Hey guys , I just started roasting 900g batches for the past few days… this has been happening. On smaller batches I haven’t had this issue. But as you can see IBTS merges with BT right after 1st crack. Is this an issue with IBTS sensor ? Maybe needs to be cleaned ? Or this is pretty normal.
Thank you for your feedback …
Hey dkrylov, not gonna say one way or the other if this is good or not. It happens to me also when I am roasting large batches. I believe it has everything to do with the thermal mass being large enough at those size batches, when the beans start to go exothermal, the mass available just keeps getting hotter and hotter and with increased air flow, the drum cools faster than what the beans will. I am usually so close to dropping when that occurs I haven’t worried much about it, and still have awesome results.
This has begun happening to me and recurs after only 5 or 6 454 gram roasts. I have to clean the IBTS with a dab of alcohol to remedy it…after every 5 or 6 roasts; quite a pain. If I do not do this, the curves will intersect 7 minutes into the roasts with the probe then indicating a temperature higher than the IBTS. I thought I read somewhere some time ago that it was an imperfect seal with the fan seating that caused this. I have taken the thing apart and attempting to re-seat the fan three times but I have been unable to get it secure. The rubber mount seems to be too flimsy …or more likely I’m just an idiot. That being the case, there are more than a few of us it seems, judging by other users roast curves
@Larz If your sensor gets dirty so easily, then its not installed properly / not sitting properly in the silicone.
You can read the guide here to seat it properly (page 5)
Jonas
I would check if the IBTS is clean.
If there are problems with the IBTS sensor getting dirty then you can try to seal the plastic part to the silicone part with a little bit of RTV silicone around the edge. It should not be necessary but can help.
On a large batch size, over time, the bean probe reading will become more and more accurate and therefore closer and closer to the IBTS temp. If you think about this it makes sense, as a drum full of beans will result in much more heat being transferred to the probe. This is why, for instance, with a low batch size of 350g, the bean probe will never really catch up to the IBTS and your first crack temperatures will appear far lower. Whether the tendency for the bean probe temp to exceed the IBTS by a few degrees on large batches over time is an indication that the emissivity of the IBTS could be adjusted further is still unclear. Our early experiments indicate the emissivity setting is on point, but we plan to take the tests a step further once we can design a rig to dial everything in with more precision. For now, however, we’re quite happy with how consistent the IBTS is as a reference point across different batch sizes – that’s what matters most and what makes it far superior to the old probe.
Thank you Jonas. Yes, as I mentioned in my post, I’ve attempted to re-seat it properly 3 times… the problem is no doubt with the idiot at the end of the screw driver here. Next attempt I’ll begin before I have a couple of scotch, not after.
Makes a lot of sense, I checked my sensor and there is nothing wrong with it. Everything seems to be clean , and no issues.
LOL, who knows, that might help!
As Jacob said, you can also try with to seal it up with a small amount of silicone.
If you are using roastime, please confirm how fast the IR Fan is running -
Jonas, the IR fan is running at 15840 RPM.,…sounds smokin’ fast.
That sounds about right.
Have you updated to the latest firmware and calibrated your exhaust fan?
You can go to menu item 6 and press the top left button - then wait for it to calibrate. I would really like to find out what is causing this issue.
Next time you have it off, please take some pics and share them so that I can see if something is wrong or not.
Jonas
Yes I previously calibrated my exhaust fan Jonas. I have a tight schedule for a couple days but will be reinstalling the IBTS shortly and will send some pics and let you know if I discovered obvious user error with the previous installation(s). Thanks
I can confirm the curve differences between a load of 500-600 gr vs. 900 gr. When the batches are relatively small, the IBTS and BT run almost parallel during the full roasting process. However, when I roast 900 gr, the curves merge and even cross a liter around 200 C. At the. e end of the roast I rend to focus on the IBTS curve. For the larger volumes this means that I focus on the lower temp indicating IBTS. I wondered whether there is something wrong, but now I think that indeed the BT is more accurate with larger bean volumes compares to smaller ones. The IBTS is more stable. My machine has the IBTS and the new power board, both installed afterwards. For 500-600 gr batches I use a preheating temp of 230C and for 900 gr 285C.
Jonas , further to all this, I reinstalled the IBTS in an effort to determine if that as an issue. As I mentioned, previously it did not feel securing mounted (“wiggly” being the term I used), after reinstalling it 3 times. Once again after dismantling the thing, it had become looser than desirable , with light visible around the base. HOWEVER, I discovered that by using a center punch and large hammer I was able to force the two pins further into the silicone/rubber base , thereby creating a tighter, more secure mount, eliminating any light around the edges. (OK, so i didn’t really use a hammer 
but the center punch gave me the careful leverage I needed to force the pins all the way into their intended receptacles. ). I have done a few roasts and will report back as to whether this was the source of the problem… I am almost certain it was. I guess I exercised an overabundance of caution previously when connecting the pins. Perhaps that is responsible for the problems others have had with this also.
I think we are discussing two different situations: one is the merging of curves with 500 gr of load as reported by Larz, which sounds abnormal. The other one occurs with loads around 900 gr and late in the roasting process and has been reported by several people. Question is if this one is a normal phenomenon? Or should we also check our sensors?
See my post above. As long as it’s a few degrees it isn’t a cause for concern. We may adjust the emissivity for IBTS in the future, but only if our experiments indicate that we should.
@kafei, can you please be more specific?
Sorry to be so pedantic, but it’s kind of important for us to understand this.
Interesting. I consistently roast 900g batches and almost never have the BT exceeding the IBTS. I’ve had issues with my IBTS getting dirty after only a few roasts and as Jacob suggested, have applied the RTV silicone to completely seal it up.
Celtic:
Referring to my only post above: “On a large batch size, over time, the bean probe reading will become more and more accurate and therefore closer and closer to the IBTS temp. If you think about this it makes sense, as a drum full of beans will result in much more heat being transferred to the probe. This is why, for instance, with a low batch size of 350g, the bean probe will never really catch up to the IBTS and your first crack temperatures will appear far lower. Whether the tendency for the bean probe temp to exceed the IBTS by a few degrees on large batches over time is an indication that the emissivity of the IBTS could be adjusted further is still unclear. Our early experiments indicate the emissivity setting is on point, but we plan to take the tests a step further once we can design a rig to dial everything in with more precision. For now, however, we’re quite happy with how consistent the IBTS is as a reference point across different batch sizes – that’s what matters most and what makes it far superior to the old probe.”
Referring to the end of the temperature difference between the bean probe and IBTS. I’m saying it isn’t unusual to see that particularly with larger batch sizes over more time, which makes sense for the reasons outlined above.
A few is just that… a few degrees. C or F. If you’re asking whether there is a specific threshold over which it becomes abnormal, there isn’t an official one, but if you’re starting to see the bean probe exceed the IBTS by a significant amount, then that would be something we’ve never seen before and indicate something unusual.
Just roasted 1000g for the first time and after 15 minutes, the bean temp read 242c and the IBTS read 235c. Things got hot - and normally, I dont roast to these levels but, I too noticed the sensors merging. Just cleaned the machine, too.
