Vintage Inframetrics Model 740 (cooling problem) - Page 1
Forum section: electronics / general

author: pamperchu
author_rank: Contributor
timestamp: May 22, 2019, 02:34:37 pm
content: I have a Inframetrics Model 740 that doesn't cool down at all and shows a white/blank image even after 30min running. my guess right now is that the helium has leaked out of the cooling pump over the past 30 years....I found what looks like a fill valve inside the scanner and wanted to know how refilling/servicing would have been done. all the documents I could find so far tell you to call the manufacture or send it in for repair.A service manual would be great if anyone knows where to find one for this type of system.

author: Spirit532
author_rank: Frequent Contributor
timestamp: May 22, 2019, 05:45:45 pm
content: Find the pressure rating, hook it up to a high vacuum system, pump it down to 1*10^-9 — 1*10^-10 torr, refill with pure(not balloon grade!) helium, reseal.

author: Fraser
author_rank: Super Contributor
timestamp: May 22, 2019, 08:59:08 pm
content: Cooler is filled with Ultra High Purity Helium (UHP Helium) Anything lower quality will not work well. The pressure is 200psi. The fill port seal is special soft metal and not reusable. A bespoke fill port nozzle is required.The filling process does not usually vac down the cooler and a fill then vent cycling process is used to flush the cooler Helium chamber.In most cases the work to fill a Stirling Cooler exceeds the cameras value. The coolers can also suffer mechanical wear and failure.Fraser

author: pamperchu
author_rank: Contributor
timestamp: May 22, 2019, 09:00:04 pm
content: what purity of helium is required? will regular grade He damage the system in any way or just not work well?I have the tools to do this, not as complex as I thought it might be. thanks for the help

author: Fraser
author_rank: Super Contributor
timestamp: May 22, 2019, 09:05:59 pm
content: UHP Helium only. Any impurities freeze and can destroy the cooler through piston seizing. All gases in the cooler have to remain a gas at -196 Celcius.The fill port nozzle is externally threaded and incorporates a tool to install the metal seal gasket and its seal screw.Fraser

author: pamperchu
author_rank: Contributor
timestamp: May 22, 2019, 09:08:44 pm
content: yah the valve does have a plastic cap covering it, didn't see clearly what was underneath yet.I don't really care about the cost of repair, this is what i do for fun.

author: Fraser
author_rank: Super Contributor
timestamp: May 22, 2019, 09:10:38 pm
content: The fill port metal seal gasket is made from Indium and can be a disk or ball that is crushed by the seal screw.Fraser

author: pamperchu
author_rank: Contributor
timestamp: May 23, 2019, 03:58:46 pm
content: thank you for all the help given, here's 2 videos ive posted so far on the project.

author: Spirit532
author_rank: Frequent Contributor
timestamp: May 23, 2019, 05:43:22 pm
content: A fridge vacuum pump won't work. You need a rotary vane pump for roughing, and an oil diffusion pumpwith bafflesand cold trapto get down to a vacuum that is low enough to get rid of the stuff that's leaked in over the years.Quote from: Fraser on May 22, 2019, 08:59:08 pmThat would work, but you'd need an absurd amount of helium to flush out everything that got in there over the years, not to mention an unprofessional filling setup willdefinitelylet tons of air and moisture in.A vacuum setup will ensure that there's nothing in there that can freeze and destroy it.

author: Fraser
author_rank: Super Contributor
timestamp: May 23, 2019, 06:02:06 pm
content: Spririt532,Yes I agree and UHP Helium is not cheap ! My comment was as a result of hearing how new coolers are filled. Used coolers can also have all manner of issues and some never work properly until rebuilt.This is why I love Cooled cameras, but dislike risking money on them. They can be expensive paperweights and I have two of them that need cooler refills or rebuilds. They are Inframetrics PM280’s and FLIR quoted £7K to £9K per camera to have the coolers rebuilt/replaced. That price included calibration but not postage to and from the USA. I was very nervous about spending £930 on the FLIR S4000 for this reason. I had no ‘hours run’ reading from the seller so it was a very real risk. Thankfully the SC4000 is relatively modern and contains a linear Stirling cooler with a good reputation for long life and reliabilityAs I have said previously on the subject, with the SC4000 I got very luckyFraser

