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

 

[Pud]

As Compositpro said

I come from the plastics industry where drying plastics is critical to end part performance.

All the (modern vacuum) dryers I have ever used always monitored the outlet temperature of the bulk material. Most had the drying time started when the outlet temperature reached the inputted value.


Politicians like to panic, they need activity. It is their substitute for achievement.

 

[3DDave]

The question for sensing the air temp is whether the roasting process is converting a large amount of the energy into some transformation process. Certainly forcing water to evaporate is one of those conversions. It helps if that transformation is below the temp of any other transformation - the melting point of plastic, for example.

Are the beans being dehydrated or is there some process akin to caramelizing that doesn't see such a large shift or may even be an accelerant? For example, if the beans were to darken then they may absorb IR more readily, causing a runaway where they absorb more until they are charcoal.

 

[itsmoked]

Compositepro; This is a converted chicken roaster (many of them). So NO not "well designed". Also NOT a continuous process. Batches of all sizes, moistures, initial temperatures, and mass. The air doesn't pass anywhere although a little is sucked in around the non-drive bearing shaft and blown out the other side around the drive side. Unlike boiling eggs the heating medium is no where near as thermally dense.

Pud; This thing is more like cooking the beans not drying them.

3DDave; Nothing so odd as an endothermic type result.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

Bill; I like the cam follower. Unfortunately all I find would cause bad geometry issues because they tend to be thick and with long studs.

Cam followers would force the support shaft to be way too long blocking the view to the bottom of the roasting drum.

Looking for a Flange Mount Bearing is causing the same dang problem because any that have a 2" ID, helping the non-contact T/C get the angle to see the bottom, expect to support thousands of pounds and so have extremely wide bearings.

Anyone have a thin idea?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[3DDave]

Would the cam followers not be used on the rim of the drum and be outside the perimeter?

 

[Compositepro]

It makes one wonder why no one else is roasting coffee beans in a chicken roaster. All you need is the right thermometer.

Adding a blower in the oven would be a far better improvement than any other.

 

[3DDave]

It's for chicken finger coffee. New market. Unlimited growth potential.

 

[itsmoked]

Would the cam followers not be used on the rim of the drum and be outside the perimeter?

Hadn't considered that. See the picture of the rim above. Think it would work?


Comp; Actually many use these ovens converted just like this for roasting. The guy I'm working with has used this thing for more than a year. Regular roasters are 10x more expensive and operate like a flying a plane, requiring a skilled operator. This thing works okay being run by any employee after seeing it run and 5 minutes of instruction.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

My thought was that the center shaft be removed. The drive end bearing and the shaft support may need to be modified.
The Non-drive end shaft would be replaced with a large diameter tube supported by cam followers.
Or
The entire drum could be supported at the non-drive end by cam followers similar to a clothes drier drum or a front loading washer drum.
Size and weight is no object. Think large transit mix concrete truck.

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

 

[itsmoked]

Bill; Yeah, I got all that. The problem is that high temp cam followers are a hundreds apiece and we'd need three per roaster. Next, they all come on absurdly long studs without any threads for half their length. This either has them crowding the drum end or if we go with normal temp and mount them on the outside wall pointing away from the heated space they'd require a reeeeeally long axle tube. Night as well go with a flange bearing at that point.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

How about this..

Given the drum is like this.

Cut a single hole in the side of the oven.
Mount a non-contact T/C in the hole looking at the side of the drum just above the end spider outer ring.
Mount it so it sees the three spider bars as they pass in front of it but otherwise see's the beans thru the perforations just above the ring.

This sensor has a 350ms response time. I should be able to see the oven temperature looking at the spider arms VERSES the bean temperature when the spider arms are elsewhere.

The difference between the two will show the difference between the beans and the oven itself.




Keith Cress
kcress -

http://www.flaminsystems.com

 

[danw2]

I like that idea of comparing the spider arm temp to the perforated steel/product temp.

I don't follow the IR market so I don't know if that Raytek temp sensor is a wideband, linear 4-20mA model or whether Raytek has adopted a line of the cheaper units that are a thermocouple thermopile with a bowed response over some relatively specific, narrow temperature range and which expect a T/C analog input with CJ compensation (like an Exergen non-contact sensor).

When screen is passing by, the IR will 'see' a signal that is the combination of the relatively low emissivity heat emitted from the perforated steel and the relatively high amount of emitted from the product and when the spider arm passes the signal will be the low level emitted heat of the steel, biasing the reading toward the organic, but on the low side because of the steel contribution.

The linear IR's always have an emissivity adjustment and my memory from years ago recalls that 'back when' the Exergen thermopiles expect the AI to do an offset for emissivity. Assume you use adjust to a higher emissivity to read the organics.

