Thermocouple Placement for Accurate Profiles?

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
WilliamB

#1: Post by WilliamB »

Hi all,

I've noticed that thermocouple placement for coffee roasters seem inconsistent. The BT probe tends to be in the main mass of the beans (bottom left of the drum), but it seems that the ET probe tends to vary. MCR puts there in the top right quadrant of the drum, while others put it up on the dropper chute, and others put theirs further down on the exhaust line. Further, some machines have ambient temp sensors and other temps available.

I'm looking to add some thermocouples to an older Diedrich I recently purchased. I'm curious if anyone has experience with these placements and can chime in. I'm probably most inclined to go with the MCR method, since that would provide the most accurate heat of the inside of the drum vs. the bean temperature. I'm also wondering, does anyone recommend having thermocouples other than the BT & ET sensors?

Further, are there any other Phidget sensors worth looking into (air pressure, humidity, etc.) that would integrate well with Artisan that you would recommend?

Thank you for your time.

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CarefreeBuzzBuzz
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#2: Post by CarefreeBuzzBuzz »

BT placement depends on drum rotation direction.
MCR puts their ET in the drum, and you could have another in the exhaust somewhere if you think you would use it. What does Diedrich normally use on whatever size you got on their new machines.
I recommend RTDs for probes and once you get a VintHub the rest of the ambient sensors are cheap.
If you want the doc I did when I upgraded my MCR 500 send me your email in a PM.
CarefreeBuzzBuzz
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RusticR

#3: Post by RusticR »

I'd recommend in this order:

2.5 - 3 mm probes
Intake air probe (my MCR is directly above the back axle carrier)
BT low in the drop door (I added a second (lower) probe and can avg the two BT in Artisan)

WilliamB

#4: Post by WilliamB » replying to RusticR »

I've never heard of averaging BT's. That's extremely interesting, and I may look into doing the same.

There's a set available that offers a pretty much everything you're talking about minus the Intake Air Probe. What benefits are there to this probe? I could see where it may be helpful but I struggle to understand its utility over simply recognizing how hot/cold weather and air temps slightly affect how much gas you need.

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CarefreeBuzzBuzz
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#5: Post by CarefreeBuzzBuzz »

With virtual devices you can use mathematical formulas.
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ballpencil

#6: Post by ballpencil »

WilliamB wrote:I've never heard of averaging BT's. That's extremely interesting, and I may look into doing the same.

There's a set available that offers a pretty much everything you're talking about minus the Intake Air Probe. What benefits are there to this probe? I could see where it may be helpful but I struggle to understand its utility over simply recognizing how hot/cold weather and air temps slightly affect how much gas you need.
I prefer intake air probe to the typical placement of ET. To me it's closer to what BT will strive to reach, and it actually is for the case of truly convective roaster. For your classic drum roaster on which the drum is still heated by flame, we need another probe which is Inner Drum Surface Temp. The interplay between convective and conductive heating shown by these two probes are the actual driving energy for BT.

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Almico
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#7: Post by Almico »

I have an ET probe in a chimney bolt hole on the faceplate away from the bean mass. It measures the air temp in the drum. That air temp is a mixture of the air temp coming in and the temp of the beam mass in the drum.

I have a BT probe 2.5cm from the drum wall at 8 o'clock on the faceplate with a cw spinning drum. I can get good data with with 1# of coffee in a 10# drum.

I have an intake probe behind the drum that measures the air temp before it enters the drum. This is useful when adjusting the airflow mid-roast. I want to know if inceasing air is going to raise the ET or lower it.

Placement of the intake probe is critical for my purpose. If I put it high in the roaster, towards the roof panel, it will measure over 800*F. Towards the bottom it will measure 400 under the same conditions because it will pick up the ambient air. It needs to be in a location where it will tell me when incoming air matches ET in the drum.

WilliamB

#8: Post by WilliamB » replying to Almico »

This seems like a great idea. I have to imagine that this intake probe would need to be significantly more responsive, perhaps even a naked thermocouple? That way you could quickly decide if you're pushing temperatures the wrong way.

I could see where an interplay of an intake, ET, and BT would all be incredibly helpful, especially at crash and flick mitigation. I would imagine that one could calculate some % intake temperature change needed to fully mitigate those two factors via airflow adjustments.

I appreciate you saying that you use the chimney bolt hole. I hadn't thought of that, and that seems like it would work wonderfully on my machine (I'll double check clearances). Now, I saw you said that you can get good "data" at 1#. Does this mean you find yourself capable of doing 1# roasts at sufficient quality?

N3Roaster

#9: Post by N3Roaster »

Specifically for a Diedrich roaster, when they've included the 2nd probe that goes in through the side of the chute the hopper connects to, under the door mechanism with a 90° turn into the drum space. That part can be unbolted on mine so the modification is relatively simple. Because of how the airflow on that machine works, what you're getting there is a good read on the temperature of the air going into the drum before it's had a chance to interact with the coffee, which I generally prefer over an exhaust reading. I've modified my IR-12 (built circa 2000) to include that, got the probe and the mounting hardware from Diedrich. Once you learn how to read the data coming in on that it helps a lot with making precise control adjustments for staying on plan. The difference between your intake and bean temperatures is useful, but if the data is being graphed sensibly I'm not convinced there's much advantage to having that difference calculated as a separate data series.

Regarding other sensors, I can't speak to Artisan specifically, but lately I've been working with a prototype for a new kind of live degree of roast analyzer that gets me information on how dark the surface of the coffee is throughout the roast. That device is driving a 4-20mA current loop that I'm reading from a Phidgets DAQ_1400_0. I can't say how useful that is yet (I've been modifying the code on the device to see if I can improve its performance) and this specific thing isn't a real product yet (there are competing products that work on different principles, no clue what their logging interfaces looks like), but so far I've pulled out some interesting observations that I need to dig into and see if there's something useful to those.

WilliamB

#10: Post by WilliamB »

N3Roaster wrote:Specifically for a Diedrich roaster, when they've included the 2nd probe that goes in through the side of the chute the hopper connects to, under the door mechanism with a 90° turn into the drum space. That part can be unbolted on mine so the modification is relatively simple. Because of how the airflow on that machine works, what you're getting there is a good read on the temperature of the air going into the drum before it's had a chance to interact with the coffee, which I generally prefer over an exhaust reading. I've modified my IR-12 (built circa 2000) to include that, got the probe and the mounting hardware from Diedrich.
When I went in to roast today, I double checked some of the recommendations here. It seems that the chute's mounting screws to the faceplate do indeed go all of the way through to the inside of the drum, and would give me about 2 1/2 - 3" of clearance for a thermocouple before it would catch on a blade on the inside. I think for now that commandeering this hole for the sake of mounting an ET thermocouple would prove beneficial.

For the configuration you're speaking on, are you saying that the thermocouple would be drilled into the side of the chute? Meaning, the length thermocouple is running parallel with the faceplate of the roaster? If I have trouble mounting the thermocouples in the existing drill hole, I may go with you recommendation if I am understanding you properly. But before I do that, I would like to avoid as many drill holes as possible.