I know the Ailllio Bullet has this, and I've been thinking about how to add it to my drum roaster without breaking the bank. I found one example here ( How do you know the temperature of the drum? ) that looks workable with a $70 Phidget. A more ubiquitous sensor is the MLX9614 which can be had for around $10 on Amazon, Ebay, etc. I originally ruled it out, because you have to keep the sensor under 125C, so didn't see how I was going to get it close enough to the drum and not have it overheat. In thinking about it and after seeing the above post, I think I could mount it in a non-contact way so it just looked through a hole in the drum wall. I'll put a pic below to show the scale. Not sure if I'd have to do something to create a little air flow in front of it to block escaping hot air. The MLX9614 even comes in some flavors (maybe less ubiquitous) that have narrower fields of view, so could be even further away. The above example aside, anybody tried this? I like the simplicity and cost of the idea.



As an aside, here's an interesting little description of the IR bean sensor in the Aillio:

https://aillio.medium.com/the-start-of- ... aa01d08fa9

I know the Ailllio Bullet has this...

I don't think this is what the Bullet does. I think the IR sensor in the Bullet measures the BT, not the DT. I can't think of a good reason to monitor DT, except for roasters with a heavy drum, and even then only as a means to ensure consistency at the moment of charging the roaster. In contrast, the drums in many home roasters, especially smaller ones (e.g., Quest, Huky, Kaldi) are relatively light. The minute the beans enter, the drum temperature quite rapidly cools, as it gives up what little heat it can store to the much cooler greens.

A couple of other notions spring to mind. First, as you allude to, some way of avoiding air being drawn into the roaster will be needed. Even leaving the trier out of its socket for a few minutes can drop the ET on small roasters. Perhaps a small piece of glass, like the V.1 Aillio, would work. Another consideration would be the reflectivity of the drum. You would have to calibrate the IR to account for that or paint the drum flat black.

I agree the bullet IR sensor is intended to measure bean temperature during roasting, although it does monitor drum temperature during preheat.

I'd also like to see drum temperature during roasting. It makes intuitive sense that charging the drum causes its temperature to drop, but how much? I assume that the popular 1 minute soak before turning up the gas is done to avoid overheating the drum. So the question is how fast can the heat be applied in the early phases of the roast? It is appealing to think of being able to adjust gas to maintain a constant drum temperature. Until now I've just been using trial and error, watching for obvious scorching or tipping. Does anybody have any drum temperature data early in the roast that shows what is really going on for our small roasters?

I've done a couple of temperature checks (handheld IR "gun") on the drum right before and after a 60 second soak. The drum is at 125C, then charge the beans in, wait 60 seconds, then check the temp again and found 100C. I had my BT probe in the beans before charge and it showed 24C, it was up to 51C at the end of 60 seconds. I'm a little blind when I'm using the IR gun, as the angle I have to shoot the drum temp prevents me from seeing what I'm shooting at... but it's a pretty big target and I know where it is. So not extremely precise, but I think a 25C cooling from the drum, while the beans rose 27C is in the ballpark. The similarity in the amount of rise and fall is just coincidence, I think. I was surprised when I calculated this out how much heat the drum is imparting into the beans, with no other heat source involved. The rise in the bean temp will vary depending on the temperature difference between the beans and the drum (bigger diff means higher rise). Obviously as the roast rolls on, the drum is going to heat up from that 100C low at end of soak. Once you put that heat into the drum you're kinda stuck with it eventually dumping it into the beans down the line. Sorta like hitting the throttle on your boat as you approach the pier - you can cut the engine, but you're going to keep going because of the momentum you put in earlier.

These observations were my motivation for wanting to start monitoring and planning for drum temp - I use the gas to store up heat into the drum that the drum then portions out into the beans. Well... except for the 5-10% or so of the heat that gets through the drum perforations... If I charge with too hot a drum, or put too heat into the drum too early, even though my BT might look ok at the moment, I'm forced into backing way off the gas down the road as BT goes high.

So after bothering to read the link that was so conveniently provided I see that @EddyQ did indeed post a very nice drum temperature curve. He mentions being surprised that drum temperature doesn't change much during soak, and if I'm reading his Artisan chart correctly it looks like a drop of only about 40F, which surprises me too. He mentions that in the end this information isn't too valuable, but it does seem like good data to acquire, once, for your particular roaster / profile / charge weight combination.

I could definitely see the importance of drum temp varying between roasters ( different total masses, materials, perforations, air circulations, venting, ratio of bean mass to drum mass, etc.).

I ordered the little IR sensor, and have no objection to drilling a 10mm hole in the side of my Kaldi Home, so will report back on if this is workable and, if so, some roasts with DT being recorded.

Cool. Someone else is interested in their drum temps. I think this approach is the easiest way to do it. And it is good to know what temps your drum is at. Especially if you have thoughts of modifying conduction to convection ratios.

A few things to keep in mind.
1) IR sensors can measure from a long distance away from the surface. The field of view, if narrow, can point and hit a patch on your drum from feet away. I think my Phidgets had 10degree field of view. This really helps to keep the sensor cool. And BTW, every IR sensor has a thermal sensor which measures its own temperature and does corrections. Best to keep them at a stable temp.
2) beware of possible IR reflections off drum. IR is light. I painted my drum with high temp flat black stove paint to minimize any reflected IR off walls and from burners.
3) I also have a thermocouple on the wall outside my drum in a location where any reflections might be "seen". There is a pretty simple math to correct temps if you know the wall temp and the emissivity of your painted drum. I think my IR is off almost 50deg without correction.

Once you get it up and working, you should test to make sure a burner setting of off to full blast doesn't change the temp with an instant change. If a sudden gas change creates a instant IR temp change, chances are you are partially reading or viewing reflections of burner. Think of this sensor as a camera looking at an object with the sun off to the side.

Good idea, I was thinking about exactly this a couple of weeks ago. I did find a sensor, but found it too expensive (IR402, similar copies are at Alibaba https://www.alibaba.com/product-detail/ ... ypass=true
The MLX9614 looks like a cheap alternative, worth a try. But it outputs from 3-5V.
The Phidget 1048 I am using (with thermocouples type K) doesn't work with this, does it?

Sensor showed up today. Only had time to fashion a little bracket for it out of 1/16" aluminum strip. Not sure yet if I'll try "hanging" ut from the top of the wall (as I held it in the photo), or flipping 180 and anchoring it at the bottom. I kinda favor having the bracket mounted on the bottom, holding the sensor up to the peep hole.

Dan Dyse wrote:Good idea, I was thinking about exactly this a couple of weeks ago. I did find a sensor, but found it too expensive (IR402, similar copies are at Alibaba https://www.alibaba.com/product-detail/ ... ypass=true
The MLX9614 looks like a cheap alternative, worth a try. But it outputs from 3-5V.
The Phidget 1048 I am using (with thermocouples type K) doesn't work with this, does it?

No, these things put out a digital signal, so wouldn't be compatible with a thermocouple. I recall Phidget's own IR sensor (which I thought may be a MLX9614 under the covers, based on the specs) plugs directly into USB, so doesn't plug into their hubs either. I've got an Aurduino which runs a servo hooked to my gas knob, so my plan was to wire this sensor into the Arduino, and let the Arduino put it expose it via modbus like it does the servo.