Author Topic: laser spot thermometer measuring temp of laser spot itself - possible?  (Read 1465 times)

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Offline calel

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ok I feel this is even more scifi than the other topic  :palm: but here we go

a laser spot thermometer that measures the temp of the exact spot the laser is pointing at (as opposed to slightly above or below the red spot, depending if IR receiver lens is above or below the laser emitter)

so again a parallax-free config, basically a single-lens spot thermometer where the lens would have to - somehow - emit a visible red laser while also receiving IR, all in the same "line of sight"

this would enable perfect accuracy since what you're pointing at is precisely what you're measuring, regardless of target distance - in theory is that even possible?

 

Online Fraser

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #1 on: October 13, 2020, 09:11:39 pm »
Yes it is possible. As I detailed in my other response, Raytek specialise in such IR thermometers. Some provide visible light viewing through the middle of the Germanium lens by using a coaxial lens design. They also offer a “laser through the lens” alternative that fires a red laser through a Germanium coaxial lens with a clear section at the centre.

Fraser
« Last Edit: October 13, 2020, 09:41:02 pm by Fraser »
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Offline calel

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #3 on: October 13, 2020, 09:21:40 pm »
Yes it is possible. As I detailed in my other response, Raytek specialise in such IR thermometers. Some provide visible light viewing through the missile of the Germanium lens by using a coaxial lens design. They also offer a “laser through the lens” alternative that fires a red laser through a Germanium coaxial lens with a clear section at the centre.

Fraser
ok I thought those thermometers you referenced didn't have red a laser pointer (so basically  "receiver-only" thermometers without the red spot emitter)

but how's that even possible? if the laser emitter's behind the IR sensor, then the IR sensor will just block the laser, so no red spot. and if the laser pointer's in front of the IR sensor then it will block the incoming IR signal, so no IR pocture ???
 

Online Fraser

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #4 on: October 13, 2020, 09:29:18 pm »
It is just optics. Mirrors or prisms may be used to steer the light around any thermal sensor.
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Online Fraser

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #5 on: October 13, 2020, 09:33:26 pm »
I use ‘through the lens’ IR thermometers that have a target reticle in the viewfinder with a small circle at the centre. Whatever fills the circle when a scene is viewed is the area being measured. Superb bits of kit, but expensive. My favourite is a Minolta TA-0510 Auto Focus unit shown in the last few pictures below. I had to import mine from Japan.

Fraser
« Last Edit: October 13, 2020, 09:41:59 pm by Fraser »
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Offline calel

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #6 on: October 13, 2020, 09:43:28 pm »
It is just optics. Mirrors or prisms may be used to steer the light around any thermal sensor.
I see

so basically there will be some loss of signals (diminished amplitude)? like the red laser spot will be less bright, and the IR picture more "dim"?
 

Online Fraser

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #7 on: October 13, 2020, 10:18:15 pm »
For anyone interested in TTL IR thermometers I attach some images I just took of two units that I use. The Minolta  Land Cyclops is quite common on eBay, but is a cost reduced model. The Minolta TA-510 is ‘High end’ model with auto focus. It is worth comparing the optics of the two models. The TA-510 passes both it’s thermal and visible light energy through a transparent window. How is this possible some may ask...... well I must leave you something to discover for yourself rather than spoon feed Knowledge to you  ;)

In the example I used a large Teddy Bear called Conrad as the target. The room lighting is not bright and positioning the iPad correctly behind the optical viewfinder was a little challenging whilst holding the IR thermometer ! The Cyclops exit pupil size is very small.

Fraser
« Last Edit: October 13, 2020, 10:50:02 pm by Fraser »
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Online Fraser

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #8 on: October 13, 2020, 10:20:18 pm »
The uncompressed images through the viewfinders.....

The target is the same distance from the IR thermometer in both cases. The TA-510 has true auto focus optics whilst the Cyclops is fixed focus optics.
« Last Edit: October 13, 2020, 10:23:56 pm by Fraser »
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Online Fraser

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #9 on: October 13, 2020, 10:40:59 pm »
Some Patents that are worth studying  ;)

https://patents.google.com/patent/US4634294

https://patentimages.storage.googleapis.com/3a/d1/4c/62814e9c51b7c6/US20130051424A1.pdf

When you do not know how something works, it can be helpful to Google for Patents on known products and if they are not known, Google the question and sift the results  :-+

Fraser
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Online Fraser

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #10 on: October 13, 2020, 11:07:13 pm »
The Optical design used in the Minolta IR thermometers. Where a visible light scene may pass in one direction, a similar optical system may pass a laser in the opposite direction.

https://associationofanaesthetists-publications.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2044.1989.tb11289.x

Fraser
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Offline CatalinaWOW

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #11 on: October 14, 2020, 02:21:22 am »
It is just optics. Mirrors or prisms may be used to steer the light around any thermal sensor.
I see

so basically there will be some loss of signals (diminished amplitude)? like the red laser spot will be less bright, and the IR picture more "dim"?

