I have installed another bean temperature probe in the position of the left screw of the glass window. This position "BT2" is near the bottom of the drum and can be fully submerged inside the beans to have a better approximation of bean temperature than the "original" BT probe position in M3. I have posted the Artisan chart with 4 probes measurement of temperature using TC4.



What is worth mentioning is the difference between the original (BT-blue) and new (BT2-green) after the 1st crack, the BT measure is still rising whereas BT2 is becoming flat and rise slowly. If we use the original BT for measurement and try to lower the power towards the end of the roast, the actual bean temperature may become flat or dropping even in the chat showing "BT" is still rising slowly hence "baking".



The BT2 probe screw size is M4 and length of the TC sensor is 2.5cm without hitting by the rotating fin inside the drum.

Alex

Thanks, Alex. I've been toying with the idea of putting a BT probe in the exact same spot. Now the trick is to find a thermocouple probe that can fit.

The difference in temperature between BT and BT2 is larger than I would've hoped to see.

Any issues with the thermocouple being in the way when you drop the roast into the cooling tray?

The actual length of the the TC senor is 3cm with 2.5 cm after the door and it does not hit the drum when open the drop door.

Alex,

This is a cool mod, I had pondered how to get a TC in that spot before, nice solution you implmented.

Would you mind letting me know where you got your TC, and describing the install process a little more, I would love to copy this setup.

Jeremy

Thanks for the Artisan snapshot Alex! It really says a lot! I have my probe inside the bean mass, similar to the spot you use now. What I did was use the original hole for the bean temp probe, but instead of putting a probe in there I basically put a metal post(one that I could bend down into the bean mass). Then I wrap a bare thermocouple around the post, so it stays in position. I run the wire up threw the chimney, and out one of the chimney screw holes.

My BT probe from erics is simply bent so that it lays directly in the center of the bean mass.

I've also pulled out my ET probe and am going without it. I never really made decisions or changes in the roast based on it, so it was only visual clutter in my opinion.

Alex, I second your findings and I think you've nailed the problem with the original BT probe placement. The way the original BT probe record temperature, relies on the frequency of the beans dropping onto the probe. At the time near 1C, the beans are expanding and volume is increasing. In terms of density, it was dropping all the way towards and after 1C. With a decreasing density of bean mass hitting the original BT probe, you can expect less contact have been made by the beans on the probe. As such, the original BT readings were contributed by an increased portion of drum air than the beans themselves towards 1C/2C, meaning that the readings are much less accurate and much dampened by the drum air temperature.

I think your BT2 readings had reflected more of the true bean temperature. The lower thermal mass associated with your BT2 probe had also helped to make it much more responsive to temperature change. Note BT2 had recorded a much lower turnaround temperature than BT1. It proved how much better it had recorded the actual bean temperature.

Few photos on the installation of BT2

M4x6 screw


Replace the original screw


Insert the 3cm thermocouple

Alex,

Great, excited to get this over to Macau and get it installed on my M3!

Jeremy

If you own a drill press, here's a nifty trick to drill a centered hole in the original screw. I've done it for my MET probe and it works well, but takes a bit more finesse with lower-end drill presses.

Alex,
do you happen to know the diameter of the thermocouple probe that you're using?