Thermal camera for moist air - Page 1
Forum section: electronics / general

author: artag
author_rank: Super Contributor
timestamp: June 25, 2019, 10:22:07 pm
content: My experience of thermal cameras is limited to the rather low-spec Seek Thermal, but I'm considering whether I can use a thermal camera to monitor respiration.I want to get enough contrast in moving image to see the cloud of warm, moist air expelled as a person exhales.I don't need much detail - although some idea of volume would be useful, i don't care much about speed. I mainly just want to measure respiration rate from the period between cycles of exhalation.Yes, I know there are lots of much cheaper and more accurate ways of measuring respiration, but a thermal camera has some particular advantages I want to explore.Is this feasible at all, and if so, how 'good' a camera would be needed ?

author: Vipitis
author_rank: Frequent Contributor
timestamp: June 25, 2019, 11:08:45 pm
content: I am not sure this is even possible. You can see the temperature changing directly at the nostrils rather easy, even in LWIR. optical Gas Imaging uses cooled MWIR cameras with a narrow filter arround 3.3-3.5 micron. I don't have experience with those.Depending on the situation you want to use it in, you want to have a good setup with a matt background to see the gas. I remember seeing some images where exhalenwas visible in slow motion thermal, but I don't got it on hand right now. You will surely find some examples with Google.

author: Mr. Scram
author_rank: Super Contributor
timestamp: June 25, 2019, 11:13:04 pm
content: I think you'd be better off looking at Schlieren imaging, which is all about making air flow visible.

author: artag
author_rank: Super Contributor
timestamp: June 25, 2019, 11:59:28 pm
content: Nostril temperature would be fine if it keeps up with respiration, actually - I just assumed the moist air would be the biggest thing there.I'll try that with the Seek camera but would welcome reports from people with other cameras, especially relatively cheap ones like leptons.Thanks for the Schlieren link - that could well be worth considering too.

author: bap2703
author_rank: Regular Contributor
timestamp: June 26, 2019, 05:10:46 am
content: 'Moist air' aka water vapour is the main gas defining atmospheric transmission windows.Thermal cameras are designed not to see it!!!However if you could have water aerosol instead by doing your experiment outside during winter that could work.An option would be to inhale SF6 gas but that's not really advisable unless you really really really know what you do.

author: Chanc3
author_rank: Frequent Contributor
timestamp: June 26, 2019, 06:17:23 am
content: The moisture content in exhaled breath is definitely not high enough to be seen by a thermal camera - it is difficult enough viewing steam! Could always try getting someone to vape

author: Vipitis
author_rank: Frequent Contributor
timestamp: June 26, 2019, 07:51:34 am
content: This is what I found, but it uses a cooled MWIR camera that costs in the tens of thousands.http://graphics.ucdenver.edu/publications/Behavioral-Analysisof-Turbulent-Exhale-Flows-BHI-Exhale-2018.pdf

author: Ultrapurple
author_rank: Super Contributor
timestamp: June 26, 2019, 08:30:30 am
content: I like the way the report refers to developing "ahyper-sensitive FLIR thermal camera" (their emphasis).On a casual web search I couldn't find any more info about the device used beyond what's in the paper, a "FLIR A6788sc InSb CCF, 640x512 resolution" that "contains an embedded spectral filter that directly targets the CO2spectral band (3-5)" (sic) and operates at 30-120fps.Whatever the camera actually is, it's MWIR, probably cooled, carefully filtered and, as Vipitis says, almost certainly expensive. And, in this application, there's a lot of back-end processing going on to provide the information the researchers are looking for: in some ways that is actually more interesting than the camera itself, in that it shows a novel way in which a video stream may be processed to yield specific information.I agree with Mr. Scram that Schlieren imaging might be a good (and cheap) place to start. As far as I can see from watching a couple of YouTube videos andreading Wikipediayou can begin with an old telescope primary mirror, a flashlight and a razor blade.

author: Vipitis
author_rank: Frequent Contributor
timestamp: June 26, 2019, 09:00:10 am
content: I have wondered a few times if schlieren imaging can be done with a thermal camera. Your hit point source could be a soldering iron. It can be done with two colors using gels instead of a razor blade. I have only googled it once and don't remember funding anything spectacular yet.

