Got an idea for a thermal imager mod to standard CCD security camera

[Ben321]

I just thought of this right now. Not sure how well this would actually work, but I got this idea for modifying a standard monochrome CCD security camera. First of all, it must be monochrome, as color one-chip cameras always have a Bayer CFA (color filter array) bonded to the surface of the silicon CCD sensor itself. The idea I have is to use the tempurature dependent noise of a CCD to perform thermal imaging. When a CCD is hot, it puts out more dark-current (a signal that exists even when no light is falling on the CCD). Pixels that are warmer produce more dark-current. That is, the noise is stronger on pixels that are warmer. This could be used to form a microbolometer array, out of a standard silicon CCD (no VOx, no amorphous silicon, no depending on other companies using special manufacturing techniques). In fact, it should be a simple modification for an ordinary hobbyist to perform, and should let you turn an ordinary cheap monochrome CCD security camera into a thermal imager. The modification is simple. The actual process simply involves removing the glass protective cover on the CCD chip itself (hardest step, as it must be done VERY carefully, even slight damage to the silicon underneath could destroy the chip), as well as converting a standard C-mount security camera lens from containing glass (or plastic) elements into one containing a germanium element of the same focal length as the original elements. This is nececary, because germanium not only passes LWIR, but also blocks visible light. Focussed LWIR light coming through the germanium lens will heat the silicon CCD surface in a pattern that corresponds to the thermal image. Thus the noise-levels from the CCD's pixels will be a thermal image.

Here is a diagram that includes more detail on performing the steps of the modification.

[joe-c]

i know that a ccd (or cmos?) without protection glass can be used as detector for alpha radiation. i have seen it long time ago.

but i don't think it works for thermography. on a CCD the light will in-case a charge, this can be read. but thermal radiation don't incase the charge, it just warmup your chip. that's why bolometers has pixels with micro bridges to isolate the heat from the neighborhood.

but with a NIR filter it should be possible to see temperatures above 400°C.

[Fraser]

Ben321,

In the early days of IR imaging there were experiments with wavelength translators that converted light energy of one wavelength to another, In that case NIR wavelengths to visible light wavelengths for viewing with an image intensifier or sensitive vidicon camera tube.

The Pyro-electric vidicon tube (Pevicon) may interest you The tube was basically a standard format Vidicon tube used in CCTV that had a special target material that responded to thermal energy. The target was read with the electron beam in the same way as a standard vidicon target is read. In this way a thermal image could be created using electronics very similar to that found in CCTV cameras of the era. Ground breaking stuff at the time.

That was some lateral thinking on the part of those who developed the Pevicon Tube (English Electric Valve company aka EEV)

If you could find a suitable material that converted thermal energy into IR or visible emissions you could use such with a CCD or CMOS unfiltered sensor to create a thermally responsive sensor array. The camera arrays in my high resolution X-Ray machines use a scintillator plate in front of what is basically a huge CCD imaging chip so not that dissimilar to that which I described above.

Your problem would be in finding such a suitable Thermal Energy to IR or visible light energy conversion material. Such is not a trivial matter. There is thermally responsive LCD material but it has a narrow operating range set by its manufacture.

I applaud your desire to invent a new thermal imaging approach but it is not going to be simple as some very clever people were trying to do the same as you prior to the invention of the microbolometer and BST sensors.

Do not discount mechanical scanning camera designs. When only a single pixel thermal detector was available, the camera designers used horizontal and vertical servo driven mirrors to present the thermal scene to the detector pixels and created a raster scan. Sadly the mechanics and mirrors are both expensive and specialist items. I considered converting one of my old scanning type cameras to use a modern Melexis thermal sensor but I do not really have the need for such a project so never developed it. Scanning thermal cameras are often to be found cheaply on ebay. Look for AGA and AGEMA thermal cameras. Pictures of my AGEMA 880 scanning camera and optical path attached.

