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My second BT probe ...

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edtbjon:
I ordered a couple of 17mm thermocouplers from a German company (link here), which are the same as forum user beananimal uses in his modifications. I checked the TC's for sensible values at room temp and boiling water.
I first tried it in the original BT position, which gave me some strange readings. It was expected that the readings before charging the beans should be low, as beanamimal reported that. Now the readings were sluggish and very much off during the whole roast.
I then decided to drill an extra hole at 40mm offset, which is what Peter (beananimal) uses on his roaster. I just made a second roast with that setup, while keeping the 70mm standard BT probe in its original hole. My new TC gave the same sluggish results which you can see on the graph below. It's the black graph, "Xtra BT". (Both this and the first roast were 400g roasts.)

BTW, stainless steel is very hard...  :o My drill bit litterary melted from trying to get through the front plate. :-[ A small Dremel grinder helped me through the last bit though.

SusanJoM:
It seems that your new T/C will need a new name (there can't be two BT locations).

And it also seems as if it very smoothly follows the curves of the current BT and ET probes. 

What is the objective?

edtbjon:
The objective with this mod is to be able to get reliable readings with smaller charges. (I'm really not doing any sample roasting, as in testing a lot of different coffee samples, typically 100g/4oz to decide which to buy. But I still want to have my Huky able to do that.)
When profiling I'd like to roast say 150g and get reliable readings, which I can repeat with my full charges.
If you only do 400-500g/full pound charges, this mod shouldn't really do any big difference, but if you want to charge below 250g the size and placement of the BT probe does make a difference. (Peter "beananimal" pointed this out with his tests and videos, which we all appreciated.) The reason for the BT probe sitting as close to the center as it does is because of its length (70mm, almost 3"), while the shorter 17mm (3/4") probe can sit much closer to the edge of the drum without interfering with the flaps inside the drum.

beananimal:
Hello Björn,

I am quite surprized with that graph, especially about the sluggish behaviour.
That it goes more down after filling in the beans is plausibel for me, as it is fully in the cold beans. 

Unfortunately I used the second BT only some days on "my little fat Huky" which then was at a friends place  until few days ago.
Seeing your graph I have to do a double-check with a new additional roast next weekend to be sure that my understanding was right. Sorry for let you wait.
After that I'd upload my graphs to have a comparison with yours.

One question: To fix the probe, do you have thread in the front plate, or a nut inside the drum?

SusanJoM:
So the readings don't make sense just because of the different location?
What happens if you put the short stubby T/C in the actual BT location? 
Does it read correctly then?

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