Strange visible heat - Hikmicro B20 & M30 - Page 1
Forum section: electronics / general

author: katzenhai2
author_rank: Regular Contributor
timestamp: December 13, 2022, 04:35:57 pm
content: Hello,I took pictures with two different thermal cameras and now I'm wondering about the differences. Photos were taken with a switched on carbon filament lamp (20 W). I can see the carbon filament with the Hikmicro B20 but not with the Hikmicro M30.Here are a few technical details of the cameras:Hikmicro B20Pixel pitch:12 µmResolution: 256 x 192NetD: <=40mkLens: F1.0FOV: 37.2° × 50.0°Spectral range:7.5 to 14 μmFocal length: 3.6IFOV: 3.3 mradFixed FocusHikmicro M30Pixel pitch:17 µmResolution: 384 x 288NetD: <=35mkLens: F1.0FOV: 37.5° × 28.5°Spectral range:7.5 to 14 μmFocal length: 9.7IFOV: 1.75 mradManual FocusOf course the focus of the M30 was set correctly and the temperature range (100°C - 550°C) was also adjusted.What could be the reason for this? At the moment the only thing that comes to mind is the spectral range. Maybe the marketing department just copied values ​​into a table without being exact? Or what other reasons could this have?Attachments:1. B20 (Temp.Span 50 - 80°C)2. M30 (Temp.Span 50 - 80°C)3. M30 (Temp.Span 70 - 100°C)4. Visible Photo5. B20 (Temp.Span 70 - 100°C)

author: katzenhai2
author_rank: Regular Contributor
timestamp: December 15, 2022, 07:16:01 pm
content: Nobody with an idea why I can see the carbon filament (through the glass) with the B20 but only the (outside) glass with the M30?

author: Vipitis
author_rank: Frequent Contributor
timestamp: December 15, 2022, 07:37:44 pm
content: different coatings, different lenses, different sensor. Glass is usually reflective and not transmissive. It seems even emissive in one of the images. So it's not ordinary glass

author: Dark Volter
author_rank: Contributor
timestamp: December 15, 2022, 09:29:47 pm
content: I figured it out !This was interesting to think about, and why you were seeing that.I've heard mid wave cameras can see thru special glass, but these arent mwirAnd spectral response dictates alll, unless something really novel and unknown is happening lolSo, I started looking up the cameras even with your excellent detail here, and then figured it out seconds before I saw itLook herehttps://monroeinfrared.com/product/hikmicro-m30/https://www.hikmicrotech.com/en_us/industrial-products/b-series-handheld-thermal-imager.htmlBoth cameras also have a visual camera, and also a fusion modeTherefore, the m30 here happens to be in fusion modeLOLThis would have been something. .. really notable and worth looking into otherwise,I mean, a possible sapphire glass bulb and Mwir handheld uncooled camera? Today???It could Happen at some point in the future....In hindsight, image 1, the top looks far brighter than the rest of the filament. I Don't think a thermal camera seeing that would have that glow around around the filament, a hot filament would look.a bit uniform, but definitely less blowout-y on a Thermal camera . In visible though, the brightest part will cause a glow like that often,

author: ArsenioDev
author_rank: Frequent Contributor
timestamp: December 15, 2022, 09:44:47 pm
content: Speaking of Sapphire Glass and cameras, I have two large sapphire domes I need to do something with.May see if my FLIR contacts will loan me a MWIR camera for a bit to goof with

author: katzenhai2
author_rank: Regular Contributor
timestamp: December 16, 2022, 12:26:44 am
content: Quote from: Dark Volter on December 15, 2022, 09:29:47 pmNo. You are wrong.The visual camera isn't working in this mode (only thermal mode) and the camera which saw the filament is the B20, not the M30 (although both have a visual camera).Seems you need to figure it out more.But thanks.Quote from: ArsenioDev on December 15, 2022, 09:44:47 pmThat is interesting. Does this mean that my tests here are unusual for the thermal experts on the forum?I might have thought that something like this wouldn't be unusual if the spectral range were a bit different. After all, two different sensors (12 and 17 µm) are installed here....and I was wondering why nobody replied to my post.I'll do better thermograms of the lamp. I know I can get a better image of the carbon filament because I've done it before and didn't think much of it at the time because I've only had the m30 for a few weeks and couldn't compare.Though I don't know of this glass type this bulb is build. Its from the 60-70's.