Fraser

[Ben321]

The idea here is that a characteristic that is usually not desirable (increase in noise in image, with increase in temperature of the CCD) could actually be a desirable trait, if one cares to actually use it to sense temperature. Also, remember how it was mentioned on these forums before that the choice of silicon for the lens material in the FLIR One is not an ideal material? The reason is that silicon tends to absorb LWIR instead of transmitting it. And of course, since absorbed LWIR energy turns into heat, silicon tends to get hot (temperature increases) when exposed to LWIR radiation. That makes a silicon CCD the perfect sensor for creating a home-brew thermal imager. All you need to do is keep 100% of visible light and NIR light (wavelengths that have a photoelectric effect on silicon) from reaching it. And that's where the cheap germanium lenses that you can buy on eBay come in handy. Not only do they block visible and NIR light, they also transmit LWIR light (the desired wavelength range) and focus it. As long as you don't have a glass protector plate in front of the silicon surface of the CCD, the CCD itself should absorb the incoming focused LWIR light and heat up in the pattern of the projected LWIR image. That heat pattern turns into a noise-level pattern on the pixels of the CCD chip. If you take a one-minute long video of a stationary scene, and then later take that video file and load it into software to split the video into frames and sum the frames together (software-based video frame integration), you will resolve the noise pattern (a single frame contains only noise in that instant, but a sum of many frames reveals the noise pattern, which in this case is a thermal image). The sum of a full minute of video frames (30fps * 60 seconds = 1800 frames), should EASILY reveal the noise pattern (the thermal image).

Of course there is another source of noise, and that's truly random noise, and of course there are other patterns in the noise (other than the thermal pattern) such as variations in the sensitivity of the different pixels. To compensate for these non-thermal noise effects, you will need two 1-minute long exposures (1 minute long videos who's 8-bit frames have been summed in software to produce a high-bitdepth image file). One will be taken of a thermally flat object, and the other of the desired thermal scene. The noise sources in each image are as follows.

Thermally flat object image contains the noise pattern from:
thermally flat object + sensitivity variations throughout the CCD chip
Let's call this image "A"

Desired scene image contains the noise pattern from:
desired scene + sensitivity variations throughout the CCD chip
Let's call this image "B"

B - A = C

Image C contains the noise pattern from:
desired scene - thermally flat object

Since the thermally flat object can be approximated as a constant, you just need to add that constant to all of the pixel values.
C + constant = D

D is the desired image, and contains ONLY the thermal noise-level pattern associated with the desired scene.

How do you know what the constant is? Well you can't know it exactly, because for that you would need to know all the physical properties of the CCD chip itself as well as what the exact temperature of the thermally flat object, in order to empirically derive this constant. However you CAN easily find a constant that produces a displayable image. As long as you aren't going to try to actually measure the Kelvin temperatures in the scene, and only care about using this technique to create a thermal image for viewing purposes, the exact value of this constant doesn't matter. In this case, you can simply select a value for the constant that makes sure that none of the pixel values drops into the negative range (for display on a monitor, negative numbers are invalid). In this case, the constant that you need to add is simply the inverse of the lowest value in the image. If the lowest value in the image is -100, you add 100. If the lowest value in the image is 20, you add -20. This guaranties that the lowest value in the thermal image ALWAYS corresponds EXACTLY to the color black in the displayed image.

After that step of adding the constant, you need to make sure that the maximum value can never exceed 255 (the highest value that can be displayed on a computer monitor).  To do that, there are a couple techniques. You can clip it (all pixels >255 get set to 255). Or you can scale it to fit (PixelOut = PixelIn / MaxPixelValueInImage * 255).

The end result should be an actual thermal image that should be able to be clearly seen on a computer monitor.

[bap2703]

You are heating a solid piece from a quite thermaly conductive material : the noisy image will also be blurry.
Plus air contact with the material should not help.

As more or less already explained FLIR is probably rapping our wallets for some good reason.

[bktemp]

You are heating a solid piece from a quite thermaly conductive material : the noisy image will also be blurry.
Plus air contact with the material should not help.

This is why it won't work.

