The perils of buying cooled thermal cameras
As some readers will already know, I am a user and collector of thermal camera technology.
At last count I own 39 thermal cameras of varying technologies and ages.
My favourite cameras are those from the FLIR PM industrial series and some of the NEC AVIO models.
I already own one cooled camera, the FLIR Scientific SC3000 that uses a Stirling cooled Quantum Well imaging array. When I say ‘cooled’, I do not mean temperature stabilised, that is very different. A cooled camera uses either Liquid Nitrogen or a closed circuit Stirling Cooler that produces temperatures approaching -200C. At one point in time there were cooled scanning cameras that used Peltier cooler stacks to cool a single pixel detector to -70C, but these are long obsolete technology.
Cooled thermal cameras pre-date uncooled Microbolometers, but are still made and used for demanding situations where very low noise images are required without all manner of software manipulation algorithms that could corrupt the data. Such cooled cameras are very expensive to purchase and run. The Stirling Cooler alone costs around $15000 to the OEM and RICOR are a major player in that market.
(
http://www.ricor.com/innovation-technology/stirling-cooling-technology/ )
Why are they expensive to run ? Well they are a very high performance machine that contains pistons, seals and a gas fill of Helium that is at enormous pressure. Helium molecules can escape past seals and even through the thick metal shell of the cooler. This means that over time the Helium Fill pressure drops as Helium gas escapes from its captivity within the cooler. Mechanical wear in the precision components also leads to a drop in performance. It is not unusual for a Stirling Cooler from the late 1990’s to require a complete rebuild every 2000 operating hours. Stirling Coolers are usually rebuilt when they need a new fill of Helium. This used to cost me around £5000 when FLIR offered the service. It is most definitely not an amateur DIY proposition as ultra-pure(UP) Helium at pressures in excess of 200psi is used. So every 2000 hours or few years (depending upon the Helium leakage rate, you have to spend around $7500 on the camera.
When looking to buy a thermal camera it is wise to investigate the technology that resides within, or else you may make a costly mistake. Many older thermal cameras are advertised on eBay as ‘unable to test’ or ‘sold as seen’. Be wary of such cameras and investigate why they are described as such. In many cases it is because they require liquid nitrogen to be poured into their internal Dewar (vacuum flask cooling chamber). Liquid Nitrogen is a very inconvenient consumable to need for your cameras use. Without it, the camera is a paperweight. If the camera is equipped with a Stirling Cooler , there is the distinct possibility that the cameras cooler is either faulty or has lost its Helium Gas fill, rendering it incapable of cooling the sensor array. Again, this results in the camera becoming a paperweight. You could have the cooler rebuilt, but I know of no cheap way to achieve this and such professional services still cost many thousands of Dollars, and the providers of such services are few and far between (usually return to OEM only), Many OEM’s no longer support such obsolete products.
If a Stirling cooled thermal camera is found in working condition, be aware that it is a bit like an unstoppable egg timer, with its coolers life decreasing every day as the Helium escapes. Some coolers continue to work many years beyond their predicted life, whilst others fail more quickly. Even NASA have this trouble with their space rated Stirling coolers used for vehicle instrumentation cooling. Helium leakage can vary from one cooler to the next and some will remain working after 15 years, whilst others have lost enough Helium after 5 years to cause failure. Cameras that were used in labs may have received a rebuilt cooler several times during their life. If possible, establish when the last cooler was fitted. That is not the last calibration data so do not be confused into thinking that calibration involves a new cooler or re-gas.
Some types of cooled camera have very hard lives. Namely those used in the military and CCTV applications. The coolers were often running for many hours and suffered mechanical failure before the Helium Fill was lost (bearing failure is a common issue in the Stirling cooler mechanics). With the introduction of new, and more reliable, uncooled TIC technology, many such cameras were consigned to the ‘Stores shelf’ or disposal basket. These cameras are unlikely to be operational and should be avoided.
There is a saying in the UK…… “do as I say, and not as I do”
I want to tell you a story.........are you sitting comfortably ?
I recently saw a very nice condition Inframetrics PM280E cooler thermal camera for sale on ebay for a starting price of £600. I was interested in this camera as it is a mid-wave unit and this example was complete with the very expensive High Temperature filter. This may be attached to provide use up to 1500C. If I am truly honest, I have never liked the Inframetics PM series (very different to the FLIR PM Series). They did not seem as neatly designed in some ways. By the way PM prefixes usually just mean a series for ‘Preventative Maintenance’ . Both Inframetrics and FLIR had their own PM series camera and things got more confusing when FLIR absorbed Inframetrics into its ranks. But that’s another story.