author: katzenhai2
author_rank: Regular Contributor
timestamp: December 16, 2022, 12:58:29 am
content: I made better thermograms with the HIKMICRO B20 (see attachment) of the carbon filament lamp.The thermal camera is set up in such a way that it simultaneously saves a thermogram and a visual image at the same time so that you can remember later what you have thermographed.1. Picture: Thermogram of carbon filament (thermal mode)2. Picture: Optical pic of the cabon filament with the optical lens of the thermal camera(both photos were automatically taken at the same time)3. Picture: Thermogram of carbon filament (thermal mode)4. Picture: Holding the optical lens of the thermal camera closed with a finger: black optical image5. Picture: Thermogram of carbon filament (Fusion mode)6. Picture: Thermogram of carbon lamp with HIKMICRO M30 (thermal mode) - I am reflected in the glass pane of the lamp which is not the case with the B20Incidentally with the B20 it even looks as if you can see the reflection of the filaments inside the glass bulb. Or am I crazy?See next post with a better optical image.

author: katzenhai2
author_rank: Regular Contributor
timestamp: December 16, 2022, 01:05:54 am
content: Btw this is a better visual representation of the carbon filament bulb (taken with aCanon 7D).The carbon filament bulb were manufactured between 1960/1970.

author: Dark Volter
author_rank: Contributor
timestamp: December 16, 2022, 03:26:58 am
content: I see, that fusion Pic does appear different . Yeah, if covering the cameras separately doesn't work , then thats not itThe next conclusion then, is indeed the material making the 'glass' is something unique ...And since both cameras aren't setting thru, would also mean that the 7.5 - 14 isn't an exact equal between both cameras,and that some band is getting thru that one camera happens to see. It'd take a...thermal spectragraph of sorts to find out what wavelengths are getting through.It might take infrared windows, and bandpass filters - trying different ones, to narrow it down. You should also bug anyone else you know with a thermal camera to take a peek! If you were in the US I'd bug you and bring out my cameras lolI will say, I don't expect the pixel pitch of the cameras, the 12 vs 17 um, to make a difference on its own. Unless the pixel size ends up affecting the listed ' 7.5 to 14' response- but that would be news, and even then, the main question is the wavelength getting through the bulb.This is a bonafide mystery. ...I'm really curious now.Hah, I'd also be sending emails to hikmicro, flir, and seek asking them about this mystery

author: Dark Volter
author_rank: Contributor
timestamp: December 16, 2022, 03:37:15 am
content: There's a very few similar cases of this that popped up in my searches, and I found thishttps://www.eevblog.com/forum/thermal-imaging/seek-thermal-imagers-can-see-swir/So, there's def more to this phenomena. ...

author: cejoba
author_rank: Regular Contributor
timestamp: December 16, 2022, 11:42:12 am
content: This is very interesting indeed.My theory here:As a micro-bolometer, they have the same sensitivity across all spectrum. But usually only LWIR is strong enough to be detected by uncooled sensors. Other bands are also filtered by camera design typically.According to Planck's law, your hot filament may emit enough MWIR/SWIR energy to be detected even by uncooled sensor, and, combine with a camera design that is not active blocking those frequencies, you may get luck to see it.

author: Bill W
author_rank: Super Contributor
timestamp: December 16, 2022, 12:18:48 pm
content: Some sensor designs use resonant cavities under the pixel to boost responsivity, so a cavity set for 10um will also have a peak at 5um

