Random thought---When will uncooled/TEC cooled WMIR cameras present? - Page 1
Forum section: electronics / general

author: sam1275
author_rank: Frequent Contributor
timestamp: October 08, 2016, 09:04:41 pm
content: Hi everyone, this is just a free thought of mine.As you know, Mid-wave Infrared cameras offer better spectral resolution, longer detection range, and lower NETD than LWIR ones. But until today, all MWIR cameras still need deep cooling system for the sensor, maybe down to about 77 kelvin I think, such design makes MWIR cameras bigger, power hungry, expensive, slow to start, and need regular maintenance which is not cheap and cannot be done at home.I remember FLIR told me in a email that MWIR cameras must be about a thousand times higher sensitive than LWIR ones, because the thermal radiation is a lot less in the MWIR range, and sensor must be cooled because otherwise it will drown in it's own noise and cannot tell those weak signals.However I still think it's not a physical limit that MWIR cameras must be cooled, it may just need time for scientists to make a high S/N ratio sensor?For those who don't know, there are basically two type of sensors, one is microbolometer which measures the temperature change of itself, to tell what happens in the scene, which is usually seen in LWIR cameras. another is working by sense photon striking on it, more like a visible light camera, usually used in a MWIR camera, this type react faster than microbolometer.So what you guys think? Will there be a uncooled MWIR camera in the future? When? Personally I think yes, in 30 years...Or another approach, why not make a TEC cooled version? I've heard TECs can also be very cold in a serial design, although it will use more power than stirling cooler, it will barely need a complex maintenance, and they should already able to make one by today's technology.Thank you for reading and feel free to talk

author: Fraser
author_rank: Super Contributor
timestamp: October 10, 2016, 06:43:18 pm
content: My comment on the TEC cooler idea.TEC's have already been used in thermal cameras for cooling rather than the more common temperature stabilisation role. The Agenda Thermovision 400 camera used a Peltier TEC to take the detector down to minus 70C.TEC coolers are very power hungry and so less suited to portable battery powered cameras. The Agema 400 was around the size of a circa 1990's outside broadcast camera.You can miniaturise camera electronics but sadly the physics of the TEC works against you. A Peltier stack is used in the Thermovision 400. It is not just a case of putting a load of Peltier stages on top of each other. Each successive stage must be larger in size than its predecessor as it has to cope with not only its own heat output, but also that of the previous stage. It ends up like a pyramid with the detector at the tip. The Peltier stack cannot achieve the required temperature differential across itself in free air. It has to sit in a vacuum Dewar that acts like a vacuum flask. The vacuum flask greatly decreases the thermal load on the TEC but also increases cost and solution complexity.After all this effort, the TEC Peltier stack achieves only -70,C from an Ambient of say 30C. A differential of 100C. A Sterling Cooler takes its cold finger down to -196C. Such low temperatures are needed for high performance low noise cooled cameras.So how did the Thermovision manage with just -70C ?It used an exotic detector material. I forget which one, but it can operate at an acceptable level when cooled to just -70C. IIRC it is a SWIR detector.The Thermovision 400 series did not continue in FLIR"s offerings and was replaced with Sterling cooled cameras like the PM550 and the Microbolometer equipped uncooled PM570 etc.Fraser

author: Bill W
author_rank: Super Contributor
timestamp: October 10, 2016, 08:22:08 pm
content: A couple of other points going against peltier stacks for thermal cameras:Thermal sensors tend to be quite big, and with a fair amount of on-chip electronics. You get stacked Peltiers for visible CCD which are smaller and at the typical -70°C there is a worthwhile noise reduction.Peltiers are a pain for outgassing, and thermal sensors need a good vacuum .Bill

author: Fraser
author_rank: Super Contributor
timestamp: October 10, 2016, 09:00:16 pm
content: A small correction on my part. The AGEMA camera was the Thermovision 450 and 470 models, part of the 400 series.Picture and brochure images attached.Fraser

author: sam1275
author_rank: Frequent Contributor
timestamp: October 11, 2016, 06:20:08 am
content: Quote from: Fraser on October 10, 2016, 06:43:18 pmThank you very much. So TEC's best ability is -70C, it 's worse than I thought, it's definitely cannot compete with a mechanic cooler.

author: sam1275
author_rank: Frequent Contributor
timestamp: October 11, 2016, 06:24:50 am
content: Quote from: Bill W on October 10, 2016, 08:22:08 pmThank you for replying. But why must put the TEC inside the sensor package? Can't we just cool the sensor like cooling a CPU? (The cooler is not inside the CPU, but touch with a thermal conductive material on the CPU)

author: Bill W
author_rank: Super Contributor
timestamp: October 11, 2016, 12:57:58 pm
content: Several things mean that peltier in package is better:More efficient without the air / convection leakageNo condensation problems (or need for a second dry sealed volume if you go that way instead)Short response time. In contrast to the CPU example, the thermal sensor would normally be maintained at a set temperature or compensated for that. So peltier - in - package is quite good for control loop stability.If the wide-band sensor is OK simply being cold (and the wideband type may well be) then that becomes a more valid option. In CCD's all that happens is dark current / noise falls off with cooling, in a thermal sensor your whole calibration changes.Bill

author: sam1275
author_rank: Frequent Contributor
timestamp: October 11, 2016, 01:52:16 pm
content: Quote from: Bill W on October 11, 2016, 12:57:58 pmThank you very much, well explained

author: Fraser
author_rank: Super Contributor
timestamp: October 11, 2016, 02:28:57 pm
content: Sam,That is the nice thing abut this Thermal Camera Sub forum, there are many friendly people here willing to share both theory and practical experience.Bill is a good example of such. He has forgotten more than I ever knew about thermal imaging camera designI know of no other forum on the internet that has the depth of thermal camera knowledge available to its membership. Many manufacturers employees are restricted in what they are permitted to say in public. This is your best chance of getting straight answers to questionsIf you want to know a bit more about the cameras that Bill has been involved with, take a look at his web page and associated forum.www.fire-tics.co.ukA top notch chap who is ever helpfulFraser

author: sam1275
author_rank: Frequent Contributor
timestamp: October 11, 2016, 04:49:47 pm
content: Quote from: Fraser on October 11, 2016, 02:28:57 pmThank you, one night I searched and read most of your postsand I looked at that site you mentioned.