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Homeroasters - Home Roasting Coffee Community » BUILDING A ROASTER » Fluidbed Roaster

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Thermocouple Placement
elkayem	#1 Posted on 12/26/2018 4:57 PM
Newbie Posts: 43 Joined: March 09, 2018	It's been a while since I stopped by here asking questions about the design of my new fluidbed design over here: https://forum.hom...ad_id=5564. Anyway, I thought I would just share a bit of experience I've had regarding thermocouple placement. I have been successfully roasting for about 3-4 months now. I've iterated a little bit on where the environment and bean temperature thermocouples are place, and have a location now that I'm pretty happy with. The temperature probes can yield very different measurements, so this seems like a fairly critical detail that I haven't seen too much about on these pages. Just for a bit of background, my roaster design is posted over on github at: https://github.co...feeRoaster, based on a variant of the bake-a-round and cocktail lid fluid bed roaster that appears on many of these threads. I think a drawing is a lot easier than trying to describe in words where I placed the thermocouples. See my crude drawing, attached. The bean temperature probe is shielded from the direct air flow, about 3/4 of the way to the edge of the shaker. It comes into direct contact of the descending beans near the edge. The environment temperature probe is right in the air flow, and consistently measures temperatures 50-60 deg F higher than the bean temperature probe. I've also attached a figure showing the temperature profiles, recorded by the SD card I included in the roaster electronics. The bean temperature is controlled to track the Control Value. For a point of reference. the beans hit first crack at about 390 deg F using this placement. I'm pretty pleased with the results, so am done (for now) tinkering with this design. elkayem attached the following images:


BenKeith	#2 Posted on 12/27/2018 10:46 PM
Pounder Posts: 485 Joined: April 21, 2014	Totally not where I would put it, but if it's giving you the results you are looking for, that's all that counts. I control my roast by ROR and bean temp (neither of which most people would recommend) so I don't want the probe in the air stream. It actually took me a number of trial and error tries in different locations the give me the results I was looking for and found probe placement to be extremely critical for my method of control.


elkayem	#3 Posted on 12/27/2018 11:30 PM
Newbie Posts: 43 Joined: March 09, 2018	Hi BenKeith, I wonder if my diagram or explanation wasn't clear. My bean temperature probe actually is outside of the airstream. Also, I use the bean temperature thermocouple (not environment) as the control variable. On the diagram, it is the orange thermocouple, not the red one. I purposely have it on top of the metal shield, which blocks the air stream, and places it in contact with the descending beans. I shared this post because I found a dearth of information regarding where exactly one should place the thermocouple. It was a matter of trial and error for me. I am genuinely curious about where others have placed their probes. What do you recommend?


BenKeith	#4 Posted on 12/28/2018 12:20 PM
Pounder Posts: 485 Joined: April 21, 2014	Sorry, failed to look that close at the diagram you had, just looked at the picture. Where you are showing the bean probe is a similar location as mine. Mine is a super fast exposed bead wire probe located in the tapered funnel about a 1/2" from the vertical wall and it sticks up about a 1/2" off the bottom. I use the exposed bead because I don't want the buffering effect you get from the enclosed metal probes. Again, totally opposite from what most seem to recommend, but like I mentioned with yours, I'm very happy with the results and the degree of control I get, and that's all that matters. I run the ET probe just above the bean column, high enough that the beans don't contact it, however, most of the time it's not even plugged in. I've been running this setup so long, it's basically in autopilot and rarely even look at the ET. I just load the action table I want and the PID does almost everything else.


CK	#5 Posted on 12/28/2018 5:28 PM
1/2 Pounder Posts: 239 Joined: December 07, 2018	Nice job, very tidy. For my FB, the thermocouples are 1. in the inlet airflow below the RC, and 2. in the exhaust airflow leading to the chaff cyclone. I haven't tried other placements, but this seems to work on this manual roaster. This is the same way that Ikawa Pro V3 roasters are built. Do your github pages explain how to integrate the LCD/Arduino operation buttons? I'm trying to learn how to do the same with an Arduino/TC4 setup. The idea is to have a number of profiles stored in the roaster so I could roast without being connected to Artisan.


BenKeith	#6 Posted on 12/28/2018 11:12 PM
Pounder Posts: 485 Joined: April 21, 2014	There a two popular programs to do what you are wanting. RoastLogger TC4 and aArtisanQ_PID. I use RoastLogger, but Tom Coxton wrote it and has not done much to support it in the past couple of years so I would I would not recommend starting off with that one, since support is not readily available. aArtisanQ_PID was written by Brad (Greencardegan) and is still very actively supported on this site. He is also selling TC4's. He also supports a stand alone mode that does not require a computer, once you load your profile into it. I think a couple others have cards and programs written also, but don't get on here enough to keep up with who has what. I run in the PID mode but to get the one setup to run a good profile in the PID mode requires a good bit of a learning curve. One is understanding how to tune a PID, the other is working out a profile for your roasted and the beans you are roasting. A lot of people on here run the TC4 but from I get the feeling not many actually use the PID function to control their roaster, so if you are wanting to run it the PID mode, not sure what support you can get. It's definitely not a plug and play mode. The buttons are mainly only needed in the stand alone mode. For that, you only have two profile options you can store in the TC4 at one time using aArtisan Q_PID. For more than that, you have to load the one you want and over write one of the existing profiles you have stored. Depending on which program you opt to use determines the function of the buttons. RoastLogger does not support a stand alone operation. I guess I should clarify. I have several TC4's, and while I run RoastLogger on the computer an in the TC4 I use with the computer, I also have a couple of them setup to run in the Stand Alone mode and for those I run aArtisanQ-PID. Brad also has an app you can download to your Droid phone and use your phone to control the TC4, but you have to install a Bluetooth module in it. Edited by BenKeith on 12/28/2018 11:33 PM