Anyway, back to the Camera in question…..
I contacted the seller to establish some facts about the camera. It was apparently in excellent condition with all accessories and the important optional ‘HT’ filter. It was said to be in working order and the cooler was working OK. I asked if the Maintenance warning was flashing in the display and was told it was not. This is important as the warning indicates that the camera needs a service. If this has been ignored it does not bode well for the coolers maintenance. I satisfied myself that the camera was operational and advised the seller about the perils of buying a Stirling cooled camera.
We agreed that if the camera did not sell on eBay, we would discuss a mutually acceptable price for it. The camera did not sell and I spoke with the seller again. He understood the risk of me buying the camera and asked for an offer. I offered £300 and he accepted. A great deal some might think (me included).
The camera arrived and was in its posh flight case complete with all accessories and three batteries. I powered the camera via its mains adapter and the colour viewfinder burst into life. It immediately indicated “Maintenance suggested” at the bottom of the screen
……. I got that awful sinking feeling that you get when you think you have been conned. I left the camera running to complete its cool-down cycle.
A camera with a healthy cooler will take between 5 and 7 minutes for the cooler to get to operating temperature at the ‘cold finger’ (the attachment point to the sensor array). As the coolers Helium Fill diminishes, with associated lowering of gas pressure, the cooler takes longer to reach the operating temperature. A camera that takes 15 minutes, or more, to complete the cooling cycle needs a Stirling cooler service. My PM280E was still trying to reach operating temperature after 40 minutes…..there is insufficient Helium left in the cooler for it to do its job. It valiantly tried but failed to ever meet its target temperature. In STAR TREK speak….”Its dead Jim”
OH cr*p was my response to this discovery. I had a lovely condition cooled thermal camera that promised so much but was incapable of cooling its sensor array. B*gg*r £300 wasted. It was a cash 'sold as seen' deal so there will be no refund coming my way any time soon.
I advised the seller of the situation but, as expected, no response. His view is likely that it worked to the best of his knowledge (which was minimal on thermal cameras). My huge mistake was not getting him to email me pictures of the camera actually displaying a thermal image. I was not on the ball this time (others things on my mind), too trusting, and I have got myself burnt. You live and learn. I am telling this rather embarrassing tale in the hope that it prevents others making the same mistake.
The bottom line is...... I recommend you do not buy uncooled thermal cameras unless you know an awful lot about a cooled cameras history and that it has a newish cooler fitted. Without such knowledge you risk buying a turkey, like I have just done.
Remember..... if a cooled cameras Stirling cooler fails……. It’s is just a posh paper weight !
I believe in KARMA and in my world I will not waste precious time chasing the seller or worrying about my loss. It could have been far worse as I have spent more than a £1000 on cameras in the past. This is my first mistake in 39 TIC purchases, so I have not done badly. I bought a beautiful condition FLIR PM575 for only £150 a few months ago so such bargains offset this loss.
What of the PM280E ?
Its fate is yet to be decided. I may sell it as spares, or break it up as a parts donor. It may just sit in my collection as a reminder of getting greedy and its potential consequences. That alone is probably worth £300 to me.
An interesting side note for thermal camera fans….. the 16 Degree lens on the PM280E is not made with Germanium lenses. It uses two large ZnSe or ZnS lens elements, the front lens element having what look to be Fresnel rings on it. I knew some military lenses contained ZnSe or ZnS lens elements internally but this is the only camera that I have seen that uses them for the first two elements. ZnSe and ZnS both have excellent bandwidths and transmission figures. There is a conventional Germanium lens in the cameras bayonet mount, and this forms part of the lens system that may have other interchangeable lenses placed in front of it, much like the AGEMA 880 lens system. Part of it is in the lens barrels and part is fixed in the camera body. Modern thermal cameras with interchangeable lenses tend to change out the whole lens assembly right up to the microbolometer as they use smaller or cheaper lenses in their construction. Germanium is so expensive that OEM's tried to reduce its quantity in the optional lens barrels as much as was possible.
Be careful out there
Aurora
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