Cheap thermal imaging? - Page 1
Forum section: electronics / general

author: casterle
author_rank: Regular Contributor
timestamp: December 22, 2020, 04:03:01 am
content: A few months ago I was looking for a cheap video camera to keep an eye on my 3D printer. I noticed that they came with and without IR filters. A couple months ago I'd seen thermal cameras used often enough on various YouTube videos that I wanted one. But the cost is outrageous!Why can't I get one of those $20 cameras (which work great, BTW) sans the IR filter, add appropriate filtering to get rid of visible light, and have an IR camera for relative peanuts? I assume I can't because if I could they'd be a lot cheaper, right? Why are these things so damn expensive?

author: DaJMasta
author_rank: Super Contributor
timestamp: December 22, 2020, 05:08:48 am
content: The infrared band is very big, large enough that NIR security cameras with "night vision" and LWIR thermal cameras are in very different bands of the EM spectrum - cameras that are sensitive to infrared in the normal thermal band (a wavelength of about 7.5um to 14um) have filters to keep out other bands so that they can get an image of thermal IR exclusively, whereas NIR security cameras and the like (visible band to 1100nm or so, depending) are standard visible light sensors that have filters keeping IR out removed (if left in, they can cause image issues with strictly visible imaging in some cases) or with enhanced sensitivity in the NIR. The spectrum between the end of NIR and LWIR is taken up by other cameras - SWIR to 2.5um or so and then MWIR from 5um or so (with big drop-outs in the spectrum thanks to high atmospheric absorption that make chunks of the spectrum basically opaque in regular air) - and these detectors are typically made of different materials than the VIS/NIR standard detectors and the LWIR thermal detectors. The in between bands can give you thermal information, but they only have meaningful thermal data for things at higher temperatures - a very hot item will give off radiation in the SWIR band where a room temperature item won't give off anything in that short a wavelength, and while room temperature objects give off MWIR band radiation, the detector's own heat generation will blind itself unless it's chilled, typically cryogenically, to give off little enough to be able to image from other sources.So the short of it: different sensors for imaging in different bands and filters to make sure out of band radiation doesn't obfuscate meaningful data.

author: bap2703
author_rank: Regular Contributor
timestamp: December 22, 2020, 01:12:54 pm
content: Just a precision:- NIR infrared camera, like security camera, are active devices that rely on a light source to illuminate the scene (in the near infrared).- Night vision devices might even use very faint source like the glow from the sky but that's more military stuff, certainly not a $20 device- What is called "thermal cameras" are passive devices that rely on the emission from the objects themselvesIf it's cheap it's silicon and NIR

author: AkiTaiyo
author_rank: Contributor
timestamp: December 22, 2020, 02:04:24 pm
content: If you are willing to build something, then you can use fairly cheap thermal imaging module like these. They talk I2C and you can use a simple microcontroller or Raspberry Pi to provide an interface. Using a single RPi would allow you to get both a visual and thermal stream depending on how complicated you wanted to get.https://www.mouser.co.uk/Search/Refine?Ntk=P_MarCom&Ntt=145139989They are low resolution so the image you get out of them wont be amazing at all, nor will the temperature be accurate if that what you need (but the latter also applies for a lot of thermal imaging situations).Attached in an example of my 3D printer in thermal using a simple 80x64 IR module, which is quite a bit higher resolution than the one linked above, and it still looks terrible.On a side note.. You can usually start seeing emissive radiation on NIR cameras once the target is greater than about 500C (emissivity dependent!)

author: casterle
author_rank: Regular Contributor
timestamp: December 22, 2020, 11:31:30 pm
content: Quote from: AkiTaiyo on December 22, 2020, 02:04:24 pmThanks for the link - now I at least know the class of sensor involved. Iwaswilling to build something, but I saw the price and resolution of the sensor...which clarified for me that this was a want rather than a need, and I don't want itthatmuch!

author: casterle
author_rank: Regular Contributor
timestamp: December 22, 2020, 11:36:46 pm
content: Thanks to all for the information. It seems that I won't find what I want for a price I'm willing to pay.But I wonder, how does this work with phones? I see people use them for thermal imaging, even with temp readouts- do they have one of these expensive sensors just for that purpose?

