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

 

[waross]

Temperature sensitive RFID type device?
Is there any way you can get a shot at the contents with an IR gun?
A thermo-couple inside the drum brought out to contacts outside the drum. Wipers make contact one or more times a revolution?

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

 

[waross]

How is the drum or oven heated?

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

 

[IRstuff]

What about infrared pyrometry? They can even be outside of the oven looking in.

Alternately, an imaging pyrometer might more easily show you the non-uniformity in temperature distribution. Relatively inexpensive compared to the old days.

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[itsmoked]

Bill;

Temperature sensitive RFID type device?

RFID temp sensor! Hadn't thought of that at all. Hunted them down.. 150C max. Dang!

Is there any way you can get a shot at the contents with an IR gun?

Racking my brain trying to figure out a way to do that.

A thermo-couple inside the drum brought out to contacts outside the drum. Wipers make contact one or more times a revolution?

Can T/Cs work thru slip rings??!

How is the drum or oven heated?

3phase CALRODs 230V 33A

IR;

What about infrared pyrometry? They can even be outside of the oven looking in.

That's what I've been focusing on but the problem is that even if I managed to read inside from outside it's still once removed from the INSIDE of the rotating drum.

Alternately, an imaging pyrometer

All I can think of is using a pixelated thermal imager that looks at the drum taking snapshots. The beans would be colder than the oven until they're not. Looking pixel to pixel I could find the lowest temp pixel which would be the still cool beans. Once the oven temp shifts to cooler then the beans would become the hotter pixels as seen thru the drum holes.

That would be a lot've work though.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[danw2]

For slip rings look here:

Link

I'd be inclined to the RTD version, because the cold junction issue disappears.

 

[btrueblood]

What rpm is the drum, and how long is a typical roasting cycle? Is this a permanent instrumentation of the drum or a one-off temporary setup for testing/R+D?

If not permanent: I have taken dynamic (0-5000 Hz) strain gage data from a part on a lathe rotating at up to 2000 rpm, with a strain gaged part in the chuck and the gage wires running out through the headstock. We just gave ourselves about 15 feet of slack wire and us two engineers holding the wire suspended (and letting it twist up) while the machinist made the interrupted cuts on the part, approx. 2.5 to 3 minutes of run time. Between tests, we would have him reverse the lathe to un-twist the wire.

If permanent: A high-ohm RTD probe might give a stronger signal (less noise from the slip rings) than a thermocouple, and be more stable over the long term. You should be able to get platinum RTD's in the 1k-ohm range fairly cheaply, and in nice stainless steel sheaths that can be clamped or tack welded onto the drum walls. Better, but possibly bulkier, run the wires for the RTD's up and into a hollow shaft for the drum, then down the shaft and outside the oven to a place that is cool or can be cooled, then connect where you have RTD transmitters (attached to and rotating with the shaft) that shift the signal to 4-20ma prior to passing through slip rings to your recording instrument.

Lastly, a bit more experimental...but...we used to take temperature readings of an operating rocket thruster nozzle in a vacuum chamber using an optical pyrometer. Because of the layout of equipment, and the fact that you really don't want direct or even <90 degreee impingement of the hot gasses on a (even quartz) window, we had to use a mirror to reflect the image of the nozzle back to the pyrometer, roughly 150 degrees of optical path bending. We did some calibration work to see what difference the mirror made - it was minimal for our purposes and easily calibrated out. So...put a mirror canted at 45 degrees along the axis of the drum, and "look" at the drum walls with the ir gun or pyrometer looking down the axis. Calibrate the gun by sticking a test block (suitably heated and instrumented) in the drum whilst static. In your case, you will want to be able to access the mirror to clean it regularly (don't know, but suspect roasting coffee beans give off a lot of smut and oils that might occlude the mirror over time), and possibly to recalibrate after a roasting cycle and before cleaning so you could get an idea of how much the signal drifted during the roasting process.

R+D baby! Have fun.

 

[EdStainless]

How long does the roasting cycle last? I have sent TC loggers through furnaces at 1500F.
Sealed boxes with lots of good insulation.
Maybe clip one to a fin inside during a run?

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P.E. Metallurgy, consulting work welcomed

 

[3DDave]

Time for either the smallest wax motor or finding a material with a curie temp in this range. Perhaps a tiny bi-metal device the size of a bean. The wax motor and bi-metal device could be linked to a variable air-transformer that would change the response frequency to an mm-wave RF pulse. Not sure there is a coffee bean size off the shelf transponder.

It seems like the difficult problem is to measure the temp of the beans and not the air or the rotating drum.

Perhaps sampling? Drop a bean like a bingo/lottery ball and take it's temp shortly after it leaves. The drum could have a pocket added that only opened at a certain rotation position.

 

[MacGyverS2000]

If this is a more permanent installation, I would think a probe placed somewhere along the shaft would be useful... doesn't need to rotate with the drum, but it would definitely be on the inside of the oven.

If you want the temp of the actual contents (and not just overall oven itself), a well-aimed pyrometer is probably the only way to go.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[btrueblood]

If you just want the max. temperature, take a bunch of beans and coat them with temperature-sensitive paints of various ranges - see:

https://markal.com/products/tempilaq-advanced-2

It looks like they have temperature indicators at 25 deg. F increments around 375 F, implying a precision of about 10~15 F.

Of course, the paint may wear/rub off of the surface of the bean in tumbling. May have to make a set of R+D beans, with recessed pockets to hold the paint...this could require tooling jigs for machining paint pockets in coffee beans, and some 3-axis milling machine CAM coding... Or, maybe make bean simulators from wood or ceramic, so they are more durable and could be re-used.

 

[btrueblood]

One last thing, I promise...