Look at how microbolometers are built (vacuum chamber + actual sensors floating in front of the sensor die).
CCD/CMOS sensors instead are designed to have a good thermal conductivity to make all pixels equally hot for beeing able to compensate for some temperatur effecty by using black dummy pixels surrounding the active sensor area.

[Bill W]

So we have the 1/60th Hz camera with a NETD of about 100K, and it still needs a germanium lens.
 
Those interested might like to google for 'RedShift' patents.

Here is a more viable plan for your cheap camera to undercut FLIR Ben:
How about soldering an array of 80x60  0402 10k thermistors to a PCB and then measure their resistance with a DVM, put the numbers into a spreadsheet and generate an image that way.  Save even more by using a pinhole lens.

[Ben321]

You are heating a solid piece from a quite thermaly conductive material : the noisy image will also be blurry.
Plus air contact with the material should not help.

As more or less already explained FLIR is probably rapping our wallets for some good reason.

So that means the temperature difference between adjacent pixels will be very small, but it will still be there. And that's another reason for a long integration time (notice I said 1 minute, not 5 seconds, in my description of the possible mod). As long as the object being imaged is stationary, this should pose no problem, and the 1 minute exposure should reduce the S/N ratio to the point that the difference between adjacent pixel thermal signals is larger than the difference between adjacent pixel random noise signals. This will make it so that after processing in software (thermal flat subtraction, followed by scaling values to be between 0 and 255), there will be an actual thermal image that can be seen. Will probably be quite noisy, but it will still be easily seen.

And that may be the only way to get a 640x480 thermal imager of any kind or image quality, for less than $4000 (currently FLIR Vue 640 costs $4000, and I've seen nothing cheaper). In fact, the parts for my mod, if bought from eBay, should cost under $500.

[bktemp]

So that means the temperature difference between adjacent pixels will be very small, but it will still be there. And that's another reason for a long integration time (notice I said 1 minute, not 5 seconds, in my description of the possible mod).

If you wait for a long time, all pixels will have the same temperature. The integration time must be as short as possible to reduce the heating of adjacent pixels. But this results in a zero S/N ratio.

And that may be the only way to get a 640x480 thermal imager of any kind or image quality, for less than $4000 (currently FLIR Vue 640 costs $4000, and I've seen nothing cheaper). In fact, the parts for my mod, if bought from eBay, should cost under $500.

The best way of getting a cheap high resolution thermal imager is the scanning type Fraser has described.
It has already been done:
https://www.eevblog.com/forum/thermal-imaging/diy-pinhole-thermal-camera/

[Ben321]

Do not discount mechanical scanning camera designs. When only a single pixel thermal detector was available, the camera designers used horizontal and vertical servo driven mirrors to present the thermal scene to the detector pixels and created a raster scan. Sadly the mechanics and mirrors are both expensive and specialist items. I considered converting one of my old scanning type cameras to use a modern Melexis thermal sensor but I do not really have the need for such a project so never developed it. Scanning thermal cameras are often to be found cheaply on ebay. Look for AGA and AGEMA thermal cameras. Pictures of my AGEMA 880 scanning camera and optical path attached.

Fraser

Problem with these are an older technology, and not only did they not have array-type sensors back then (so they had to scan), they also used less efficient sensor material, which meant liquid nitrogen cooling was required. You need a license to buy liquid nitrogen, because of how dangerous it is, so there's no way that the average person would even be able to get this one critical chemical needed to operate the imager. Therefore there's no way that an ordinary hobbyist like me would even be able to operate the device.

[X]

The idea I have is to use the tempurature dependent noise of a CCD to perform thermal imaging. When a CCD is hot, it puts out more dark-current (a signal that exists even when no light is falling on the CCD). Pixels that are warmer produce more dark-current. That is, the noise is stronger on pixels that are warmer. This could be used to form a microbolometer array, out of a standard silicon CCD (no VOx, no amorphous silicon, no depending on other companies using special manufacturing techniques).

