My second BT probe ...

[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...  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?

[edtbjon]

Yes, I was very surprised too, as you said that your probe was more responsive than the original one. To make sure that it's not a Phidget or Artisan issue, I disconnected the probe and connected it to a Center meter, which gave the same results.
Anyhow, I got a second (spare) 17mm probe which I'll try out tomorrow. (BTW, I'm in the impression of that the probes were manufactured to order, so maybe they are both faulty...)

About fitting the probe, I use an M6 nut.

Susan: I started out trying just to replace the original BT probe (in the original position). There's no need to post that graph too, as the results were the same, which I reported in the first post in this thread. Also, the idea is to replace the original BT probe, not to have an extra TC.

[beananimal]

Hello Björn,
now I am really confused about the results
and I am annoyed with myself - for not seeing it before  as I expextect anyway significant effects due to the 6mm thick double drum of my "fat Huky".

Then I have to give in, that I understand now that  I mixed up Phidget port 1 and port 4, so that all my interpretations were faulty.   

Then I gave the Huky to a friend for further testing and feedback, who then claimed that the behaviour is somehow strange and the thermal mass of the 5kg drum is too sluggish. Which seems now to have multiple reasons.

Now, the behaviour of my probes are similar with yours, being finally at ~170°C instead of ~210°C, while during calibration in hot water the 17mm probe was very fast and exact. Even installation on an aluminum profile did not change anything.

The idea that the frontplate is not as hot as the internal does not fit for me too, as I also have similar result within the exhaust, where there is excessive airflow and convection.

You did already double check the idea of having some errors caused by the phidget.

I'll install one 17mm from inside (improvization with teflon tape) to get it deeper into the beans and see if there is any change.

I still trust in the quality of these professional TCs and will call the sensorshop hotline the next days.

I am really sorry about that mess, especially as you drilled a hole in the frontplate - with a lot of effort.

peter

[edtbjon]

Don't worry about the extra hole. My Huky isn't a showpiece (even though it looks really good ), but a working tool.
Anyhow, I still want to solve this and have ordered a few cheap TC's from Ebay to play with. The idea/concept of a short TC seems perfectly good to me, as a shorter probe closer to the circumference should in theory give a more accurate reading, especially with smaller charges.
So, back to the workbench for some more experiments...

[beananimal]

I am one step further - in the darkness.

I had an open discussion / brainstorming with the hotline of the sensorshop (direct manufacturer of professional probes). 
They don't have any idea, but offered that I can send back the probes for checking. Best with some photos and description.

Today I did a roast with a TC for ET (original position) installed from inside, so that the hex-flange is inside the Huky. And outside some teflon-tape around the probe and a M8 nut to fix it. (to get it deeper into the Huky and avoid cooling by conduciton to the outside structure)
The temperatur shown increased much faster,  but as I don't have something direct to compare  I will do the same for the normal BT position.
(I dont want to use the double-wall-drum for comparability with other Hukys)

In the past a probe in the exhaust was my anchor point for everything, but
I just remembered that this was most of the time a cheap plain cable-probe I used already with my former Behmor. It was fast and plausible all the time. 

[hankua]

What's your take on how the changes affect the delta between BT and ET?

[beananimal]

Björn: I am now going for some 330g roasts with limited changes in TC setup.
(My older ones cannot be used because there were multiple changes in experiments on my 5kg-drum Huky with the new TCs)

The first roast July 16th was:
1) BTorigingal position: 70mm original Huky TC, shall remain constant as it gives traditional temperatures
2) EToriginal position: 17mm probe now installed from inside with teflon tape
3) Exhaust-elbow: 10mm probe normally installed from outside
4) BTadditional-40mmOffset:  17mm probe normally installed from outside

The next version will be changed to:
2) EToriginal position: 17mm probe normally installed from outside
3) Exhaust-elbow: plain cable probe fixed from outside
as today I killed a TC while trying to make a M6 thread on the outside part of the tip.
I'll post the photos and the Artisan graphs then.

[edtbjon]

Well, If'm thinking of where I can use my short TC's too. The first thing that I think of is the MET (outside there top of the drum. I'll check that tomorrow to see if it accords or deviates from my "normal" MET readings.
I'm looking forward to hearing about your experiments with replacing the ET probe with a 17mm one.

I'm also thinking about trying out bending a 70mm probe so that it sits better in the "middle" of the bean mass. Again, the videos are of great help, as it shows where to place the tip of the probe for best efficiency. Bending the probe is normal procedure with many other roasters, so why not giving it a try. After all it is (or: should be) the very tip of the TC which reads the temperature.

[beananimal]

With ET I meant the probe above the drum, so it is MET.

I used the last years a bent original Huky BT probe without problems.

[edtbjon]

With ET I meant the probe above the drum, so it is MET.

I used the last years a bent original Huky BT probe without problems.

ET ... MET, the most common misconception on this forum.

That's excellent with the bent BT. Now all I have to find is my brake pipe bending jig.

[edtbjon]

Well, I found my brake pipe bending pliers (jig). 3/16" brake pipes are much softer than the shielding for the TC probes... , but it's close enough to the 5mm shielding. (If you want to experiment, try to find something cheapish for bending brake pipes in your local automotive tools shop.) I.e. there was a few kinks on the bend, but nothing which broke the TC. The easiest way to bend the TC into the center of the bean mass was to bend it downwards. I simply bent the TC into a hook shape, got it fixed to the front plate and fastened the nut. Then it's easy to adjust the tip position so that it doesn't interfer with the agitation fins. (BTW, this probe position is the original hole, not from my extra 40mm off centre hole for a short probe.)
I also tried to use my "funny" 17mm probe in the MET position, but it was as sluggish there as in the BT position (as reported in the beginning of the thread). My "normal MET readings does shoot off through the roof (i.e. above 250C) between 4 and 5 minutes and is always well above the ET and BT readings, as compared to the very low readings in these graphs.
I do think that the "new" position of the BT probe tip is better than the original one. With my standard 400g charge there's more reaction than with the original position and with a 200g charge, there seems to be a very similar TC response. I will try charging e.g. 100g tomorrow to see if it produces reliable results. (With the original, 70mm straight into the roaster, position, roasting small charges gave unreliable and high readings. With 125g charges, which I documented a couple of years ago, the BT readings were more like a second ET...)
About the graphs below, the Guji is 400g and the Thimu is 200g.