Economy thermal imager?

from

where

Thermal imagers are getting cheaper, and will continue to do so, I hope. Sub-$1000 one of these days maybe. Even a 100x100 pixel imager, maybe with a plastic lens, could be mighty useful.

Our FLIR cost about $10K a couple of years ago and it was worth it.

ftp://jjlarkin.lmi.net/IR_0026.jpg

ftp://jjlarkin.lmi.net/IR_0032.jpg

John

Mikron. More pricey, but an order of magnitude better instrument.

Harbor freight has about five different sense model, but I wouldn't be surprised if a cheap Chinese model didn't show up eventually.

Back when all there was was what we had, and that was only 4 fps and ran on a 386, and had no out to NTSC option that we could even record from... it was $90k+

At the same time, Fischer Price sold a B&W "toy" camera for $150 that could have a Ge or Pyrex lens or filter put on it, and it would do IR very nicely.

We all thought that was pretty funny, thinking how mere color added $89.9k to the price.

Well... that and a nice arrangement with a little cup of Liquid Nitrogen. It was a real thermal imager.

Now, they have room temp jobs. Your $10k unit is cheap by comparison. The industry sure has come a long way since '87. I'll bet you could get a real nice one from Kikron. Those ones with the LCD "flap" in the back... They looked nice. Likely about $7k though. Still a very REAL instrument, where some seem more like an "also show" to the party. Quantifying accurately should be a requisite. Mikron does that well. Not sure about some I've seen. I am sure that FLIR also does nice, and true (as it were) instruments.

There are some though that are wide in their accuracy window, and calibration seems and end to end thing, instead of being corrected along the entire scale. Mikron sells nice Black Body calibration sources too. Many can be made NIST traceable.

I still find it funny that I used to dope up a basketball with high temp silica "plaster of Paris", then wrap nichrome coils around that, then more "plaster". Then slice the sphere in half to get the ball back out. Reform the sphere. bake it all. and add a radiation port to it (a ceramic tube). Surround the outside with fire brick used for kilns. Suspend all that in a big rack with the tube pointing out the front.

Add about 2500 Watts, a line cord (X Large) and a pid controller,and you have a precision black body source that can make about 4000 degrees F inside the globe. Those high temp sources are far more precise. They vary little. A small black body source that uses a painted surface (which they also sell) is harder to keep a uniform temp across it. They have FLIR calibration sources now that are cool (hot) and stable across a huge surface, which is very hard to do.

Mikron Or their parent, has also seemingly found a way to get better IR focus than others.They have some pretty crisp detail going. I do not know if you looked at the pdfs or not.

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thermograms is what you referring to...... cmos and ccd found in digital cameras are only sensitive to the NON-Thermal or NIR.

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IIRC many common soldering irons run in the 600 F to 700 F range (not all that far from visible glow) and may well output enough for a modified digicam. I swear, that as child i could see the soldering iron by its own glow (in the middle of the night when i woke for some reason) some night when i left it plugged in.

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The peak wavelength for a black body radiator is simply inversely proportional to the absolute temperature. At 6000 K (e.g. the Sun) the maximum wavelength is about 0.5 um (yellow). The silicon camera sensors have some kind of response to 2-3 um, corresponding to 1500 ..

1000 K. Humans and room temperature furniture are around 300 K, thus the radiation peak is around 10 um, thus, ordinary glass is not very transparent and ordinary silicon cells are useless.

The radiation drops quite quickly, when going from the peak towards shorter wavelengths, but still this explains why the eye (400-700 nm response) can detect some weak dark reddish radiation from object with only 1000 K temperature (black body radiation peak at 3000 nm).

Paul

"JosephKK" wrote in news: snipped-for-privacy@4ax.com:

I believe it. I've seen them at times. I can't tell when sight ends and imagination begins though, I tried.. >:) I have a nice temperature controlled iron now so I'll try this again some time. Helps to try to see it with the rods, not the cones, so at least thirty degrees to the side.

Paul Keinanen wrote in news: snipped-for-privacy@4ax.com:

? 727°C? I remember from pottery classes in school that you get into a fierce cherry red by that high. Nice confirmation here:

White light at 1200 C? What a maroon. I think she applied the conversion table backwards. Tungsten bulbs run 2800-3300 K.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

Phil Hobbs wrote in news:7vednQzvUYfK1eHXnZ2dnUVZ snipped-for-privacy@supernews.com:

I didn't think much about it. That temp would look yellow I think. The red is right though. I remember being taught to gauge the temperature of a pottery kiln by the colour. There are even little gauges used for furnaces that are adjusted till a small element fades to a match with the backgound colour, and a reading is made of the temperature that way. I think some slack can be cut re that white. It's wrong, but look at all the colours that pass for white. You can stick a load of video monitors together in a room and see greater errors than hers.

Nowhere close. You don't even get out of the deep reds until 1500 K or so.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

Phil Hobbs wrote in news:Y4GdnXaF4Y0CGeHXnZ2dnUVZ snipped-for-privacy@supernews.com:

Or you could try this one:

303px-PlanckianLocus.png

That shows you can follow the curve right down to around 800K and still expect to see visible red. The only difference is that they resolve a tad deeper into the red end.