renatoa	#7 Posted on 12/29/2018 2:29 AM
Administrator Posts: 2598 Joined: September 30, 2016	Exhaust air as BT is not the most accurate way to measure beans temperature, ask Gene guys if they are pleased with this approach... You can figure how much out of way looking at your FC temperatures, if more than 190-195C, then you mainly measure hot air instead beans temp.


elkayem	#8 Posted on 12/29/2018 8:44 AM
Newbie Posts: 43 Joined: March 09, 2018	Quote BenKeith wrote: Sorry, failed to look that close at the diagram you had, just looked at the picture. I realize now that the photograph was very misleading, making it harder to decipher my setup! I've updated the photo (attached) to highlight both thermocouple locations. I have also color coded the diagram and photo to match the bean and environment temperature lines on the profile plot. Hopefully this will reduce confusion. Both thermocouple beads are exposed and fairly responsive. I purchased an inexpensive metal probe off Amazon (5mm x 50mm), removed (and threw away) the actual thermocouple inside of it, and cut off the end of the metal sheath with a Dremel. I then threaded two thermocouples into the sheath, exposing both and wrapping the bean temperature sensor back on top of the metal sheath. elkayem attached the following images:


elkayem	#9 Posted on 12/29/2018 8:57 AM
Newbie Posts: 43 Joined: March 09, 2018	Quote CK wrote: Nice job, very tidy. For my FB, the thermocouples are 1. in the inlet airflow below the RC, and 2. in the exhaust airflow leading to the chaff cyclone. I haven't tried other placements, but this seems to work on this manual roaster. This is the same way that Ikawa Pro V3 roasters are built. Do your github pages explain how to integrate the LCD/Arduino operation buttons? I'm trying to learn how to do the same with an Arduino/TC4 setup. The idea is to have a number of profiles stored in the roaster so I could roast without being connected to Artisan. Thanks CK! Regarding your question about my github page, I have to confess the details are fairly light about the electronics. Sooner or later I'll add more detail. It is a work in progress. I do think that someone with a modest familiarity with electronics and the Arduino environment could figure out the wiring without too much trouble. The code itself is pretty clear on which buttons are attached to which pins. The code does save a (configurable) 9-segment profile onboard in flash memory, and does not require a computer connection. At this point, it stores just a single profile, not multiple profiles as you are looking for. It's enough for me and my finicky espresso tastses, but I could see others wanting something more flexible.


JackH	#10 Posted on 12/29/2018 3:41 PM
Administrator Posts: 1809 Joined: May 10, 2011	It is a nice setup that you have. Good work! I guess if the results and readings are repeatable, it works. I have a turbo roaster and have the environment probe in the center of the chamber in the air and the bean probe through the side into the bean mass. I find predictable values occur that allow me to roast with good consistency. ---Jack KKTO Roaster.


Linnaeus	#11 Posted on 01/17/2019 7:37 AM
Newbie Posts: 49 Joined: September 12, 2017	Another idea for the mix. You can bend thermocouples (so long as you don't crimp them) and they sell much longer units as well. The longer the thermocouple, the more averaged the reading will be - as it is being measured over a larger area. What I'd do is keep the placement as is, get a longer thermocouple (6 inch?) And then right where it enters the chamber, bend it upwards and to the side so that it is out of the airstream.
	Web

renatoa	#12 Posted on 01/17/2019 7:50 AM
Administrator Posts: 2598 Joined: September 30, 2016	The long thermocouples have a sweet spot, not longer than one inch, usually the tip area. They aren't longer to sense equally the entire length, but to facilitate temperature sensing in a deep narrow spot. If I pinch my 8cm long / 3mm probes with two fingers in the middle, i.e. at 4 cm from the tip, I could have no temperature change for long time, maybe even a minute, compared with instant reading if I grab the tip of the probe.


greencardigan	#13 Posted on 01/17/2019 4:45 PM
1 1/2 Pounder Posts: 1179 Joined: November 21, 2010	Quote BenKeith wrote: you only have two profile options you can store in the TC4 at one time using aArtisan Q_PID. For more than that, you have to load the one you want and over write one of the existing profiles you have stored. Just a little correction here. The aArtisanQ_PID can support more than two profiles stored on the TC4. I haven't tested the max number but it should store quite a few. The number of profiles option in the user.h file is used to let the sketch know how many profiles you have loaded onto the TC4.


CK	#14 Posted on 01/17/2019 10:26 PM
1/2 Pounder Posts: 239 Joined: December 07, 2018	Brad, thanks for clarifying that the TC4 can handle more profiles in its memory. When I learn about this aspect, it will help greatly in streamlining the work flow for roasting a variety of beans in stand alone mode.

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