Thank you all for your feedback.

I've finally put my order in at Omega.ca yesterday. I went with two XCIB-K163 probes and bought a HH806AU data logger. I will have to wait two weeks for my order to ship as I also bought a custom order probe... for cooking: I'm tired of these $10 meat digital thermometer that fail after six months (we are probably on our fifth).

I'll report once installed. Ideally I want to fit them in a non permanent manner, to recalibrate, reposition them, etc. I would therefore avoid JB-weld or such. John's solution seems like a good idea. I'll need to see if I can buy appropriately sized bushings at my hardware store. And figure how to "clamp" the wires so to ensure the T/C tip stays in place.

I just stumbled on this post by rama. It shows very clearly where the beans are when tumbling:

rama wrote:
[...]
The BT installation location was chosen by the very obvious "clean" spot the beans scrape away at the rear wall.

PS. My order from omega.ca arrived today.

FWIW, here is the location of the K-probe in the current (newest) KN-8828B models.

Randy,

Thanks for the picture. Using a stem sensor is certainly a good idea, instead of the flat one on mine.

In this position it would be just above the moving beans.

ASAIK, the previous version (i.e. mine) had a RTD sensor, so this would also be a change toward a thermocouple.

JohnB. wrote:It's nice that they finally replaced the "in the wall" sensor but that is an odd position for the new K type probe. Too high for BT & too low for accurate ET.

This.

The position is... baffling.

I can only guess why it is there - It actually is in the bean mass for the entire roast from what I could tell (250 gram mass of beans). Not terribly deep in it at the beginning, but in in nonetheless. The old thermocouple was out of the beans at the beginning of the roast and concealed by it at the end. This one also moves the thermocouple off the rear wall and into the beans which was an improvement. This one, measuring BT throughout, I am guessing this gave them better (or at least more consistent) telemetry from which to save and then repeat roasts. Again, I have no knowledge of the specific programming or engineering reasons for the change.

I think the bottom line is this one may not be bean-temp accurate, but it is consistent batch to bath so can still be used to judge what is going on. I have played around with various thermocouple placements and designs, and being that the bean mass is so relatively shallow, even small movements or placements of the thermocouple give different readings.

Finally done!

As with Rama's, you can see where the beans are (clean part on the back plate) (225g load).


I've installed the BT probe at this height to ensure it cleared the pivot pin of the eject door in the back. I've followed Mark's (mutts) advice and lowered the ET height by about 1/4".



I used increasing sized drill bits, until 3/16", but I should have staid with the 11/64" bit and played with it to ensure a tighter fit. As I didn't have at hand products such as JB Weld (nor did I want to permanently fix the TC end), I've used some folded steel paper clip to wedge the TC wire in place. Simple but steady.

The BT probe is about an 1 1/4" long, so I could get well into the bean mass and avoid stem effect, but this makes it very important that the wire is kept bent, else it collides with the drum fin (which did happen the first time I tried the setup before putting everything together).

I've used an x-acto to cut a small part off the bottom of the back plastic panel, making a clean job.

I'm pleased with the result.

Again, thank you all for your info/feedback.

Someone in my Home roasting neophyte: a roasting log has asked for more pictures of my setup on the Hottop. I thought it would be best to keep things tidy, so here they are in the appropriate thread.

In the inside, nothing fancy, a few tie wraps to keeps the two wires together. From their tip, they go under the motor, turn down on the edge of the wall separating the upper (motor/fan) and lower (electronics) parts of the Hottop...


and the wires come out from the bottom of the back panel...


... in which I cut a small rectangular hole to accommodate the two wires. The Hottop feet seem high enough to prevent the wire from doing a sharp 90° bend. I think it should be fine.


To keep the end of the thermocouple wires in place in the roaster, I use folded paper clips, wedging the wire in its hole. If they get loose, they cannot fall off: they are too big to go through the hole toward the back part of the roaster, and the right angle ends keep them from falling in the roast chamber. Not a perfect solution but it seems to work well. This is a picture of one on a wire (just to show what they look like inside; I didn't take pictures before reassembly of the roaster).