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Homeroasters.org » BUILDING A ROASTER » Fluidbed Roaster
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Getting Accurate Temperature readings with Fluid Bed
dbick
I am just wondering if everyone that is using a homemade FB roaster is getting what they believe to be accurate bean temps? I am trying to use the Sweet Maria's roasting guidelines and I am not seeing the same events happening at the temps they say they should be happening. For example, I am not hearing any cracks until my probe reads above 425F. Here is my design.

https://imgur.com...

As you can see from the first photo my temp probe is about 1.5 inches above the perf plate in the cocktail shaker.
Am I just reading the air temp that is hitting the beans and not the actual bean temp?When I start hearing first crack but my probe is measuring 425f, do you think I am actually closer to 400F? Should I just subtract 20f or so from that reading and go by that? I do have the ability to use a second temperature probe and track them both at the same time. Any recommendations as to where I might place my second probe?

I have ordered the MasTech so I can hook this into Artisan. I would like to know if I am recording the temps at the right place.
 
coffeeroastersclub
My first impression is that: #1. your probe is too close to the inlet. And #2. your probe end is to far into the center. I would raise your probe at least 1.5 inches and have it stick into the chamber no more than 3/4".

Len
"If this is coffee, please bring me some tea but if this is tea, please bring me some coffee." ~Abraham Lincoln
 
http://www.coffeeroastersclub.com
dbick
Thank you. I will give that a try.
 
coffeeforblood
My temp probe is used only to measure the air inlet temp. It is about an inch or so below the screen that holds the beans up. I just roast empirically based on that inlet temperature. My inlet temp is about 450 - 455 F and my roast takes about 9 minutes to reach a rolling second crack. I guess what I am saying is that I have no idea what the actual bean temperature is during the process, but that doesn’t stop me from producing very consistent, tasty coffee.
 
dbick
I couldn't really get the Probe any further from the bottom perf plate because the glass tube sits into the funnel right above where the probe is inserted into the cocktail shaker. I was able to just place the first 1/4 of the probe in and I put it in as much as an angle as possible to get the tip further away from the bottom. I do think that this really helped, my temperatures were closer to what I'd come to expect. Thank you for that advice.

Very interesting idea of just measuring inlet temp and not bean temp. As a new roaster, maybe I am trying to use the temperature guidelines too much and instead should just learn based on my machine. I do have room to insert another probe below the perf plate so I think I will do that and watch what both of those temps do.

By the way. I am measuring the temps using my BBQ Thermometer made by Thermoworks. The unit is called the Thermoworks Smoke and can monitor 2 probes. The unit came with 2 different types of probes. One to stick into the meat and another to set on the grill to monitor the air temp inside the BBQ. I am using the probe that is supposed to measure the BBQ air temp. Would there be a huge difference between these two types of probes? Should I be using the one that is supposed to be inserted into the meat instead?Once my Mastech comes in(wow it takes over a month to arrive) I will use both of those probes instead.
 
ChicagoJohn
Not sure how your roaster moves the beans around, but in mine the air tends to shoot up through the center and the beans around the edge then move back down until they get into the center column of rising air again. So I put my TC tip about half way between the RC side and the start of the perf plate so that it is not in the immediate path of the center column of air.

However, in a fluidized state, hot air will be moving in the interstitial space between the beans anyway so wherever I place it, I figure I'm getting a relative measure that involves some unknown balance between air and bean surface temperature that is not in equilibrium. The main thing is that it's as reproducible as possible as a parameter to use in monitoring the roasting process.

Another thing to take into account is that TC's do not necessarily measure temperature at the tip -- the EMF they generate is from the hottest point in the TC circuit in relation to the cold junction (which is electronically determined in practice). If, for example, your RC wall gets hot and transfers that heat efficiently to the TC wires, the TC output would be affected by the RC wall temperature and less sensitive to changes at the junction / tip. So with that in mind, I use a piece of high temperature silicone tubing to limit thermal conductivity between the RC material and the TC wire.

I've built a number of hot air roasters and I've found differences temperature when first 1C happens for the same batch of beans that are no-doubt associated with various idiosyncrasies in each design. But once a profile has been determined, I've seen good batch-to-batch uniformity repeating it.