If the exterior steel is all clean and shiny, it wouldn't surprise me if the spider arm temperature was perceived/indicated as a lower temperature than the organic product because organics typically have high emissivity, so they emit more heat than the steel and the sensor emissivity is set high. If any of the steel is dirty, then high emissivity dirt affects the reading. Spray painting the spider arm flat black (automotive exhaust spray paint) will make the spider arm steel high emissivity and get you close to the actual steel drum temperature. I think you'd want shiny perforated steel to reduce the contribution of low emissivity perforated steel heat and maximize the contribution of organic product heat to the sensor.

Field calibrate the temperature reading by stopping the drum, inserting an RTD hand probe and taking an reading to determine your 'real' temperature and either tweaking the emissivity adjustment (don't let the operators see you do it and glyptol the adjustment screw when you're done) or add the difference between reported and real as an offset in the temp indicator.

 

[waross]

And I just remembered another condition.
Working on freezer conveyors we had to use edible lubricants. I am not sure how that would work at high temperatures.

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

 

[btrueblood]

Well, if the IR sensor can read "through" the mesh, then why not put it on the side or perhaps at 45 degrees below the axis, and aiming at the cylindrical wall? For that matter, you could have an array of them aiming at different locations along the length of the drum, and at various elevations above bottom-dead-center. Wondering if there is a good IR-transparent material you could embed at various points along the mesh...how toxic is gallium arsenide...hmm...

 

[BrianE22]

Are there any RFID devices that can condition or interface with a temperature measuring device? Use the RFID as a slip ring assembly. So temperature probe attached to rotating shaft, wires out center bore in shaft to rotating RFID on outside of heated basket.

 

[analogkid2digitalman]

Old school low tech- dial/probe thermometer?

https://www.grainger.com/product/46...VWRmtBh1YLAoSEAQYASABEgJp7vD_BwE&gclsrc=aw.ds

EDITED- Did not realize it was 200C so beyond the range of meat thermometers, added a link above

-AK2DM

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"It's the questions that drive us"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

[itsmoked]

danw2; I just grabbed an example non-contact T/C for illustration. Raytek has a dozen different models and there are about 6 different companies that make them. You can get every kind of output you can think of so I suspect I can find one that will be sufficient. I like this one as I can use a meter and a simple hole in sheetmetal and try it to see what happens. A completely different job than having to come up with a different bearing system for the drum. If the $200 probe doesn't work a screw and a little square of sheetmetal repairs the test modification.

Paint in service like this is verboten. It'll have to work without or a piece of black anodized aluminum will have to be used instead.

I'll float this by the guy and see if he want to "do the study".

Thanks for the emissivity thoughts. I hadn't considered that looking at the spider could actually give a lower reading but it could!

The new drum he's working on has MUCH larger hole sizes which should probably help this whole scheme.

Bill; Anything in the food path needs "food consideration" for shore. Paint is generally BAD an screws and nuts that can land in the food are also very bad.

btrueblood; I'd like to use several but they ain't cheap and in this case it's all X8 so I have to be somewhat conservative. There are also simple physical constraints. For instance it would a problem to try to have the sensor point up from the bottom. The sensor would require raising the entire oven the sensor length and most of these ovens are already double stacked. Ugh. Also NCT/Cs have like a 4:1 viewing ratio. For every inch away the width of the view greatly increases so it's seeing a larger and larger region.

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


analogkid2digitalman; Damn! That's outta the box. If the entire thing can sustain 200C then with it screwed into the drum one could simply photo the dial and do video comparisons to read the dial. Interesting. LOL .


Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

I like AK2DM's suggestion.
Read the probe optically just before if exits the beans as the drum rotates.
Use a "sample and hold" circuit to update the bean temperature signal once per drum revolution.

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

 

[danw2]

You need to watch for the case temperature limit for the bimetallic thermometer (old school low tech). Wika limit is 200 DegF:

and it's likely that other manufacturers' specs are around that same number.

But could you put the probe through a flat sheet of aluminum or SS shield to prevent radiant heat from getting to the case/dial assembly in order to keep the case temperature down? Conductive heat through the probe would be minimal.

The bigger issue is the fact that the probe doesn't stay in the organic product, no matter where you install it, the probe rotates in and out of the product and spends a good portion of the rotation in the air, not the product. If the IR concept is feasible, the IR could be aimed at the lower section where gravity is going to keep a pile of the organic product.

 

[waross]

I remember trouble shooting an instrument that measured the height of molten glass in a glass furnace.
A probe was lowered mechanically until the tip of the probe touched the surface of the molten glass.
That completed a circuit that stopped the mechanism, read the position of the mechanism, froze the reading and sent it to a PID controller on the feed system and then returned to the top of the stroke.
The cycle repeated continuously. If the glass level was rising or falling, the signal would be updated and the PID would react accordingly.
Will the temperature of the beans change enough from one revolution to the next to introduce significant errors?
If so, use three or four dial thermometers.
(Molten glass is a conductor of electricity and a circuit was completed through the mass of the molten glass.
Another industry, another glass furnace. This one was heated by passing an electric current through the molten glass.
At startup, the glass was first melted with gas heaters and then the electric resistance heat took over.)

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