This will not work because there is no thermal isolation between the pixels, they all use the same substrate. The microbolometers typically have the detector material raised up mechanically and isolated from each other.

In fact, it should be a simple modification for an ordinary hobbyist to perform, and should let you turn an ordinary cheap monochrome CCD security camera into a thermal imager. The modification is simple. The actual process simply involves removing the glass protective cover on the CCD chip itself (hardest step, as it must be done VERY carefully, even slight damage to the silicon underneath could destroy the chip), as well as converting a standard C-mount security camera lens from containing glass (or plastic) elements into one containing a germanium element of the same focal length as the original elements.

If you can find a germanium lens for a hobbyist-grade price, I'd love to know where you get it from. The lens is a single crystal of pure germanium, which takes a noble amount of effort to craft. You may as well buy a proper thermal camera for all that effort, and get something that works well.

This is nececary, because germanium not only passes LWIR, but also blocks visible light. Focussed LWIR light coming through the germanium lens will heat the silicon CCD surface in a pattern that corresponds to the thermal image. Thus the noise-levels from the CCD's pixels will be a thermal image.

In a CCD, a bright light source can cause charge to "bleed" into the neighbouring pixels, createing a smear (either horizontal or vertical line) on the image. Also CCDs aren't sensitive to such a long wavelength.

[james_s]

You don't need a license to buy liquid nitrogen, at least not around here. You can pick it up at places that sell industrial gases and welding supplies. Praxair and Airgas are the two big chains I'm familiar with. You do need a proper flask to hold it though, you can't just get a bucket of it.

Sure the scanning systems are less efficient, but compared to trying to use a CCD? The old scanning tech is going to offer orders of magnitude better performance, even something without any cooling.

[KE5FX]

If you can find a germanium lens for a hobbyist-grade price, I'd love to know where you get it from. The lens is a single crystal of pure germanium, which takes a noble amount of effort to craft. You may as well buy a proper thermal camera for all that effort, and get something that works well.

Laser-cutter lenses work very well with IR imagers.  There will be some specific pointers to some in the FLIR E4 thread.  A few dollars on eBay is all it takes.

[Fraser]

My comment on buying a scanning type camera related, not to its normal use, but rather to conversion to use a modern uncooked Melexis sensor in place of the cooled detector and its Dewar. You would need to find a Long WAve scanning camera though as the optics are coated for either Longwave or Shortwave depending upon the detector originally used.

The scanning cameras are often so,d as museum pieces due to their age and need for Liquid Nopitrogen in some cases.

It is a little unfair to say these cameras used. liquid Nitrogen because they used inefficient detectors. It was more about basic physics and band gap noise. The detectors were semiconductor devices made from exotic materials.at room temperature the detector internally generated thermal noise masks any thermal scene related output. When coooled to -196C the internally generated noise is reduced to the point that the thermal scene data is easily read at its output. Some different materials were used to create detectors and arrays that did not need to severe cooling. Namely the AGEMA SPRITE detector that used Lead Selenide and needed cooling to only -70C using a Peltier stack. The later Sterling Cooled (-196C) arrays are amazing. They still produce the best quality, lowest noise imaging in the industry. Due to high cost they tend to be found in scientific applications more than basic industrial environments though. Most satellites thermal imagers are Sterling Cooled as the best noise performance possible is required in that application.

Any thermal sensor system running at room temperature will always be battling with its own internally produced noise. Microbolometers are no different. CCD arrays can be noisy unless Cooled. Hence why astronomers cool them ! DSP and noise reduction algorithms are used to clean up the noise data coming out of the sensor ROIC.

We are indeed lucky that we now have access to thermal cameras that do not have to have Cooled sensors. Cooling usually adds complication, cost and current consumption to a camera design.

Hope this helps understand the Cooled technology a little better.

Fraser

[Ben321]

My comment on buying a scanning type camera related, not to its normal use, but rather to conversion to use a modern uncooked Melexis sensor in place of the cooled detector and its Dewar. You would need to find a Long WAve scanning camera though as the optics are coated for either Longwave or Shortwave depending upon the detector originally used.