author: Fraser
author_rank: Super Contributor
timestamp: May 23, 2019, 09:13:55 pm
content: OK just watched some of the second video and need to provide some comment as there appears to be confusion regarding the cooler location.The Stirling cooler is the gold coloured unit mounted on the rear of the thermal sensor glass dewar. It is a totally self contained unit comprising the cooler motor, dual ‘pistons’, vacuum dewar and thermal sensor. The Helium fill port is just a threaded hole with what will appear to be a socket head grub screw at the bottom of it. I can see it clearly in your video sticking out of the coolers housing. Be certain the cooler is the fault before opening that port as there is no going back once you do. Cameras can take as long as 20 minutes to teach 77K when some Helium has been lost but the cooler still has enough to reach and maintain the target temperature. The coolers motor speed reduces audibly when the target temperature is reached. Helium is a very efficient gas for a cooler and greatly improves the coolers performance. It also has the essential low temperature capability required for a cryo cooler. The Stirling mechanical cooler is a somewhat different beast to your average refrigerator or freezer compressor based system. Losses must be kept to a minimum in order to reach 77K. Hence the glass vacuum dewar around the ‘cold finger’ and thermal sensor. Cooling capability is minute. These things draw relatively little power and, unlike a Peltier cooler, do not generate a lot of heat when cooling the cold finger. Despite your hopes, I regret to advise that recharging a Stirling mechanical cooler is anything but simple, even for experienced refrigeration techs. I have spoken to such techs who had the correct UHP Helium, correct regulators, correct hoses and correct adapter to attach to the coolers fill port. They had detailed OEM recharging instructions and followed them to the letter. The recharging exercise failed on three different Stirling Coolers and all three ended up being professionally recharged by the coolers OEM at great expense. Precision engineering is an essential part of the coolers design and sadly even low hours coolers can fail and not be recoverable without a rebuild by the OEM. I hope you prove me wrong with yours as it has very low hours and I would love to see someone succeed in recharging a Stirling cooler from a thermal camera.The larger black object you thought was the Stirling cooler is in fact the module that contains the scanning mirrors and their galvanometer drive systems. The mirrors operate in a vacuum to remove air resistance from their movement and so increase efficiency. The galvanometers are run in a resonance mode of operation. The port with the blue cap is the vacuum port for that assembly.You can download the user manual for your camera from the FLIR manual archive and I believe that contains a picture of the various parts of your camera. I will see if I can find a link for you.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: May 23, 2019, 09:22:23 pm
content: 740 User manualhttps://support.flir.com/DocDownload/Assets/dl/07470-000$b.pdfFLIR archive Inframetrics manuals......https://flir.custhelp.com/app/account/fl_downloadsNo account needed for user manual access and downloads.The 700 series manual is a useful reference as well and provides insight into the camera design. Inframetrics Patents likely offer further insights.https://support.flir.com/DocDownload/Assets/dl/t559096$a.pdfFraser

author: Spirit532
author_rank: Frequent Contributor
timestamp: May 24, 2019, 05:30:45 am
content: One way to try "restoring" the system's operating performance would be to "top up" the helium with regular(non-UHP) by cracking the fill port slightly(maybe 1/100th of a turn, just enough to let a few micrograms of helium in), and then screwing on a high pressure(500psi or so) helium input, then letting it sit for a week. This might leak enough heliumintothe system to keep it running, while keeping all the contaminants out(due to the tiny hole).This is a neat trick I've seen used in restoring vintage He-Ne lasers - though that involves "bathing" the entire tube in a tank of atmospheric pressure helium for several weeks. The helium just diffuses through the glass.

author: Cat
author_rank: Regular Contributor
timestamp: May 24, 2019, 08:32:03 am
content: Quote from: Fraser on May 23, 2019, 09:13:55 pmJust a thought: Is it maybe possible to reverse this and get more more cooling-power by driving it "harder"?The cooling power should be related to the input power and RPM of the motor. I don't know what kind of motor the Inframetrics uses, the only stirling I could get my hands on needed 3ph 28V 400 Hz (probably an induction motor). To decrease the speed the voltage could be lowered to increase the slip. To get more power the frequency (and maybe voltage) needs to get raised.