Hope this helps some.
So many beans; so little time....
 
Will2
dbick wrote:


...Once my Mastech comes in(wow it takes over a month to arrive)...


You do not have to wait for Mastech.
It suffices if you have a webcam.
Roastlogger with OCR can log data from the display image:

up.picr.de/31039426uf.jpg

OCR was not correctly set in this image, this is for informative only, instead of temperature 07 *. *°C or 17 *. *°C readed 01 *. *°C and 11 *. *°C.
Viliam
 
dbick
My Mastech arrived sooner than I had thought and I have done two roasts with it hooked up to the Artisan Software.

I am using the two TC Probes that came with it. The first probe I have placed below the Perforation plate just poking into where the hot air enters below the beans to measure ET. The second probe I put in the roast chamber off to one side where the beans fall back after being lofted to measure BT.

Now I am having the opposite problem as before. The measured temps are about 100f below what I expect them to be. The ET topped out at @400F. I am positive the actual temp is higher than that. The BT only reached around 300F even when I clearly saw the roast progressing as I expected it to. It went through a nice drying phase and moved into 1C in about 8 minutes. I got into full 2C in about 10 minutes. The coffee came out very tasty but the low-temperature recordings have me concerned that I will never get the full benefits of logging each roast if my actual temps are way different than my measured temps.

Are the included TC probes that come with the Mastech what everyone else uses or are there better TC probes that I should use?
 
renatoa
Check TC type in settings, mine arrived with wrong type, different than K.
 
allenb
If thermocouple type is correct in settings, shoot us photos of your probe setups. Getting reliable temperature feedback in a fluidbed is tricky and sometimes takes a few location attempts before being successful.

One thing to remember with sheathed probes is they have to extend into the heated area further than most people imagine in order to not read too much of the non-heated environment outside of the roast chamber walls. The larger the probe diameter, the further into the heated area they need to be to avoid this.

BT is always problematic in FB roasters due to the high percentage of roasting hot air influencing the probe versus beans. I've never been successful trying to read BT with the probe extending into the bean mass and have always had to locate the probe a few inches above the bean mass and off to one side. This usually gave me a 1C temp around 400F when in the right spot.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
dbick
Thank You.
I did have my BT probe "sheathed" inside of a copper tube that was pinched closed at the end. It only stuck into the RC about an inch and it wasn't in the direct airflow path. Before this, I was using my "smoke" TC that was stuck in about half way and the Temps I was getting were too high, about 425F at 1C.
I have ordered these that should be arriving today:

amazon.com/gp/pro...&psc=1


I will use one below the perf plate for ET and try to get the other one up inside the RC for BT. I will report back here if these worked better than the other probes.
Edited by allenb on 12-05-2017 13:20
 
renatoa
So, was the TC type correct ?
 
allenb
dbick wrote:

Thank You.
I did have my BT probe "sheathed" inside of a copper tube that was pinched closed at the end. It only stuck into the RC about an inch and it wasn't in the direct airflow path. Before this, I was using my "smoke" TC that was stuck in about half way and the Temps I was getting were too high, about 425F at 1C.
I have ordered these that should be arriving today:

amazon.com/gp/pro...&psc=1


I will use one below the perf plate for ET and try to get the other one up inside the RC for BT. I will report back here if these worked better than the other probes.


I would never consider using a sheathed thermocouple with a sheath diameter greater than 1/8" due to slow response time and the need to be several inches into the chamber being measured. The one you show the link to is not far from 1/4" diameter and at 2" long, would do fine for liquids but would be too short for measuring air. Even though the suggested minimum length for 1/4" diameter sheath is 2.5", you'd need to double that for measuring air.

I would find one close to 1/8" and plan on having at least 2.5 to 3" of insertion length to be safe. If you have trouble working with that much probe length, give it a bend.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
dbick
Yes, the probe type was correct. My new probes came in today and I will work on getting them installed tomorrow and give them a try.

allenb- So the probe that I ordered, you think it is too large in diameter to give proper air readings? Also, it is pretty long so it would completely go across the entire width of the RC. What if I could give it a bend, sort of an "L" Shape and point the tip up vertically towards the top of the RC instead of having it horizontally across the RC?

