: Gaggia Classic (2012)
Grinder: Breville BMF600XL
Posted Thu Aug 8, 2013, 11:35am
Subject: Re: Custom Thermocouple for Gaggia Classic
 

Anything is possible, my friend.  Things are more possible when you implement "smart" devices into host devices, kind of like putting Einstein's brain into Frankenstein's head, or so to speak.

Close friends and family, and some people on this board I PM know that I have a "can do/anything is possible" mentality, and that's basically what my business is based on.  However, that's only an attitude.  I too realize that in reality, there are limits to "Anything Is Possible", as contradicting as it may.

I have a SD module in my PIDuino, but it stopped working when I dropped it from the workbench some months ago.  I don't think I posted about that, but... it did happen.  While I was working on it, I hadn't realized it was still connected and my foot yanked on the wires as I walked off and there was a loud SLAP! against the concrete floor.  Minimal damage to the housing but the RTC stopped working, the SD stopped working, and the LCD started displaying some crap.  Everything was replaced, except the SD module, since that's the only part I didn't have spares of.  It hasn't worked since.  I've tried reproducing the system on-bench (with a cheap Chinese SD module) and there seems to be some library incompatibility issue I don't have time to track down.

Long story short, I can't provide graph data at the moment.  I'll take me away from a very hot project that I've got going right now, but I'll share my experience here.  I do have two custom thermocouples, all solid brass pill-bodies, for best thermal conductivity (that can be easily obtained); one on the outside (where the old tstat goes) and one in the water (where the steam port mounts) which the pill sits just under the water-line.

So, I've only been watching the numbers as I'm doing ANYTHING on the Gaggia.  Of course, I'll stand there just watching the numbers as the PIDuino is trying to stabilize the temps.  I have (had) my settings a little more aggressive because my TC is in the water, so it does cross the target temp quite often (all the time).  Is that good for temp stability?  No, but that's just how I had it.  After the passive preheat implementation, I've reduced the aggressiveness but it still crossing the TP quite a bit.  The good thing about that is I can visually monitor both sensors.

This is what I've noticed.  There is definitely a lag between internal and external temps.  Yes.  However, the charts, if they may, are never equal.  Set the lag-time aside, the peaks are never the same.  If you had graphs of both internal and external sensors, shift the graphs to match the pattern, they would not be proportional with each other.  Scientifically, I'm sure you could take x, y, delta, i, sigma-this and sigma-that to explain why they won't match up, but the point is, they don't match.

During a stagnant condition (for all practical purposes) and cooling, everything is cooling down because the heaters are off.  What do you think is cooling first?  What do you think is cooling "faster"?  It's the boiler wall, since it is outside, exposed to more cool air.  The water cools slower because it is surrounded inside a hot chamber.  The boiler is what cools, then drags the water temp down.  Have you tried one of those Thermos vacuum coffee mugs?  That vacuum isolates thermal loss extremely well!  I've had a cup of coffee last (HOT) for nearly 4 hours!  The point is, the boiler temp is what drags the water temp down... or up.

During heating, the heaters are on and the boiler wall starts getting hot(ter).  The water temp is still dropping at that point.  Depending on how much power you put to the heating elements, when the boiler gets hot enough, the water temp starts to rise.  The water temp usually does not hit the low-point that the boiler hits, so there's your first evidence that the graphs are not the same.  As you probably already know, the lag-time is relative to the mass of the boiler.  In liberal science, I guess you can call that "lost in translation".

During a pull, there are many different external elements at play.  Some people here have done the passive preheat mod and it helps.  As D4F mentioned, an OPV between the pump and coil will reduce warm water loss (which is something I'll consider, but those OPV are quite expensive, so off the shop I go for a design session).  In this sense, the volume of incoming cool water is minimal.  For others with no such preheater mod, the volume of cool water is at best, devastating.  With that said, let's assume no preheat and no pre-coil OPV.  The water temp quickly drops, dragging boiler temps down.  Without the "smarts", your pull will drop to about 160F or so by the time the pull is complete.  With a standard PID, the PID is confused and wants to equalize and tries really hard (sensing greater delta), kicks the heater into high gear and you overshoot.  In that case, you probably will end your shot at 215F or higher.  You are half correct when you mention the system should be an open loop system (unless I'm understanding incorrectly).  Once the pull is started, the system should go into open-loop mode, but there's really no magic number.  Yours is 80%, which I'm not doubting since you've done the math and I haven't.  However, 80% may be ideal in an extremely controlled environment.  We live in the real world where "The Butterfly Effect" is with us.  Yes, I do believe in that, even on a small scale.  The seasons change, which changes the ambient temps, which will affect heating and cooling of the boiler wall.  Then see "stagnant condition" above.  Your home may be 70F while mine is 85F (wow, that's hot, but just to illustrate).  Anyway, back on topic, as the cool water enters, dragging water-temp down, the boiler temp is also dragged down.  Same "lost in translation" concept applies.  There's your second evidence that the graph is not equal.

Now, during a stagnant condition, the boiler temp affects the graph in both cooling and heating.  During a pull, the water temp is what affects the graph.  With a mass in between, creating 2 losses in translation, in two different conditions, there is no way the graphs will be proportional, so you cannot simply say, "external is always 5% lower, so I'll just take the numbers, multiply by 5%, and shift by 3 seconds".

Sorry if that was more information that you were asking for.  That's just my experience and observation with my system.  But the short-short response is, you will not be able to mimic an internal sensor (actual water-temp) with an external sensor.  You may get close/lucky, but because of the losses in translation, in two different situations, it won't be exactly.

D4F said to me a LONG time ago, the water-temp at the shower is an offset of what the PID is actually regulating to.  Here's where I'm a hypocrite.  It's espresso, not a science project.  LOL

Let me know if I can be of some help here.

 
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