The scanning cameras are often so,d as museum pieces due to their age and need for Liquid Nopitrogen in some cases.

It is a little unfair to say these cameras used. liquid Nitrogen because they used inefficient detectors. It was more about basic physics and band gap noise. The detectors were semiconductor devices made from exotic materials.at room temperature the detector internally generated thermal noise masks any thermal scene related output. When coooled to -196C the internally generated noise is reduced to the point that the thermal scene data is easily read at its output. Some different materials were used to create detectors and arrays that did not need to severe cooling. Namely the AGEMA SPRITE detector that used Lead Selenide and needed cooling to only -70C using a Peltier stack. The later Sterling Cooled (-196C) arrays are amazing. They still produce the best quality, lowest noise imaging in the industry. Due to high cost they tend to be found in scientific applications more than basic industrial environments though. Most satellites thermal imagers are Sterling Cooled as the best noise performance possible is required in that application.

Any thermal sensor system running at room temperature will always be battling with its own internally produced noise. Microbolometers are no different. CCD arrays can be noisy unless Cooled. Hence why astronomers cool them ! DSP and noise reduction algorithms are used to clean up the noise data coming out of the sensor ROIC.

We are indeed lucky that we now have access to thermal cameras that do not have to have Cooled sensors. Cooling usually adds complication, cost and current consumption to a camera design.

Hope this helps understand the Cooled technology a little better.

Fraser

Wonder if you could get away with using a LN2 cooled thermal imager at room temperature, if you recorded video from it of a stationary scene/object and then used computer software to integrate the frames of the recorded video file into a single picture? That integration should combat the noise. Or would the noise be so strong that it would overwhelm the signal amplifier in the thermal imager (or at least overwhelm the A/D converter in your TV capture card that was taking in the signal from the thermal imager and digitizing it) preventing any usable video file from being recorded in the first place?

And if such a signal did in fact saturate some of the components in the signal path, would it be possible to compensate by adjusting the offset and range controls? I know that a lot of these old thermal imagers that had a scanning type sensor would also often have 2 knobs for controlling the analog signal. These control knobs were either on the thermal imager head itself or on the control box (which these older thermal imagers usually had, as there was no digital interface to control the camera's functions with a computer). So would it be possible to adjust the offset and range of one of these thermal imagers and get an analog signal (even at room temperature) that stayed within the dynamic range of all the components in the signal path (up to and including the A/D converter in your PC's composite video capture card)? If so, I would think that after recording a video file from this, one could then just average the frames in the resulting video file (add the pixel values of corresponding pixels through all the frames, and then divide the summed pixel values by the number of frames to get the average pixel values), and get a nearly noise-free image.

[Fraser]

Ben321,

The short answer is no.

The detectors simply do not work at rooom temperature !

Fraser

[Ben321]

Are there any scanning type thermal imagers that do NOT require liquid nitrogen cooling? Are there any that use only Peltier TEC for cooling (or even maybe operate without cooling, such as a single-element VOx bolometer sensor)?

[-jeffB]

You need a license to buy liquid nitrogen, because of how dangerous it is

 

Liquid nitrogen is less dangerous in nearly every way than boiling water.

"You need a license to buy liquid nitrogen?" "Germanium isn't worth a lot more than silicon?" Where do you get these ideas?

[KE5FX]

You need a license to buy liquid nitrogen, because of how dangerous it is

 

Liquid nitrogen is less dangerous in nearly every way than boiling water.

"You need a license to buy liquid nitrogen?" "Germanium isn't worth a lot more than silicon?" Where do you get these ideas?

Easiest way to buy LN2 is probably to bring a metal Thermos to a welding-supply shop.  It's not unusually dangerous or difficult to handle.  However, it's not altogether harmless either.  Volumetrically, it will expand by a factor of around 700:1 as it boils off, so you could in principle asphyxiate yourself with a relatively small quantity of liquid in an enclosed space.  I don't know if this has ever actually happened, but it's worth keeping in mind.