In some sense you are correct.  Either some area of the infrared receiver is lost or some light transmission is lost.  But in a properly designed system these losses are negligible.   The simplest way to think about this is the area loss case.  Any loss in area is easily compensated by a slightly larger aperture.  And a visible pointing beam consumes only a small fraction of a cm^2 in area.
 

Offline mzzj

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #12 on: October 19, 2020, 05:02:02 am »
For anyone interested in TTL IR thermometers I attach some images I just took of two units that I use. The Minolta  Land Cyclops is quite common on eBay, but is a cost reduced model. The Minolta TA-510 is ‘High end’ model with auto focus.
Cyclops 300AF has also autofocus and they go sometimes for peanuts on ebay.

They seem to drift low with age but luckily adjustment procedure is reasonably simple.
 

Offline alexwhittemore

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #13 on: October 19, 2020, 09:17:39 pm »
Just throwing this out there, I'd be willing to bet building your own isn't even that hard. Germanium is opaque or reflective to visible light, yet transparent for LWIR. The same zero-power germanium window you might use as coverglass to protect a thermal camera will happily reflect a visible laser dot. Just build a little teleprompter-style hood to hold the coverglass (covergermanium?) at a 45 degree angle in front of the thermal imager's lens, then fire a red laser at it from the side. Laser dot directly on the center crosshairs of your imager, no parallax.

Of course, feel free to substitute the imager for a spot IR thermometer, that would work just fine as well. The only issue with that is EVERY IR thermometer has a field of view. So it's not as though you can measure ONLY the laser dot. It'll be the average over a few arcseconds around that dot.

I happened to be looking yesterday - germanium windows of useful size go for like $50 used on ebay.
 

Offline Bill W

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #14 on: October 20, 2020, 10:51:28 am »
The only issue with that is EVERY IR thermometer has a field of view. So it's not as though you can measure ONLY the laser dot. It'll be the average over a few arcseconds around that dot.

Some of the better ones give you a ring of laser dots to show the measurement circle rather than a single dot.  A lot more optics involved to produce those of course.

Bill

Online Fraser

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #15 on: October 20, 2020, 12:50:19 pm »
This thread actually provides the reason why thermal imaging systems have become so popular as their price has reduced. The IR thermometer was a common, and affordable, way to measure a target surfaces temperature without contact. There were some rules for obtaining decent accuracy though. The target surface Emissivity should be known, or estimated using Emissivity tables, and the target surface should fill the IR thermometers field of view.

If the Emissivity is incorrectly set on the IR thermometer, an error will be introduced into the measurement. If the target surface does not fill the IR viewers FOV, the average of the target and surrounding surface or background will be measured and this can result in significant measurement errors. Measuring a surface of uneven Emissivity will also introduce an error. The quality and specification of the IR thermometer dictates its accuracy and can influence the measuring spot size at various distances. The spot size to distance ratio is normally detailed in the specification and a smaller spot size for a given distance is needed where a target is small. Cheap IR thermometers tend to use a single fresnel lens or no lens at all and they can have very poor spot size to distance ratios. High quality IR thermometers designed to provide very small spot sizes at significant distances are often built with high quality, expensive, optics so cost more to purchase.

Thermal imaging cameras provide the user with an array of spot temperature measurements from which to select those associated with the region of interest using the spot measurement function. As such the thermal scene provides more information on the target area and its surroundings. Even low resolution 16 x 16 pixel thermal arrays can provide decent target measurement where the user can see that they are selecting only the pixels that are illuminated by the target area. Greater thermal sensor resolution can provide more pixel coverage of the target area, depending upon the optical systems specifications. IFOV comes into play here.

In thermal imaging, the context of the thermal scene image when compared to the users visible light view of the scene can significantly aid a better understanding of the thermal energy distribution and any anomalies present. A classic example used in advertising is a utility mains breaker board where a thermal imaging camera can clearly show a breaker or contactor that is suffering an overload or failure condition. To achieve the same with an IR thermometer, a model with the correct spot size to distance ratio should be selected to differentiate between breakers or contactors and the IR thermometer is carefully scanned across the target panel looking for anomalies. The human brain tracks the temperatures measured and maps then against the area of the panel highlighted by the laser spot indicator. If an anomaly is detected, the user can move closer to the target panel to better localise the issue. That does take the user closer to potential danger however (In the case of High energy systems)

How much simpler it is to use the thermal camera, with a decent specification, to view the panel from a safe working distance and actually see the variance in temperature across the thermal scene, this enables the user to see the thermal average of a scene and areas that are either hotter or cooler than the surrounding ‘reference’ areas. Hard to achieve with a single pixel IR Thermometer.