author: Fraser
author_rank: Super Contributor
timestamp: May 24, 2019, 08:42:01 am
content: Spirit532,That is a really interesting ideaI had considered connecting up a cylinder of balloon Helium and trying to ‘top-up’ my PM280 camera coolers as they will actually achieve operating temperature if left in the fridge to cool the whole camera to +5C. They are just suffering from age related loss of Helium fill rather than cooler failure or total loss of Helium.Balloon Helium is so common and inexpensive that it is surely worth a try before scrapping a camera. There is nothing to lose in such a case. The only issues I am aware of are that the modern disposable Balloon gas cylinders usually have a 200psi fill pressure but sadly incorporate a pressure reducer in the output valve (that cannot be removed) and also there is a move to fill such cylinders with a 80/20 mix of Helium and air. The Helium/Air mix is used for two reasons. It saves Helium which is a non renewable gas and it addresses the common use of Helium gas for suicide. The 20% air content is a serious level of contamination that would not be good for a precision Stirling coolers health.I checked with a few disposable and rental Helium cylinder suppliers. The Rental cylinders appear to offer Helium that is not mixed with air but it is also not guaranteed to be any recognised level of purity. The storage reservoir used to fill such cylinders is filled with many sources of Helium, including that from partially used rental cylinders. It can contain relatively high levels of impurities.Cylinder rental companies like BOC can provide Helium of stated minimum purity at reasonable cost. UHP Helium is commonly used in science as a reference gas and is very expensive due to the processing of the gas before the cylinder is filled. It is very pure to avoid reference contamination issues. Slightly less ‘guaranteed pure’ Helium would be a better option than common, often adulterated, balloon gas.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: May 24, 2019, 09:01:00 am
content: Cat,I honestly do not know. The cooler runs at a fairly high RPM when in ‘cool down’ mode but it is a heat pump and it is my understanding that the speed of the pump effects the rate at which heat is removed from the cold finger. I am not sure whether the speed of the motor influences the minimum achievable temperature. Maybe so in a relatively high thermal loss system but the cold finger sits in a vacuum dewar to minimise losses and improve cooling efficiency of the Stirling cooler. The cooler motor speed is reduced once the required operating temperature is reached as the cold finger becomes a thermal mass that just needs its temperature maintenance within the excellent insulation of the Dewar. There is also conducted heat involved but the cooling ‘effort’ is not great so the motor can drop to its ‘maintain’ cooling speed.The first signs of a cooler that is in trouble due to Helium fill leakage is the time it takes to cool down to 77K. The common cooling time is 5 to 10 Minutes. 15 minutes is not unknown though. Anything longer than that indicates the cooler is struggling. If the cooler gets to 77K but cannot drop into ‘maintain’ mode and stay there, it is another sign of trouble either with the Helium fill or the dewar vacuum. A camera that reaches 77K but then cannot maintain it for long is commonly suffering from Helium fill leakage as when the camera and cooler is cold the cooler achieves 77K, but the cooler and camera will warm up due to normal sources of heat within them. The cooler then cannot provide the ambient to 77K thermal differential required and so the cold finger temperature rises above 77K. A simple test for a camera that is not reaching 77K to produce an image is to place it in the fridge to cool the whole camera to +5C. Then power the camera and see if it can reach 77K. The reduction in ambient temperature is sometimes enough to achieve 77K in a camera that is still close to achieving operating temperature. Sadly the camera then warms up due to internal heating and 77K cannot be maintained. I even considered fitting a Peltier cooler to one of the coolers in my PM280’s as it works when cooled to 5C, but not when in an ambient above 15C. That 10C differential makes all the difference in this case.I placed the PM280 in the freezer to see what cooling the unit to -18C would do..... the camera electronics did not like it, neither did the firmware when it saw a chassis temperature that low ! It did work but there was all manner of weird behaviour from the cameras controls plus condensation became an issue.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: May 24, 2019, 11:02:07 am
content: I came up with a design for the fill port adapter and presented it to someone who knew about such things. It was a feasible solution for attaching to the fill port.The design was for an externally threaded brass tube with a side port for connection to the Helium cylinder hoses and regulator. Down the middle of the threaded brass tube there is a screwdriver to loosen and tighten the sealing screw. The screwdriver shaft passes through a suitable seal that is built into a brass ‘end cap’. A flange around the screwdriver shaft is positioned in a yoke that prevents the shaft becoming a 200psi propelled projectile ! The externally threaded brass adapter tube has a flange and seal that presses up against the side of the cooler to form a gas seal.In use the adapter would be connected loosely (deliberate leakage) to the coolers fill port and the Helium hose connected to it. The Helium regulator would be set to a low pressure and Helium released into the hoses and adapter to flush out the air. During the Helium flush phase the adapter would be tightened to seal against the side of the coolers case. The regulator pressure would be slowly increased to 200psi whilst checking for leaks or other issues with soapy water. Once set at 200psi, the screwdriver would be engaged in the coolers sealing screw and turned to break the gas seal. The Helium at 200psi should force its way into the cooler. After a period of ‘soak’ the screwdriver would be used to tighten the sealing screw onto the Indium sealing gasket. The Helium gas is turned off and the pressure in the hoses released slowly by unscrewing the adapter from the cooler or loosening the hose connection at the Helium regulator.Now the bad news. The Indium seal can take different forms and is crushed into the fill port seat. It is supposed to be a single use seal. It cannot be removed without releasing all of the Helium from the cooler. We are looking to ‘top up’ the Helium though. The Indium seal may be a crushed sphere design that will not permit the external Helium at 200psi entering the cooler tat is at less than 200psi internal pressure. Even if Helium is forced into the cooler, the Indium seal may fail if reused. All risks, but well worth a try.If all else fails, the cooler can be vented, a new Indium seal made and the Helium fill comp,Evelyn replaced using a fill and vent process that eventually pushes the air out of the coolers casing. The quality of the fill/vent process and the Helium gas will then dictate success or failure.Before attempting any of the above, remember we are dealing with relatively high pressure gas from the Helium cylinder and it’s regulator. Such pressure can cause parts to become projectiles and if parts rupture under the pressure, there is the potential for shrapnel and serious injury. I recommend that face protection and other safety measures are employed during the process.Fraser