Thanks for your guy's help and opinions!
 
dbick
The Probes came in and I have installed them as such:

https://imgur.com...

The probe for the BT I have set off to one side. The idea is that it will measure the BT as they fall back down along the side.

The second probe is for measuring ET and I have it stuck in so it completely crosses the air path.

First two roasts are done with this new setup and I have a bit of learning to do. I think the probes are still measuring low. The first batch I was watching the monitor instead of the beans and the temp ET and BT temps were struggling to hit 310F-325_ after 5 minutes. But when I actually looked at the beans they were already done yellowing and were far into browning. That batch was ruined since I hit 1C in about 6 minutes. Havent tasted yet but they smell burnt.

The second batch was better since I decided to slow it down and to just watch ET and the beans themselves. 1C happened at 8 minutes at 405F BT and 427 ET which actually seems right doesn't it? 2C was at 11 minutes at 417 BT and 434 ET. I think its actually looking right.
 
allenb
The second batch was better since I decided to slow it down and to just watch ET and the beans themselves. 1C happened at 8 minutes at 405F BT and 427 ET which actually seems right doesn't it? 2C was at 11 minutes at 417 BT and 434 ET. I think its actually looking right.

ET in a fluidbed when first hitting 1C will be anywhere from 480 to 550 F in all but extremely efficient designs as in true bubbling bed technology which can allow hitting 1C with a 450 degree air input.

Second crack happens anywhere from 438 to 445 bean probe temp but can vary a lot depending on probe placement and other factors.

In many cases, moving a probe even a little downstream of an electric element can cause huge changes in sensed temperature readouts.

Allen

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
dbick
So my reading of 427 ET at 1C seems low. If I just look at the temp readings it seems like my unit is very underpowered, but when looking at actual roasting it seems powerful enough since I can easily get to 1C in under 6 minutes if I let it. I almost feel like I need to disregard the temps and just roast based on sight, sound, and smell. Probably not a great idea for a newbie right?

Just got 5lbs of Ethiopian yiggra. Hope I don't mess this up...
 
dbick
First roast of the Ethiopian Dumerso done. Here is a link to the Artisan roasting graph and a photo of the roasted beans. Please critique this roast and let me know what you think. I just roasted it this afternoon so I will let it sit until morning to taste. I can say that it smells terrific and I can even make out hints of blueberry and fruit aromas. In the photo of the beans, I notice what might be signs of tipping? Perhaps I let this roast a bit long and should have dropped it closer to 1C end?
https://imgur.com...

One more question about Artisan itself. Notice the blue dots at the bottom of the graph. Those record the airspeed setting on the speed dial of the router control. I created buttons in Artisan that I click as I raise or lower the airflow. Is there a way to label those marks? Or how can I make it so when I click the button, the corresponding setting number is displayed right there on the roasting graph, similar to how TP, DE, and 1C is labeled on the graph? Those unlabeled dots at the bottom of the graph aren't as easy to read when I try to duplicate a roast.
 
renatoa
All beans exhibit center line charring. This comes from too much heat in one ot the phases, probably at start.
Then the heat stalled in the 2-5 minute interval, with the same result in BT and RoR. Again not good, we don't want stale anything during a roast, everything must move, beans and temperatures too.
I would suggest to choose a profile from the internet, then draw a line above BT, at a distance starting with about 50C degrees at charge, and progressively approach BT down to 15-20 C degrees in the FC area. Something like this:
renatoa attached the following image:
roastplot.jpg
 
dbick
Thank you. I will try that. The centerline charring is something I have wondered about. It seems like different beans are more likely to charr. I usually don't get centerline charring with Columbian, where I get it with these Ethiopians and the Brazil I have roasted in the past. Do you think that is happening during the drying phase? I left the air control at the same setting from charge until about 5 minutes, that's when the rise started again but that is also when the temps leveled out or stalled. I could have shut the airflow down sooner to alleviate the stall but wouldn't I be charring the beans even more so at that point?
Also, can someone explain the DeltaBT blue line in Artisan? Mine is all over the place and yours is a nice smooth curve. What does that line indicate?
Edited by dbick on 12-09-2017 04:35
 
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