Out of this thermal imaging advantage some more affordable thermal imaging tools were born. IRISYS (UK) were manufacturing RedEye thermopile arrays at low cost for people counting devices that they produced. These Thermopile arrays started out as 16 x 16 pixel devices but 32 x 32 and 47 x 47 pixel models followed. With such low Native resolution arrays, interpolation was used to create acceptable thermal images. The RedEye thermopile device was then married up with a VGA visible light camera in a handheld design and the images combined using thermal-visible light scene fusion. The visible light image provided scene context and the low resolution thermal scene overlay provided the scenes thermal profile, albeit at low resolution so quite large IFOV on target. The Visual Thermometer was born ! The two models made by IRISYS were the VT02 (16x16 pixels) and VT04 (32 x 32 pixels). I own a couple of the original VT02 prototypes in the original IRISYS red cases. The visual thermometer was an interesting idea and FLUKE bought IRISYS.  The VT serieswere sold as an affordable thermal imaging device for the trade etc. Sadly the timing was not great as the FLIR Lepton and Seek Thermal cores were soon released and basically placed the low resolution VT series ‘in the shade’. The far greater resolution of the seek and a FLIR offerings made affordable thermal imaging cameras a reality for the masses.

FLIR has not ignored the appeal of the simple Visual Thermometer though. They have a range of devices that use the 80 x 60 pixel Lepton core as a Visual Thermometer or thermal viewer that competes directly with FLUKE’s VT series. FLIR want their toe in every market, including any, and all, that FLUKE are present in. There have been some interesting work done by FLIR on low end visual thermometers for users who neither need the capabilities of a ‘full’ industrial thermal camera or have the appetite for its relatively high price tag. A hybrid Single pixel Thermopile IR thermometer with Lepton 80 x 60 pixel thermal camera was born ! It is a weird beast that measures temperature using conventional IR thermometer technology, yet provides a thermal scene for context on its display using the lepton core. The Lepton is not the most accurate measurement device so maybe FLIR decided the IR thermometer provided a more accurate measurement system ? it brings with it the issue of spot size to distance ratio though  :(

I attach pictures of the ‘hybrid’ TG165 visual IR thermometer.

Fraser
« Last Edit: October 20, 2020, 01:53:21 pm by Fraser »
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Online Johnny10

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #16 on: October 20, 2020, 02:13:25 pm »
Very Interesting.
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Online Fraser

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #17 on: October 20, 2020, 02:56:58 pm »
The IRISYS Visual Thermometer story and Teardown is to be found here......

https://www.eevblog.com/forum/thermal-imaging/fluke-vt02-thermal-camera-visual-thermometer-teardown/

Fraser
« Last Edit: October 20, 2020, 02:59:52 pm by Fraser »
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Online Fraser

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #18 on: October 20, 2020, 04:07:38 pm »
The Extech IRC130 hybrid IR thermometer-camera tries to show the user the area where the IR thermometer thermal measurement is taking place with a projected Ring and centre dot laser. Picture attached.

https://www.tester.co.uk/extech-irc130-thermal-imager-ir-thermometer-with-msx-8-7hz?gclid=CjwKCAjwlbr8BRA0EiwAnt4MTiCOlRvFUx9183uJzb7piVxdN2Qgl4JplQEqHtACYg5Hw7mU-fv0ZRoC2RAQAvD_BwE
« Last Edit: October 20, 2020, 04:24:04 pm by Fraser »
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Offline calel

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #19 on: October 20, 2020, 05:01:02 pm »
wait you sure those Extech & Fluke thermometers are parallax-free? cause I see multiple lenses in both those models  ???


anyway since you brought up the TG165 - I recently watched a vid on youtube which revealed the truth behind the TG165 (the fact that it wasn't a true IR camera but just a thermometer which somehow gives the same image as an IR cam. they also said true IR cams are called radiometric cams or something)

so question is, what's the difference & why does it matter? I mean whether it's a real or false IR cam, as long as there's this coloured red/yellow/blue image representing cold & hot zones, then it's the same thing right? only the result matters
 

Online Fraser

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #20 on: October 20, 2020, 05:30:46 pm »
Calel,

The IRISYS/FLUKE VT series and Extech IRC130 do indeed have multiple lenses and will suffer some degree of parallax error between the thermal measurement point and visible light images. Whether the parallax error is significant in the intended applications is open to debate. This is not a rifle sight after all !

