Reading a physically moving temperature 2

[itsmoked]

I have a bean roasting application where there's a perforated rotating horizontal stainless steel drum in an oven.

Max temp is 375°F (200C)

We're trying to get the temperature of the roasting contents as it tumbles in the drum.

Easiest would be a temp transmitter inside the drum but there aren't any batteries that will put up with 200C.

Any ideas?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

The bigger issue is the fact that the probe doesn't stay in the organic product

I failed to consider that. It would (if it didn't have a 100°C case limit) be taking only a mechanical average of the beans/air temperature and I dare say it would be about 85% air temp verses 15% bean time.

Oh well.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[BrianE22]

Brian; As was mentioned above RFID craps out at a max of 150°C, too low.

The shaft would be extended out of the heated area so the RFID was in a cooler area. Maybe that's not possible for the hardware they currently have.

 

[waross]

85% air temp verses 15% bean time.

If the thermal time constant of the dial thermometer is less that 1/5 of the transit time in the beans the reading will reach the bean temperature while the probe is in the beans. Take a reading just before the probe comes out of the beans.
Does your wife have a meat thermometer with a narrow probe? Try a simple test;
Ambient at 21 degree C
100C - 21C = 79C
63% x 79C = 50C
100C - 50C = 50C
Take the thermometer at room temperature and immerse it in boiling water. The time to reach an indication of 50C will be one time constant. You need five times that to reach 99+% of the measured value.
This should let you know if you are in the ballpark for time constants with a dial type thermometer.

This is based on:

Or more simply:
1/e
Please don't think of me as irrational. grin

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!