Homeroasters - Home Roasting Coffee Community » BUILDING A ROASTER » Fluidbed Roaster
Who is here? 1 guest(s)
Page 2 of 2: 12
 Print Thread
Is vacuum cleaner motor ok for fb roaster?
renatoa
Top  #26 Print Post
Posted on 04/02/2023 12:58 AM
Could be also a calibration issue, if the measurement system is not factory calibrated.

If a very low voltage and high precision voltmeter is available, voltage measurement directly on the TC should read about 8.2mV at 200C, for a quick check.
 
walk
Top  #27 Print Post
Posted on 04/02/2023 1:32 AM
A higher temperature would be much easier to understand. I would really like to understand how a lower temperature can be shown. The effect of a relatively massive device body (stainless cone, 5mm glass tube)?

I connected another reliable one side by side as a check and got the same result.

Used probe: K-Type Thermocouple 1.5mm x 50mm

https://www.aliex...1802mjTrhP
Edited by renatoa on 04/02/2023 2:09 AM
 
renatoa
Top  #28 Print Post
Posted on 04/02/2023 3:42 AM
Maybe the junction was wrong mounted inside the sheath... in the middle, at 25mm from the tip, instead closer to tip.

Can be easily checked, just pinch with two fingertips various sections of the probe sheath, and watch the rate of rise, the maximum is about 1 cm around the junction.

If this is the case, the most active area of the TC could be shadowed by the funnel.
 
walk
Top  #29 Print Post
Posted on 04/02/2023 9:44 AM
Thank you. I'll let you know if I find anything.

I have a lot of conflicting thoughts regarding temperature measurement and pid control. I have compared different TC's in previous drum roaster BT operation. The thicker the TC, the longer the delay associated with the delta. Even the 1.5mm TC seems too slow to me in this context. After the heating element, I installed this type:

https://www.aliex...y9wWXQOLN3
It even draw SSR switches. In the drum I used a similar 3mm TC next to it, it was interesting to see the differences.
Edited by allenb on 04/02/2023 10:29 AM
 
renatoa
Top  #30 Print Post
Posted on 04/02/2023 10:46 AM
Not sure what are your realistic expectations about the TC response time, anything under 6 seconds is fast enough for a single digit measurement system.
A TC hosted in a 3 mm SS, or 4mm brass sheath has about 3-4 seconds lag in the step response test, which is more than enough.
The naked junction from the link above is way too noisy in real world, if exposed as is to air or beans. Usualy, for air measurements they are hosted in a flute style sheath, i.e perforated pipe, like the attached image
~~~
renatoa attached the following image:
8716-air-gas-probe-zoom.jpg
 
allenb
Top  #31 Print Post
Posted on 04/02/2023 10:52 AM
Depending on many factors, many sheathed probes, when extending less than 3" beyond it's entry point, will conduct too much heat to the bulkhead attachment nut giving it a false low read. I had this happen using a stainless steel sheathed TC that extended 2" into the bean bed on a drum roaster. These work fine for liquids but not so good for air.
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
walk
Top  #32 Print Post
Posted on 04/04/2023 12:48 AM
The probe has been checked, it works properly. Would suggest that the deceptively low temperature is the reality. The beans circulate and the sensor is located at the end of the cycle. The missing degrees are transferred from the surface of the beans to the chamber body. A thermos type chamber with low mass would be good to avoid this.
Since the given temperature may not be the same every roasting time, I have to lift the probe towards the beginning of the return path of the beans, i.e. higher.
Edited by walk on 04/04/2023 12:25 PM
 
walk
Top  #33 Print Post
Posted on 04/04/2023 4:00 AM
180C and 205C Drops
walk attached the following image:
180c_and_205c_drop.jpg
 
renatoa
Top  #34 Print Post
Posted on 04/04/2023 11:54 AM
Well, you can live with it, actually the variations are more important than absolute values.
A value of 7 degrees per minute for RoR will have the same meaning even if it is the 180-187 interval or 195-202...

Or, you can simply add a gain factor to your TC processing code, to make 180 read as 200 C.
We live in a deep fake world, after all... Grin
 
walk
Top  #35 Print Post
Posted on 04/17/2023 11:22 PM
I replaced the BT sensor with a 5cm longer one and the temperatures became as expected, fine-tuning still takes time. With a non-operating roaster and 250 g of green beans, the tip of the sensor is placed under the top layer of coffee beans. The first results seemed quite correct, there seem to be problems with hearing the cracks.
 
Page 2 of 2: 12
Jump to Forum: