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Thermocouple Location in Fluidbed
PaulHilgeman
I have the typical fluidbed roaster that I have been working on. I am trying to find the ideal location for the thermocouple.

So far the only location of the 3 roasts that I have done that made any sense was to have the TC (Bare) right inside the glass, about 1" from the top of the bean bed. This seemed to correlate with what I would expect from the roast +/- 10 degrees.

I have also tried to insert it farther into the bean mass, and am seeing temps much closer to the air temp (about 550 degrees)

So, two questions:

1. What type of thermal mass (thermowell or otherwise) is on/around your Bare TC tip

2. Where in the bean mass are you placing the TC?
 
jkoll42
My experience was that temp readings were most accurate where the bean mass returns to the hot air column.

Do you have too much airflow going into your bean mass messing up your tc readings?
-Jon
Honey badger 1k, Bunn LPG-2E, Technivorm, Cimbali Max Hybrid, Vibiemme Double Domo V3
 
PaulHilgeman
Mine is spouting just like the beginning of this video:



I will try getting it right where they return to the air column.
 
jkoll42
Then I would think just off the side of the roast chamber and close to the base. You want the least influence of incoming hot air.
-Jon
Honey badger 1k, Bunn LPG-2E, Technivorm, Cimbali Max Hybrid, Vibiemme Double Domo V3
 
PaulHilgeman
thanks, will try again on a roast tonight.
 
PaulHilgeman
Alright, I give up on this with bare TCs.

I roasted two batches last night and I don't think there is a single location that gives good BMT estimations. I am afraid that if you are using a higher mass thermowell you are just watching it heat due to ambient conditions - which may parallel the BMT very well depending on your charge temp / preheat.

With a bare TC, I found good data by placing the probe right in the air stream before it enters the RC. I found this to be really useful for understanding how I was heating the beans. For example, I had been coming up on 1C at about 525 degrees, once I heard 3-4 snaps on my Ethiopian roast, I increased my ambient intake to get the temps down to about 500. The roast went right through 1C in about a minute and I was able to coast into a C+ roast about 2 minutes later with a final 30s at about 560 degrees.

Tried it in a Mokha-Java blend this morning, it was intensely layered. As the coffee cooled there was a point where it smelled like blueberry muffins, when hot it was all citrus up front and chocolate on the finish.
 
JETROASTER
Hi Paul,
You have arrived at that place.....
"you are just watching it heat due to ambient conditions - which may parallel the BMT very well depending on your charge temp / preheat."

It took me a while to accept the fact that I was only ever reading ET, but it does appear to be true.
Not to worry, eventually through trial and error you will learn the language of your machine.
My solution was/is to simply litter the entire area with thermometers, wait, watch, compare and keep some basic logs. Eventually it all makes sense, and sometimes offers some unexpected insights.
This conversation is certainly not new. Generally, the uppermost reading seems to give the best representaion of bean temp.
Good luck, and have fun. Cheers, Scott
(that Mokha-Java sounds darn tasty)
JETROASTER attached the following image:
mh_1_thermo_2.jpg
 
PaulHilgeman
The Mokha Java turned out incredible, Day 2 shows almost no blueberry, just honey/citrus up front, and LONG lingering coco / spice off the end.

I agree with your assessment completely, and I am pretty sure people that think they are watching BMT in a fluid-bed roaster simply chose a thermowell / thermocouple that has a thermal mass that shows a rise similar to that of the bean!
 
lmclaren
Hi Paul,

Take a look at ir thermometers, if you get a professional one then they have many different output modes and are quick enough to keep up with the roast. You can even calibrate some to the beans.

Check out my roaster for an example,

http://forum.home...post_38981
Edited by JackH on 02/08/2015 7:56 AM
 
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