And it almost goes without saying that you shouldn't keep it in a tightly-sealed container that can't handle the pressure.  Same as dry ice in that regard.

[Ben321]

You need a license to buy liquid nitrogen, because of how dangerous it is

 

Liquid nitrogen is less dangerous in nearly every way than boiling water.

"You need a license to buy liquid nitrogen?" "Germanium isn't worth a lot more than silicon?" Where do you get these ideas?

Yes, you do need a license. I remember at my high school I went to many years ago, they were going to do a cryogenic demonstration in class, but had to settle on using dry ice for the cold substance being used. This was because when the teacher went to a company that sold LN2 to buy it, the teacher didn't have the proper permit/license to buy and use the substance, so the supplier turned them away (legally the LN2 supplier would not have been permitted to sell it to somebody without the proper permit). They ended up going elsewhere and buying dry ice instead. I'm not sure where you live, but I live in Seattle Washington. It may just be a local law.

[Fraser]

I considered obtaining some Liquid Nitrogen to test my Agema 880 but my local suppliers require the use of an approved Dewar container which in the UK costs around £1000. The idea of transporting the stuff in a car does not appeal either.

On the safety front, i was advised that LN2 is safe in open environs but if a major spill occurred in my closed garage, I would likely expire before escaping    For these reasons I decided it was not worth the effort or risk for a museum piece.

Fraser

[james_s]

You can buy the proper Dewar containers on ebay for around $200.

[Fraser]

Yes true, for a small one that boils off quite quickly. I was going for a 50L tank 

Costs around £1K in the UK.

[james_s]

Jeez, how much does it take to test the thing? I would think a relatively small amount would be sufficient, and opening a window or cracking the door ought to be enough to prevent suffocation if a spill were to occur.

Once you've got LN2 you can make instant ice cream that is supposedly delicious, that's even better than testing a thermal imager

[KE5FX]

I would think we'd have heard a lot of anecdotes about people who asphyxiated themselves with LN2 if it were a serious threat.  If you avoid using it in confined spaces, just as with any volatile chemical, there's really not much that can go wrong.

(Some documents point out that LN2 can also distill LOX from the air and set stuff on fire... but again, has anyone ever heard of that happening?)

[james_s]

It's certainly not something you'd want to carelessly play with, but there are far more dangerous things in most homes than a small flask of LN2.

[Chanc3]

I considered obtaining some Liquid Nitrogen to test my Agema 880 but my local suppliers require the use of an approved Dewar container which in the UK costs around £1000. The idea of transporting the stuff in a car does not appeal either.

On the safety front, i was advised that LN2 is safe in open environs but if a major spill occurred in my closed garage, I would likely expire before escaping    For these reasons I decided it was not worth the effort or risk for a museum piece.

Fraser

Fraser, some of my friends hire in LN for extreme overclocking events - you don't need to buy an approved container then. I'll see where he gets it from.

[Fraser]

Hi Chanc3,

That would be helpful. Thank you It would be nice to fire up the old gal and see if she still runs OK.

With regard to LN2 safety, I agree, it is not a dangerous substance if used sensibly. The dangers rear their ugly heads when an accident occurs, or someone does not understand what they are dealing with. Horror stories of people placing LN2 in sealed (unvented) flask containers thinking it will last longer.... then the inevitable explosion that follows

Fraser

[james_s]

Well there are always gonna be a few idiots out there. Several years ago there was somebody on this side of the pond who decided it would be a good idea to put the glass vessel from a Lava Lite on the stove (hob) and he was killed by the shrapnel. What possessed him to do such a thing I can only guess.

[-jeffB]

Hi Chanc3,

That would be helpful. Thank you It would be nice to fire up the old gal and see if she still runs OK.