author: Spirit532
author_rank: Frequent Contributor
timestamp: May 24, 2019, 05:50:53 pm
content: Quote from: Fraser on May 24, 2019, 11:02:07 amYou don't want to break the seal. 200psi is still far too low. If you want to "top up", you need the pressure to be equal or higher than that in the cooler, otherwise you'll just leak UHP helium back into the cylinder.The idea here is to damage the seal ever so slightly, so that a few atoms can get through bit by bit, and leave that side sitting at an extreme(100psi+ above the internal) pressure over a period of many days to let it seep in.

author: pamperchu
author_rank: Contributor
timestamp: June 01, 2019, 12:37:10 am
content: thank you everyone for all your help. I will put it all back together and let it run as long as it needs to [30-60min] and see if i was just being impatient before attempting further repairs...I had another idea that might be a fun attempt at repairing/modding the device if i cannot find the correct tools to refill the helium [if that is the problem]so my idea was to take a thermal spot heat gun, the kind that are used for spot temp measurements, and use the CCD from one along with the electronics and mechanics from the original vintage camera, keeping the mechanical scanning xy optic block and main A/D imaging electronics. if I have to make it a slow scan thermal camera I could, but actual max clocking of what I have might be able to go higher with proper cooling and some changes in scan speed.right now its just an idea with spare parts i have sitting around. I would like to try and make the original one work first, but if not i can always get another "working" vintage cooled one off ebay.

author: Spirit532
author_rank: Frequent Contributor
timestamp: June 01, 2019, 12:43:08 am
content: That'll never work.They're just far too noisy.You can build a very slow scan system, but it'll take minutes per image and it'll be a very low resolution, noisy image. No point in doing that over buying a cheap dongle.