Does the drum shaft have to go completely through the drum? Could the end bearings not be cantilevered? If they could, there is an easy path through the non-driven end by making the shaft hollow, and passing a fixed (non rotating) probe through that end. It may get beaten up by rotating into/out of the beans as they tumble...but maybe if the probe is built stoutly enough it could hold up.

 

[TugboatEng]

Here is an example of temperature measurement through slip rings.

Picture is from this link.

https://www.google.com/url?sa=t&sou...oQFnoECAMQAg&usg=AOvVaw2mCcW6gZCZ8QqXWpIFsX0X

 

[BrianE22]

Does the center shaft spin?

 

[waross]

My thought was to investigate RFID technologies and then roll your own with high temperature components.
You may mount your circuit on the outside of the drum with only the probe on the inside.
I am guessing that the beans are a tumbling layer in the bottom portion of the drum.
You could power the device with an RF field and take trend readings as the device was in the lower part of the cycle and immersed in the beans.

For the slip ring idea, I wasn't thinking slip rings.
I visualized metal contacts about an inch or two long, mounted on the exterior of the drum.
Stationary would be small wheels that would make about 240 degrees of rotation as they were contacted by and turned by the contacts on the drum.
Once clear of the drum contacts a spring would return them to a stop. They could be jumper connected with a flexible jumper.
The axis wheels could be inclined slightly to the axis of the drum to give a slight scrubbing action to keep the surfaces clean.

Is this a batch operation or a continuous operation?
Is the drum supported by a bearing at each end?
Is it possible to modify the drum in any way?

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

 

[itsmoked]

danw2; Nice. We'll have to consider this. May be too thick but it might work.
Totally with you on the RTD angle.

btrue; RPM is what you'd see in a meat rotisserie. Maybe 2RPM?
Roasting cycle is about an hour and change.

We want to rest control onto the beans instead of dead reckoned outside the drum air temp and fixed time.

into a hollow shaft for the drum, then down the shaft and outside the oven to a place that is cool or can be cooled

I think this is where we'll have to go. Currently one end of the shaft is gear driven and very technical to get through, like center drilling the 90 degree gearbox shaft. But the non-driven side, while solid, isn't doing much of anything. I think that can be re-tooled to make the center hollow allowing a completely non-rotating solution to present itself.

Yeah an IR mirror! Perhaps a truncated-cone so only the lower edge would be viewed by the thermal imager which would only take the bottom-of-the-drum temperature where the beans will always be..


EdStainless; Yes! We used to do the same thing with rocket fuel mixers and sterilization chambers. Insulate and thermal mass the logger and toss it in. Unfortunately this is a production system that runs about 3 batches over 4 hours and will eventually be longer runs in 7 ovens so I see keeping track of probably 30 thermal loggers with batteries charged and in order as unworkable. They'd also need to get the data out as we need the data realtime to control the roasts.

3DDave; LOL. Crazy waxmotorbean! In about an hour it would probably look like a bean and one would eventually go down process.
I was trying to come up with a bean sampler too! Nasty mechanics.

MacGyverS2000; Permanent installation, yes. It would need to NOT rotate so the bean pile at the bottom of the drum is what's being monitored. They sort of slither up the side 90° then fold-over and slide to the bottom again.

btrue; Not going to work because it turns out the beans come in all sizes and fore instance smaller beans take longer to heat than larger ones because of the resulting interstitial air spaces (the heating medium -air) can't get between them to heat them up. Also a different weight batch shifts everything. Too many variables to do any characterization.

Yay the hollow shaft angle. That's where this looks like it's going. You saying "cantilevered" made me think of actually sitting one end of the drum on two bearings so there is nothing going on with the axle at all. It could be a 4 inch hole! The beans can't get up to the axis ever... hmmm.

Tug; Gadzooks!

Bill; Batch. Any electronics including the ones to make an RF powered simple device would probably have thermal diffusion lifetime problems. Also to drive the RF would require dealing with acres of SS sheetmetal wrappings. Ugh.

Bearings on the ends which had been the chicken rotisserie support system providing three chicken shafts. The drums are custom designed and made so they could be changed. I'm hoping only one exists at this time.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[BrianE22]

Too bad the shaft is rotating. If they have the room maybe they can convert is to a stationary shaft. It might be cheaper than a thermocouple slip ring or pyrometer.

3DDave's idea might still work with a rotating shaft. Put a hole in it and a stationary auger. Let out a dozen or so beans into an insulated container and quickly measure the temperature. I know, a little too Rube Goldberg.

 

[3DDave]

The mechanics aren't too tough. Put a small hole in the side of the container with a little door/catch on it - look at marble traps on marble machine/sculptures. Release the bean with a small lever that is moved to press it open when it's even with the axle so the other beans don't spill out. As the drum turns an unselected bean will fall out back into the moving pile anyway and a different bean will drop in on the next cycle - that way the bean is not permanently trapped.

Plenty of marble pick-up mechanisms to choose from.

 

[waross]

Forget my other suggestions. I am tending towards the hollow shaft solution.
How about replacing the NDE shaft with a 4" stainless pipe centered and supported by three cam followers?

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

 

[Compositepro]

If the roaster is well designed, with good air flow though the beans, there is little benefit to reading the actual bean temperature. Reading the air temperature after it has passed through the tumbling beans will be just as useful. When the heaters are at full power there will be a large delta T between the inlet and outlet temperature of the air. As the beans heat up to oven temperature, the heater power will reduce to a low level and the beans will approach air temperature.

It's like boiling eggs, is there any benefit to knowing the egg temperature? There is a large difference between the center and surface. The same with beans. What is needed is a consistent and repeatable process.