With regard to LN2 safety, I agree, it is not a dangerous substance if used sensibly. The dangers rear their ugly heads when an accident occurs, or someone does not understand what they are dealing with. Horror stories of people placing LN2 in sealed (unvented) flask containers thinking it will last longer.... then the inevitable explosion that follows

Fraser
[/quote

Here's one:

http://blogs.sciencemag.org/pipeline/archives/2006/03/08/how_not_to_do_it_liquid_nitrogen_tanks

But I'll still take my chances with a LN2 tank outside my door in preference to a gas/petrol tank. You don't have to look nearly as far to find horror stories about those. You also don't have to do multiple hardware modifications to turn them into something that can explode.

In 7+ years with LN2 and liquid-helium dewars parked outside my office door, the worst mishap I ever encountered was an attack of dust-bunnies being gathered by scattering LN2 droplets from a spill.

[Fraser]

An interesting read......

https://web.archive.org/web/20010507134303/http://www.wpi.edu/News/Releases/19989/nitro.html

LN2 is sadly abused by some who should know better. Ever since I saw it freeze a flowers petals, I have had a healthy respect for it

As stated though, used correctly it is no more dangerous than handling flammable gases or fluids like petrol. In 1996 I watched with horror as a petrol attendant in the middle of Moscow filled my car with petrol whilst smoking a cigarette. Fortunately the fuel air mix must have been wrong as we both lived to fight another day. After that experience I was quite expecting to hear a loud BOOM! one day and see the mushroom cloud rising from this petrol station that was nearby. The petrol tanks were all above ground types too.

Fraser

[bap2703]

Are there any scanning type thermal imagers that do NOT require liquid nitrogen cooling?

Of course there are, basically any temperature sensor.
What creates the cooling requirement is the quantum detection for which the room temperature energy is of the same order than the infrared photon you are trying to detect.
Look for thermopiles or pyroelectric sensors.

[Fraser]

Scanning thermal imaging cameras have been around for a long time and so different detector technology was used over the years. The following are known to me.....

1. LN2 Cooled
2. Argon Gas Cooled using a Venturi and gas expansion
3. Sterling mechanical Cryo cooler
4. Peltier stack cooler

The most user friendly was the Peltier stack cooler as it required no consumables and was not mechanical in nature. The Peltier stack Cooled the detector to -70C and the detector material was Lead Selenide (PbSe)

The Agema 400 series,510 and  870 all used a PbSe Peltier Cooled detector with a scanning image creation system. The Agema 510 was a single axis scanner that contained a 128 pixel linear PbSe array for the vertical pixels. The scanning mirror swung in the horizontal place to create the sweep across the thermal scene.

Note that Peltier TEC's are also used in microbolometer sensors but for a completely different purpose...... to hold the sensor at +32C .... i.e. Not Cooled.

Fraser

[james_s]

So just to follow up, I checked with the Airgas branch that is a few blocks from my house, about 15 miles from Seattle. They do sell LN2, it's delivered from the truck that comes twice a week which may or may not have it on hand that particular time. Their suggestion is to leave your Dewar and they will contact you when it is ready to be picked up. The rep I talked to said no license is required required, you just need an account with them and a proper Dewar flask designed for the purpose. They didn't ask what I wanted the LN2 for and didn't seem to care. Getting an account is as simple as contacting them and providing the contact information they request.

[KE5FX]

So just to follow up, I checked with the Airgas branch that is a few blocks from my house, about 15 miles from Seattle. They do sell LN2, it's delivered from the truck that comes twice a week which may or may not have it on hand that particular time. Their suggestion is to leave your Dewar and they will contact you when it is ready to be picked up. The rep I talked to said no license is required required, you just need an account with them and a proper Dewar flask designed for the purpose. They didn't ask what I wanted the LN2 for and didn't seem to care. Getting an account is as simple as contacting them and providing the contact information they request.

Just get a metal Thermos and bring it to a welding-supply shop.  If they tell you to pound sand, just go to the next one.  Lather, rinse, repeat.  You shouldn't have to visit too many shops before you find one whose employees don't ask too many questions.

Source: this is what I did back in the 1990s to get rid of some warts.  Didn't have to visit any shops beyond the first one.