author: Fraser
author_rank: Super Contributor
timestamp: December 16, 2022, 12:19:46 pm
content: It may be helpful to consider what we are actually seeing here..1. A carbon filament thermal emitter operating at high temperature producing significant thermal energy2. A fine glass envelope surrounding the carbon filament of unknown glass type, thickness and IR transmission capability.A little test for the two thermal cameras as a hint to what is happening here ….. Place a standard photographic glass Skylight filter in front of your thermal cameras and view a gas hob flame. Question: what do you see ? answer: you see the gas hob flame but the temperature measurement is very low and effectively meaningless. How can the LWIR thermal cameras see the gas flame through photographic glass that is known to be incompatible with LWIR wavelengths where transmission is concerned ? The answer can be quite complex but boils down to a combination of microbolometer window filter specification, lens AR coating specification, photographic filter glass type, photographic filter Coating type, Photographic filter thickness and the source of thermal emissions in terms of delivered energy levels to the photographic filter and thermal camera. The photographic filter may not be a suitable material for the transmission of LWIR, but it only acts as an attenuator, some energy in the LWIR band will get through it and the magnitude of the thermal energy entering it will effect the magnitude of what is seen by the thermal camera on the opposite side. Now for the thermal cameras side of things….. a microbolometer is a broad spectrum energy detection device. In the case of LWIR cameras the microbolometer is fitted with a filter that restricts its view of the world to a range of wavelengths compatible with LWIR imaging. An optical filter is not perfect and they most definitely pass wavelengths outside of their specified range. How much leakage outside of intended range is dependant upon quality and quality dictates cost. Some microbolometers may be very well filtered for only seeing LWIR where as others may have a lower grade of filtering that passes some wavelengths beyond the stated band coverage. This is unlikely to matter in normal general use of the microbolometer. In front of the microbolometer there is a lens block that contains lens elements that are relatively broad spectrum in their transmission characteristics but a specific LWIR lens coating is normally applied to improve lens performance. Broad spectrum MWIR/LWIR AR coatings are used in specialist roles but would not be expected to be seen on a general use thermal camera system. The AR coating will act as a VERY broad spectrum LWIR transmissive filter but that is not its intended purpose so do not expect tight skirts ! Energy outside of the LWIR band will definitely pass through the lens.All of this boils down to the out of band transmission capabilities of the thermal camera optical path and the amount of out of band energy stimulating that optical path.The path in your case is as follows….1.Thermal energy is generated by a carbon filament operating at several thousand Kelvin2. Broad spectrum thermal energy hits the lamps glass envelope3. Many wavelengths of the source energy pass through the glass envelope whilst some are significantly attenuated due to the characteristics and thickness of the glass4. Broad spectrum energy from the carbon filament lamp enter the thermal cameras optical system. Some parts of the spectrum pass through easily (LWIR) whilst others suffer severe attenuation (out of band for the AR coatings)5. The energy that made it through the lens block strikes the microbolometer window that has a integral LWIR filter. Some wavelengths pass through the filter with ease and others are severely attenuated.6. The microbolometer is illuminated with the energy that passed through the window and filter.The optical path filtration is not perfect and relies upon attenuation of out of band wavelengths but the performance of the filtration is dependant on the quality of the filters used. If poor quality filtering is employed, the microbolometer will see energy beyond the intended LWIR range.Does it truly matter if a microbolometer LWIR filter is not perfect ? In general use, no it is not a big issue. Can an unfiltered microbolometer be used as a MWIR camera ? Not really, it is too insensitive so would only see very high energy sources well.A test for the OP…. Place your hand behind the carbon filament lamp with the lamp switched off …. Now look at the lamp with your two cameras. Can you see your hand through the lamps glass envelope ? No ? Well that is because your hand is a relatively low emitter of thermal energy and cannot overcome the path losses of the glass and thermal camera filtration transmission characteristics. Place a hot soldering iron behind the lamp and set it to a nice high temperature…. Say 480C and repeat the test. Can you see any sign of that soldering iron through the lamp glass ? You may but we are now passing the energy through two layers of the lamp glass so that may effect matters.A carbon lamp filament that is glowing is a source of significant thermal energy likely operating at a few Thousand Kelvin. I believe you are only seeing this unusual effect because of the energy involved that is overcoming one of your cameras less than perfect optical filtration. Why does one camera see the filament and the other not ? Only the manufacturer can explain that with their LWIR filter characteristics.It’s a theory anywayI did a test with a photographic filter some time ago. I will see if I can find it and provide the link here.Update… here you go, my test of a photographic filter as a measurement range extender…….https://www.eevblog.com/forum/thermal-imaging/range-extender-for-thermal-cameras-cheap-option-from-fraser/Fraser

author: wraper
author_rank: Unknown
timestamp: December 16, 2022, 12:40:25 pm
content: B20 has ZnSe lens which is transmissive in visible light spectrum, M30 has germanium lens which does not pass visible light.

author: katzenhai2
author_rank: Regular Contributor
timestamp: December 16, 2022, 04:52:34 pm
content: Quote from: wraper on December 16, 2022, 12:40:25 pmHow do you know what lens the B20 has? Isn't it more likely that it has a (cheaper) chalcogenide lens? Why ZnSe?@Fraser:Thank you for your detailed explanation. Sounds very plausible.The carbon filament lamp also radiates enormously in the infrared spectrum - especially since I have also dimmed it.I have some UV filter for an optical camera and will try some tests!

author: Bill W
author_rank: Super Contributor
timestamp: December 17, 2022, 10:55:45 am
content: Quote from: katzenhai2 on December 16, 2022, 04:52:34 pmZnSe is bright orange and transparent.With Ge or Chalcogenides you'll just AR coating (and similar on either)

author: Bill W
author_rank: Super Contributor
timestamp: December 17, 2022, 10:59:39 am
content: Quote from: Bill W on February 23, 2021, 01:04:10 pmUpdate post - found the back referenceBill

author: katzenhai2
author_rank: Regular Contributor
timestamp: December 17, 2022, 04:54:01 pm
content: Quote from: Bill W on December 17, 2022, 10:55:45 amThe B20 lens isn't bright orange and transparent, that's why I questioned it. But obviously coated with something. I thought ZnSe lenses could also get a coating. Then of course it wouldn't be optically identifiable what they were made of.@Bill W:Too bad it worked with a germanium lens because otherwise could have been "proof of quality" for the type of lens used.

author: wraper
author_rank: Unknown
timestamp: December 17, 2022, 09:37:46 pm
content: Quote from: katzenhai2 on December 16, 2022, 04:52:34 pmI've seen someone mentioning ZnSe when googling. Then after this post I googled again and think I'd actually read your post about using it with external ZnSe lens. In any case I don't think it uses germanium lens.