author: Berni
author_rank: Super Contributor
timestamp: June 26, 2019, 09:26:59 am
content: Quote from: Vipitis on June 26, 2019, 09:00:10 amI don't see why it couldn't be done with a thermal camera.Tho the question is more why would you want to do it with a thermal camera. This sort of schilren photography is just a very sensitive way of seeing differences in refractive index. There is no special benefit in using long wavelength infrared for it, apart from perhaps looking at refractive index inside something that is not clear to visible light(Like smoke).

author: Fraser
author_rank: Super Contributor
timestamp: June 26, 2019, 10:50:51 am
content: The camera used is a ‘tuned’ version of the A6750 MWIR cooled camera. It has a 4.2 to 4.4um bandpass cold filter to image CO2 gas. This is the same technique as used in Industry to image various gas leaks and emissions. Specialist filtering is used to select the area of spectrum that best displays the gas of interest. The area where the has has the lowest transmission is often chosen as this highlights it against the ambient background. The industrial camera for CO2 detection is the GF343. Specs provided below.https://www.flir.co.uk/products/gf343/The A67xx is a descendant of the Indigo Merlin MWIR camera. And yes, it is an expensive unit. I am wondering whether my SC4000 could image CO2 if an appropriate filter were fitted in front of the lens. Such filtering is likely not optimal due to filter self radiation but the camera is likely sensitive enough for the task. The problem would be finding the required bandpass filter at reasonable cost.Imaging ‘invisible’ gases can be challenging but if thermography is to be used, it is far more effective than trying to image water vapour as has been stated. Sometimes a gas can be imaged by viewing its effect on the surroundings. If a person breathes CO2 out into an atmosphere that reacts with the CO2 to create a cloud, a normal visible light camera and suitable lighting could be used. The NIR spectrum is also easily and cheaply available for such experiments with CO2 and other gas reactions as well. There is the safety issue of not breathing in the ‘indicator’ gas though ! There may be safe indicator gases but I have no knowledge on the subject. I compare this to a sort of litmus paper reaction imaging but I am no expert in such. You need a chemist to help with CO2 reactive gases that create a visible ‘cloud’.In the tests using MWIR thermal cameras you are really just making use of the particular area of the spectrum that can show CO2 gas low transmission. You are viewing the CO2 gas getting in the way of the ambient background thermal emissions. This is a common technique for detecting invisible and otherwise non detectable ‘targets’. This is the sort of research being done to detect a Stealth Aircraft or Submarines ..... you cannot see the target but you may see the effect that it has on the surrounding environment.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: June 26, 2019, 11:03:27 am
content: A FLIR document on imaging gases.......https://www.flir.co.uk/globalassets/imported-assets/document/ogi_010_us.pdfHope this helpsFraser

author: Fraser
author_rank: Super Contributor
timestamp: June 26, 2019, 11:10:29 am
content: I just looked up the spectral signature for CO2 gas..... it is stated as being centred on 4.3um, hence the use by FLIR of a 4.2 - 4.4um filter in their CO2 detection camera.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: June 26, 2019, 11:14:46 am
content: FLIR demo videohttps://youtu.be/O1fJ3UuSFaUFraser

author: Fraser
author_rank: Super Contributor
timestamp: June 26, 2019, 11:18:00 am
content: A paper on the topic of gas detection is detailed here...https://www.ama-science.org/proceedings/details/380The document is free to download using the link below the abstract.Fraser

author: Ultrapurple
author_rank: Super Contributor
timestamp: June 26, 2019, 12:26:10 pm
content: Thanks FraserAs usual, a very thorough investigation and set of results (we expect no less from you!)

author: Fraser
author_rank: Super Contributor
timestamp: June 26, 2019, 12:38:43 pm
content: Total honesty from me..... a little bit of prior knowledge on the topic and the FLIR A67xx camera, combined with 10 minutes of googlingFraser

author: Max Planck
author_rank: Regular Contributor
timestamp: June 26, 2019, 06:01:16 pm
content: As mentioned earlier, it can be done easily by detecting exhaled CO2 using a camera like FLIR GF343. No need for any IR source. Just background radiation is enough. See picture of exhaled CO2 below.There are just two minor details. This camera, like many others for optical gas imaging, is using a cold filter integrated in the dewar, which cannot be changed, and the price tag.If we are talking warm filter (lens mounted or filter wheel mounted) one has to take into account the influence of the filter itself (radiation and reflections).The question is, what exactly you want to achieve and in what conditions.Max

author: Ultrapurple
author_rank: Super Contributor
timestamp: June 27, 2019, 12:54:44 pm
content: Just for fun‡I asked my partner to breathe out heavily while I pointed a sensitive uncooled LWIR camera at her. There was absolutely no trace of exhalation that I could see. We were in living-room conditions but there'd be at least a 10°C difference between exhaled air and ambient.I suspect it might work if we were in a cold environment, with the moisture in the breath condensing, but that's easily enough visible with the naked eye.‡ We have strange ideas about what constitutes "fun".