The units that present a reasonable thermal scene resolution can show the user the relative temperatures in the observed area. If a Radiometric Core is installed in the unit, it can measure locations within the scene. The units that use non radiometric cores and use an IR thermometer module adjacent to the camera are...... how shall I say this nicely....... unusual beasts ! I personally do not see why FLIR designed such an unusual hybrid when a Radiometric Lepton is more than capable of meeting the needs of a simple visual thermometer. This can clearly be seen in the FLIR simple thermal camera lineup in the TG series. Picture attached.

To me, the TG165 is a “Frankenstein’s monster” and having spoken with someone who was on the design team, I have to wonder whether the teams terms of reference were adequately detailed by management !

A thermal camera is anything that can collect thermal energy from a scene and present that thermal energy in a display of some kind that correctly represents the scenes thermal profile. The term Visual Thermometer was introduced by IRISYS because they were using a very low resolution 16x16 pixel thermopile array that is, truthfully, incapable of presenting the user with enough detail to provide context to the observed scene. That is why a visible light camera was used to collect contextual information for fusion with the crude thermal ‘blob’ display. It was amazing what was achieved with only 16x16 pixels, plus interpolation, but IRISYS were nervous about calling the unit a “Thermal Camera” in the current market. They did call the earlier 16x16 pixel based imagers “thermal cameras” but, as anyone who used one knows, they met a need but cannot be compared to the image quality produced by a FLIR Lepton or Seek Thermal core.

The FLIR Lepton and Seek Thermal cores may not be as capable in some respects as the more expensive cores that are used in more sophisticated cameras, but they still have their place in the market and still deserve to be considered versatile thermal camera cores  :-+

Finally, if a device uses a FLIR Lepton or a Seek Thermal core to present a user with a thermal scene, it is, in my opinion, a “Thermal Imaging Camera”. No doubt about it. If the same core were used in some automated fire sensor system or temperature monitoring device, that does not present the user with a thermal scene, there would be a fair argument that the core was working as a multi pixel sensor array, rather than a true camera. Some may say that if a unit cannot store an image, it is not a “camera” and is a “viewer”. Just semantics in reality though.

« Last Edit: October 20, 2020, 05:35:57 pm by Fraser »
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Offline calel

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #21 on: October 20, 2020, 06:49:17 pm »
amrite so I'm still confused about the difference  :-\ but basically radiometric is superior to spot? no advantages of the latter over the former?


and the TG165 is only a visual non-radiometric thermometer? I've noticed that the TG line only go up to 160x120 (with the TG297) is that because of an inherent limitation of visual thermometers?
 ie. is it possible or not to have a 320x240 spot (non-radiometric) cam?
 

Online Fraser

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #22 on: October 20, 2020, 07:15:56 pm »
Read my posts again slowly and I detailed the differences  ;)

For information....

1. Radiometric imaging Cores have the ability to output the measured temperature of any pixel in the imaging array. The whole thermal scenes pixel values can often be saved as well for later analysis.
2. Non-Radiometric imaging Cores can provide a nice thermal image of a scene but the cores manufacturer does not permit access to all of the pixels temperature data. They sometimes provided a Temperature measurement from a small centre grouping of pixels.
3. Spot temperature measurement can mean many things. On a thermal imaging camera it can mean a fixed or moveable small group of pixels that are read out for temperature measurement. There can be more than one moveable spot measurement area on more capable cameras. On an IR Thermometer there is only a single measurement pixel so only one spot measurement that can be of significantly larger area on the target than that of a thermal camera.


Regarding your last questions.....

The TG165 uses a non-Radiometric Lepton 80x60 pixel imaging core. The temperature measurement role is carried out by the IR Thermometer part of the camera.

The term “Visual Thermometer” is just a name. Do not get caught up in that description. It is what the equipment is capable of imaging and measuring that characterise it and not a name given to it by a marketing department !

Yes you could have a 320x240 “Visual Thermometer” with single spot measurement capability. The FLIR Lepton 3 used in the better TG series cameras is the highest resolution Lepton available at 160 x 120 pixels so another imaging core would be needed. Seek Thermal offer a QVGA+ resolution core and the QVGA+ Seek Reveal Pro offers measurement capability.
« Last Edit: October 20, 2020, 07:30:23 pm by Fraser »
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Offline calel

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #23 on: October 20, 2020, 07:51:53 pm »
ok

 is there any conceivable situation where a non-radiometric cam is preferable over a radiometric cam?
 

Online Fraser

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Re: laser spot thermometer measuring temp of laser spot itself - possible?
« Reply #24 on: October 20, 2020, 08:05:58 pm »
No
« Last Edit: October 20, 2020, 08:08:12 pm by Fraser »
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