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Homeroasters.org » BUILDING A ROASTER » Fluidbed Roaster
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500g (hopefully) fluidbed roaster
JackH
Could one of the probe wires be picking up noise from a motor or fan? The TC4 has sensitive inputs. Check your wire routing.
---Jack

KKTO Roaster.
 
RedAce
I did a control measurement today with a standalone thermometer - it behaved the same so I really think the issue is not in the wiring. Humidity/preasure or something of that sort is still basically the only reason I can think of.
During one of the roasts, my chaff colector fell down from the roaster and I noticed similar spikes/drops in ET as I tried to put it back on top. And since the caff collector restricts the air outflow it led me to the conclusion that it is caused by some preasure changes or vapor escaping the beans...
 
allenb
renatoa wrote:

I doubt that a power change has such instant effect...
After TP the ET in my oven can't raise more rapidly than 80C / minute... and when I cut power in final stage of development, the drop is about 1 degree every 5-10 seconds.


In a fluidbed roaster, ET is the heated air stream entering the roast chamber and can be changed quickly compared to the environmental temperature of a drum or in your case a TO which requires changing the temperature of a large volume of air plus the effects of the air being in contact with the enclosure plus contents.

All of the electrically heated fluidbed roasters I've used can raise and lower the temperature of the air stream as much as 100 degrees F in a matter of a few seconds.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
allenb
RedAce wrote:

I did a control measurement today with a standalone thermometer - it behaved the same so I really think the issue is not in the wiring. Humidity/preasure or something of that sort is still basically the only reason I can think of.
During one of the roasts, my chaff colector fell down from the roaster and I noticed similar spikes/drops in ET as I tried to put it back on top. And since the caff collector restricts the air outflow it led me to the conclusion that it is caused by some preasure changes or vapor escaping the beans...


Now that you mention it, I had a similar experience with a fluidbed that had a nasty habit of popping it's chaff collector/lid assembly upward just enough to allow a higher air flow through the roast chamber with subsequent drop in the entering air stream temperature. I wonder if there is a temperature related event that happens during each roast where just the opposite is happening with something causing an air flow restriction at a temperature you hit at end of drying?

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
RedAce
I get that ET in a fluidbed is very sensitive and can change rapidly based on heating output, airflow, preasure etc. And if the spike was only in ET I would be fine with that.

But the actual BT simply cannot change this fast and based on the FC and DROP temps, the reading is accurate in the second part of the roast. But SOMETHING is lowering the BT reading in the first part of the roast and disappears quickly around the 120°C mark. And I cannot think of anything else than vapor escaping the beans that could have such behaviour. But why would my roaster be the only one encountering this?
 
chaff
Hi !
After substituting thermometers I'd be pretty convinced the measured temps are accurate and
you've already had a glass chamber crack as a gap closes under expansion. Too, the beans start to jump around more at that stage suggesting there's less resistance to airflow from the beans proper.
If a jump in heating output can be eliminated, perhaps with the help of a low-wattage lamp across the heater's input, could the ET thermocouple be used as a 'sniffer' around the roast chamber to detect any hot air leaking during the roast ?
 
RedAce
I have done some sciencing today and finally found the cause (and sollution). It´s probably no surprise, that allenb was right claiming, that it is probably real BT/ET rise caused by high heat and not an artifact. The fact that it was always happening at the same time confused me so much I started looking for some sophisticated reason and did not look into my first suspect - the faulty dimmer.
As I was roasting some navy beans today (BTW did you know that they roast very similar to Panama and even have sort of a First Crack? Grin ) I got a spike again at the 5 minute mark. But since I was roasting navy beans and not some expensive coffee and was in an experimenting mode I wanted to crank the heat up to max to see how fast the BT can really rise. So I did it and... nothing happened. So I dialed it all the way down and... nothing happened. The BT was still rising at the usuall rate.
At that moment it hit me. My controls are enclosed in a wooden cigar box with no real ventilation (I guess most of you already know the cause by now as well) so as the roast progressed, the dimmer got hotter and hotter until (around the 4-5 minute mark) it was like "F#!k this s#!t, I´m too hot and sick of regulating your heat." and it sent full power to the heater. And as I cooled the beans after the roast, it cooled as well and was ready for another 5 minutes of glory with the next batch.
So I tried to open the box today and cool it with a PC fan and... IT WORKED. Full control during the whole roast and no spikes. Now it´s ready for the TC4 PID control which I cannot get to work but that is story for another day Grin
Thanks all of you for the input and for pointing me in the right direction.
 
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