author: Vipitis
author_rank: Frequent Contributor
timestamp: June 27, 2019, 01:11:09 pm
content: For the demo video above, FLIR set up two cameras. One filtered and one not. However they only showed the filtered version. Surprisingly they answered my comment and just claimed the unfiltered MWIR band wouldn't have anything visible.The image attached is one I created as a center dual page image for a zine I created(it's done but I need to find a good printing service for it). This is done with the Lepton in my phone and you can definitely see the inhale and exhale. But leptons are 8.7hz so it doesn't look that great. On my new cameras it looks far better.

author: bugi
author_rank: Regular Contributor
timestamp: June 27, 2019, 02:54:09 pm
content: Quote from: artag on June 25, 2019, 11:59:28 pmLooking at my own open mouth and nostrils was like 3rd thing I tried with my TE-Q1, out of curiosity. I was actually just trying to see how my face looks in thermal, but during that I noticed the effect in nostrils and studied it a bit more. Breathing shows up very clearly, at least for normal (or heavier) breathing. Especially the temperature change during inhale was easy to notice. One does need quite a good view into nose, though, i.e. limits the angles.

author: artag
author_rank: Super Contributor
timestamp: June 27, 2019, 09:39:01 pm
content: 'The question is, what exactly you want to achieve and in what conditions.'I want to measure respiration rate with a non-contact sensor under typical room conditions and without asking anything special of the subject.Oh, and for a few $100 (I didn't say that before but you correctly guessed that a dewar sensor probably isn't a suitable solution)Some very interesting answers, thank you all for the input. I hadn't realised that it was so difficult - I thought the warm water vapour would be fairly easily visible, but the nostril temperature is definitely a useful possiblity. Schlieren photography looks interesting but the optical path would be difficult to arrange for the situation I have in mind (for one aspect I want to measure the respiration of several members of a group simultaneously).

author: Fraser
author_rank: Super Contributor
timestamp: June 27, 2019, 10:53:35 pm
content: There is a very easy way to carry out non contact measurement of respiration rate, just use one of the commonly available, very sensitive CO2 sensors and use some simple software to log the output and process the CO2 peaks into breaths per minute. This CO2 sensor technology is very sensitive to the output of a human and is even used to detect buried survivors in collapsed buildings. I have seen the output of these sensors clearly showing respiration rate when more than 0.5m from the person. You see peaks and troughs of CO2 as the breath reaches the sensor. This solution is non contact, relatively inexpensive and definitely a DIY prospect using something as affordable as an Arduino plus the CO2 sensor.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: June 27, 2019, 11:01:16 pm
content: A link to the sort of CO2 sensors I saw monitoring respirationhttps://www.sstsensing.com/product/sprintir-6s-fast-response-co2-sensor/Fraser

author: Fraser
author_rank: Super Contributor
timestamp: June 27, 2019, 11:27:43 pm
content: A complete development kit is available at reasonable cost. You just need to add some silicone tubing and a small constant air velocity air sampling pump (not a fish tank pump as that pulses too much skewing the readings). You could try using it in direct sampling mode without the flow through adapter but that is likely to require closer placement to the person as the sample is collected passively and the sample chamber is not actively flushed between breaths. Some experimentation would be needed but the development kit gets you most of the way without having to build anything or write sampling softwarehttps://uk.rs-online.com/web/p/sensor-development-kits/1809033/Fraser

author: eKretz
author_rank: Frequent Contributor
timestamp: June 30, 2019, 01:37:41 am
content: The nostrils do show respiration pretty vividly. Here's a short video I took of my little boy while he was sleeping. Inhalation and exhalation are very clearly distinguishable.https://youtu.be/NrufyuN8JcU