Another EEV thermal camera - Page 1
Forum section: electronics / testgear

author: artag
author_rank: Super Contributor
timestamp: July 07, 2015, 08:50:26 pm
content: I have an old EEV thermal camera which I think is the same technology as the Argus that Aurora just described. Probably older, certainly less portable.It's an EEV P4200. I haven't been able to get video out of it yet.The lens surface looks somewhat odd - I think there was a coating on it which has blistered.https://drive.google.com/folderview?id=0B8q6sqvuGdFfflBPN1RJakRnTFZaZ0xwUGlhazc1d2xoSkIyTzlPLTdFbnFMaUFDV0x0ME0&usp=sharing

author: Fraser
author_rank: Super Contributor
timestamp: July 07, 2015, 09:17:07 pm
content: @artag,Interesting cameraWith regard to the lens appearance..... Germanium lenses are coated with an Anti-Reflective (AR) coating. This coating increases the Germanium transmission percentage from around 40% to over 85%. The AR coating is fragile and thermal camera lenses must not be polished as that removes the coating, destroying the lens performance.Germanium is a metal that does suffer corrosion in damp environments. Ex Fire Brigade cameras often have corrosion and 'blistering' on the objective lens. This is due to long term exposure to the water from the fire hoses. In this scenario it is hard to keep the lens dry. Moisture gets between the AR coating and the Germanium and the resultant corrosion lifts the AR layer in a blisterAnother form that the Germanium corrosion takes is 'spider lining'. This is where the corrosion forms as fine lines on part of the lens, or even all over its surface.Your lens may be suffering from having been exposed to damp air but this would also lead to corrosion on the cameras screws and chassis parts. In any case, the only cleaning of the lens, that is relatively safe, is the application of IPA on a very soft cloth and you must not press too hard against the lens. Damage due to corrosion is not reversible.Thankfully a lens with minor corrosion will often still function well enough for most applications.Aurora

author: artag
author_rank: Super Contributor
timestamp: July 07, 2015, 10:12:09 pm
content: Thanks !The lens seems to have 'spider lines' as you describe. I think if I clean it with IPA it will just flake off.There doesn't seem to be any corrosion elsewhere, and the inside lens is fine. But the case it's in has rusted catches.What are the chances of getting it to work ? If I find a fault in the support circuitry am I likely to find the tube is worn out ?

author: Fraser
author_rank: Super Contributor
timestamp: July 07, 2015, 10:45:55 pm
content: @artag,I would expect that camera to work fine if you find the fault. The PE Vidicon tube should have held its vacuum and is unlikely to be worn-out.The PE Vidicon can be damaged by leaving it staring at a 'bright' scene for a long period with a fully open iris. The image burns into the thermally sensitive surface. Such burn-in can be temporary or permanent dependant upon severity. EEV ensured that the iris is fully closed when the camera is switched off to prevent damage when left un-powered. Conventional Vidicon tubes suffered from image burn-in as well. It is just a vulnerability of the technology.To get the best from the camera, you need to find whatever is making it non functional and then set the PE Vidicon voltages for correct image aquisition. I can likely help with the tube voltages and required adjustments if needed.The power supply is a prime candidate for failure in these cameras.Does the camera have a chopper wheel ? A non operational chopper wheel prevents the camera seeing a non moving object. Panning the camera from side to side will create a thermal image as the movement creates the required scene change, normally produced by the chopper wheel. To do this test, make sure the chopper wheel is not obscuring the tube face. Also check any iris that is fitted to ensure it works OK.Do nothing with the lens. See how well it works 'as-is'. Thermal cameras do not usually worry about dust on the lens surface anyway. It would be possible to fit another lens but I doubt the cost would be worth it.Aurora

author: artag
author_rank: Super Contributor
timestamp: July 07, 2015, 11:37:38 pm
content: Could well be the power supply. It's a while since I looked at it but there was no video at all - can't remember if there was sync. There is a chopper wheel.