author: Vipitis
author_rank: Frequent Contributor
timestamp: December 23, 2020, 01:08:33 am
content: you can buy phone dongles. there used to be only FLIR One and Seek, but nowadays you get a whole range of options and quality from thermopile to chinese to ThermExpert and ThermApp.The best option for you probably is to grab a used FLIR One or salvage a Lepton 2.5 with shutter and radiometric. put that on one of the boards and pipe it into your printing computer. you can fined used FLIR ONE (old gen) for cheap on ebay. not 20$ cheap thoif you want to monitor your build surface, what kind of surface are you using. Because emissivity could be an issue if it's a metal print bed. PEI or any of the fancy coated stuff might not be a problem tho.

author: casterle
author_rank: Regular Contributor
timestamp: December 23, 2020, 02:33:58 am
content: Quote from: Vipitis on December 23, 2020, 01:08:33 amThanks. Now I know what to keep an eye out for.I've got a regular camera for my printer; I wanted an IR camera to look for hot parts on boards, etc.

author: DaJMasta
author_rank: Super Contributor
timestamp: December 23, 2020, 05:03:37 am
content: If you look for older model cameras from lesser known companies (i.e. not FLIR), or look for thermal camera cores, a decent unit can be had for $100-200 - a far cry from $20, but inexpensive compared to many. If you're looking for board inspection work, though, you want to make sure the minimum focus distance is reasonable, or that the field of view is narrow (longer standoff distance, but still close in resolution on a small target) - most of the inexpensive cameras do not come with optics that are easy to focus, so the fixed focus setting has to be one that suits your use case.There are some cores like those used in the Seek thermal devices that are relatively high resolution for the price (especially compared to a lepton core or similar), but the image quality is often somewhat lower than equivalent resolution better sensors. You also run into a lot of cheaper cameras and cores that are not radiometric or only have a center spot measurement, meaning while you can get a great looking thermal image, the camera isn't calibrated to read out temperature on any pixel, so while it's good for inspection, it's not really suitable for measurement.Especially older Flir One modules, since they require older phones to attach to, can be found fairly inexpensively for the quality of the core in them, it just may require that you buy an old iPhone or similar to use it.

author: casterle
author_rank: Regular Contributor
timestamp: December 23, 2020, 08:18:47 pm
content: Quote from: DaJMasta on December 23, 2020, 05:03:37 amThank you for your detailed explanations. I've got an old LG E980 lying around unused; it was a pretty high-end unit in its day - large hi-res screen and camera. Do you think an old Flir One would work with it? Were there different Flir One models for different phones, or would any Flir One do?If so, I've got a good option, and I'm not in a hurry so I can wait for one to show up.

author: casterle
author_rank: Regular Contributor
timestamp: December 24, 2020, 10:38:26 pm
content: Quote from: barycentric on December 24, 2020, 08:51:26 amIf I want to look for hot components, is resoluton < 60x60 useful?

author: Dennis Frie
author_rank: Contributor
timestamp: January 01, 2021, 04:49:01 pm
content: Should be good enough to search for hot-spots on a PCB.A few of the handheld thermal imaging devices uses 60x60 pixels, which can be a great tool even with the low resolution. With that said, it's a lot more fun to work with the high resolution camerasIt should be added, the ability to focus up close, makes a significant difference when looking at small components on a lower resolution (like checking for excessive power dissipation in 0402 components etc).

author: DaJMasta
author_rank: Super Contributor
timestamp: January 01, 2021, 06:01:22 pm
content: Yes, 60x60 can be useful, but as indicated in the last post it depends on a lot of things. One important one for board inspection is minimum focus distance - a good camera is often 10-15cm, but many can be more than half a meter, and the farther away you are, the more pixels you need to see the same size part on a board clearly. The other part of that same issue is the field of view of the optics - a narrower field of view lets you see less up close, but concentrates that lower resolution on the smaller target, so you effectively get pixels corresponding to smaller sizes - it also helps offset high minimum focus distances.If it were me, I'd aim for 80x60 or so as a bare minimum, look for something with a lower minimum focus distance, and then get something with MSX or similar image overlay/combination processing to get more detail. A low resolution sensor with a visible overlay can give you quite a bit more detail on the target to show you exactly what part you're looking at, and for something like spotting hot components, that's plenty. Knowing that a spot is hot and which part on the board it corresponds to is usually sufficient, rather than comparing temperatures of adjacent passives or similar.

author: Bill W
author_rank: Super Contributor
timestamp: January 02, 2021, 01:08:56 pm
content: MSX is particularly hopeless clsoe up as parallax is a bigger and bigger problem. It would need setting up each time, unless you made a fixed inspection bench.A brief power up and then find the hot spot by using a cold screwdriver works better.Bill