This one shows that it's a matter of how much visible red, not whether it's there or not:

In a furnace there's a lot of energy, even a 'cool' one has enough visible red to see it.

So it's a question of how much, and also how sensitive we are to it.. Red is the largest perceived part of the visible sprectrum, I mean it covers more actual nanometres than the other colours, by far, and when looking at furnace colours we're not looking at a single line either, which is why I posted that second link. Also, we're likely to compare the red against a dark background. (kiln view ports are designed to exclude external light).

Putting it another way, take a small butane flame with inducted air (blue sharp-tipped flame), it can just about reach 1500K and will melt a copper wire (ignoring flame colour) with a orangey-yellow ball forming at the end, but if you try to put that copper on a red hot cooker ring it just sits there oxidising. The ring IS evidently glowing a strong cherry red, but it's not anything like the 1356.6K needed to melt copper. And yes, I have thought of poor thermal transfer there, but I've seen overheated copper soldering iron bits glowing, but not melting.

I'm sure a lot of this is very subjective but it's still true. That subjectivity is why the hot-wire gauge is used to make simple meaures of furnace temperature. A 'red' that glows against one hot glowing body will look black against another brighter one. And within that very broad range you'll likely find that every one of them appears red to someone.

Basically even a deep red looks cherry red if you have enough of it and nothing for it to compete with..

Lostgallifreyan wrote in news:Xns9C60E3699100Azoodlewurdle@216.196.109.145:

Meant hotter, not brighter.. (and darker, rather than 'black')

Lostgallifreyan wrote in news:Xns9C60E6D33A5F5zoodlewurdle@216.196.109.145:

And just to show how it can't really be said to be either right or wrong, what colour IS 'cherry' red? Some of them look deeper and darker than the little red spot seen in a bare IR laser diode... The dark ones taste better too.

What color temperature is maroon? I bet her face is red.

John

The human eye is very bad in detecting absolute colours, due to the "automatic white balance adjustment" so you really need a reference chart at the same illumination level to reliably compare colours.

Apparently the Draper point at 798 K seems to be some standard for visibility of hot objects, but I have not found any references how this is actually determined.

To get a good general overview how the radiation behaves on short wavelengths, it is a good idea to plot the black body radiation on a log/log scale, e.g. figure 10 in

Look at the 800 K (Draper point) curve, which has a peak at about 3,5 um and look at intensity at 0.7 um (the nominal limit of human vision), the magnitude is about 5 orders of magnitude (50 dB) below the peak.

At 1500 K, the peak is at 2 um and the intensity drops only 1.5 orders of magnitude (15 dB) at 0.7 um but the absolute level at 0,7 um is 5 levels of magnitude (50 dB) above the value for 800 K at that wavelength.

Compare this with the sensitivity of the eye

For normal illumination levels (photopic vision) the nominal 700 nm limit is somewhat arbitrary, since the sensitivity is doubled (+ 3 dB) every 10 nm when going from 770 nm down to 670 nm, a total increase about 30 dB. In that wavelength band the 800 K black body radiation intensity drops about 12 dB and the 1500 K radiation drops about 5 dB in that region, so the stimulus is strongest near the shortest end (670 nm) of that band.

However, the absolute level of 800 K and colder objects is very low and a dark adapted eye (scotoptic vision) is required, however the eye is insensitive to deepest red at these levels. Practical values starting at 700 nm and the response doubling every 10 nm down to about

580 nm.

The scotopic vision is of course black and white and if in a dark room an object is heated, a glow will be observed, when there is sufficient power below about 700 nm, but you can just tell that something is glowing, but you can not determinate the colour due to the scotopic vision.

When the temperature is further increased, the absolute power levels below 770 nm are increased significantly and sooner or later the photopic vision will be smoothly activated and it becomes possible to determine colours.

The level at which the transition occurs, depends of the absolute level reaching the eye and hence also of the angle of view.

Paul

Paul Keinanen wrote in news: snipped-for-privacy@4ax.com:

That's what I was getting at (rather verbosely). That and the fact that cherries actually have so many colour variants you can plot most of the visible black body spectrum with them. :)

Paul Keinanen wrote in news: snipped-for-privacy@4ax.com:

That's interesting because when I looked at that page I saw I was apparently wrong when I said that to spot a dimly glowing overheated soldering iron bit it helps to use the scotopic vision. It IS less sensitive to light at longwave red. Even so it did seem to help, and your comment that scotopic vison is needed seems to back this up. Maybe it has more to do with the effort of trying to see it, balancing the two types of vision by arranging the object at certain angles to our centre of vision. Maybe our brains can make more of it by this comparison than by either type of vision alone.

Anyway, looking at the rest of what you wrote, it seems that a claim to see a glow from something as 'cool' as 500°C is viable (though the standard you mentioned states 10° higher), if seen in darkness. I thought I'd managed it at 450°C once but I'm not prepared to back that up. Next time I have a controlled way to set that temperature I'll try it. I did once try this with a kiln observation hole but I can't remember what the temperature was when it became visible. It was thirty years ago, and I think I got distracted and revisited the kiln too late to see the first light anyway.

It has a couple of references if you want more info.

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