Uniformity issue for Flir TAU cores - Page 1
Forum section: electronics / general

author: Logan
author_rank: Frequent Contributor
timestamp: July 03, 2023, 11:11:36 am
content: I want to finally put this issue on the table, because it happened on more than one core to me and it's annoying.Here's the 4 TAUs for me to compare:1. TAU 324 60Hz v2.4, from Flir FC348-T, 46324009H2. TAU 640 9Hz v2.7.3. TAU 324 9Hz v1, from Flir Scout, 43320019H-SPCAX4. TAU 324 60Hz v2.1.1, from MSA 6000, 46324009H-FPMS45. TAU 324 60Hz v2.1, from MSA 5200HD, 46324013H-FPMS1Their uniformity is 1>3>5>4>2, coincidently (?) the heat they produce is 1<3<5<4<2.The uniformity is actually getting worse as they heat up, so I'm not sure if the good ones will perform bad if they are in higher temperature.The only 640 was so ununiform that I sold it soon after, what a pity.It seems the main cause is the shutter itself is not thermally uniform, because if I block the shutter while doing NUC(and point the sensor to a plain scene), it results in a uniform image, then I put the shutter in front of the sensor by hand, it does show the opposite thermal gradient.Have any of you noticed similar problem, can we fix this by ourselves?Edit: After my treatment to No.4, now their uniformity is 1>4>3>5>2.I only have No.4 now, others are from memory.

author: Fraser
author_rank: Super Contributor
timestamp: July 03, 2023, 12:18:50 pm
content: Whilst I like the TAU cores, they are a compromise between performance and cost. They are basically like the Exx and Autoliv cameras. I am unsure how much non-uniformity they are showing, and under what test conditions, but they were never intended to be “lab grade” cameras. In normal everyday use in a varied delta T scene, there should be no unusual self generated thermal gradients visible. If looking at a thermally flat scene (low Delta T), the core will attempt to pull out thermal details by lowering its thermal span to the minimum available in its particular configuration. Note that some configurations may permit much smaller temperature span settings than others ! The smaller the temperature span, the greater the issues with non uniformity and image noise. A span of 2.0C will usually show up any flat field non-uniformities in a thermal camera system. When you tested your various TAU cores, some may be capable of smaller minimum temperature spans than other for a low Delta T thermal scene. This can make them appear inferior to TAU’s that limit their minimum span to say 8C. Comparing a TAU operating at 2C span with another operating at 8C span is an unfair comparison. This is worth checking in your tests.When the TAU was released, a decent preventative maintenance thermal camera from FLIR cost around £36K. There is a good reason for the high cost of a PM or science use camera…. A lot of effort is put into maintaining excellent flat field uniformity and radiometric measurement accuracy. Sadly the TAU will have had less time and money spent on the same areas of performance. The TAU is a compact and versatile thermal imaging core, but it is not a particularly high performance unit in terms of flat field uniformity and radiometric accuracy.Can the TAU flat field performance be improved ? Possibly, if you are willing to do some modifications. I would suggest disconnection of the internal FFC flag solenoid and installation of an electric FFC shutter on the front of the lens. The flat field calibration then includes the lens assembly in the non-uniformity correction and the shutter is away from the TAU’s internal local heat sources. That said, this is not an ideal solution if radiometric measurement use is intended. This is because the TAU uses its internal ambient temperature sensor to measure the temperature of the air surrounding the internal FFC shutter. An external FFC shutter would likely be at a different temperature and would be susceptible to exterior thermal influences.Fraser

author: Logan
author_rank: Frequent Contributor
timestamp: July 03, 2023, 01:07:48 pm
content: Thank you Fraser.Yes I was testing them under similar conditions and settings. It seems some unit produce more self-heat and become noticeable on the image. Even the best one that looks fine on image, the temperature measurement reading is never stable among different internal heat status.I won't really blame the cameras, as I was testing without lens, I found even a slightly moving hand far from the sensor cause the picture changes significantly, that's hell a lot of sensitivity.Instead of the external shutter, I'm thinking of modifying the internal shutter itself, to make it more uniform across the surface.

author: Fraser
author_rank: Super Contributor
timestamp: July 03, 2023, 01:25:17 pm
content: The TAU FFC shutter flag is actually a decent design so I am surprised that you are seeing this issue of it is pronounced.Operating a TAU without a lens is asking for trouble ! The microbolometer will not have the required illumination and containment for a decent FFC without exterior influences. Thermal energy may leak in around the edges of the FFC flag.Have fun with your experiments thoughFraser

author: Logan
author_rank: Frequent Contributor
timestamp: July 03, 2023, 01:35:23 pm
content: I always set my cores to max gain limit, because the default looks too flat.Thank you again!

author: Fraser
author_rank: Super Contributor
timestamp: July 03, 2023, 01:50:02 pm
content: If a scene appears too flat, it is normal to change from Linear to Histogram equalisation mode, rather than max out the gain.

author: Logan
author_rank: Frequent Contributor
timestamp: July 03, 2023, 02:11:33 pm
content: Quote from: Fraser on July 03, 2023, 01:50:02 pmI'm already using Histogram equalisation mode...

author: angelortega
author_rank: Contributor
timestamp: July 03, 2023, 03:16:14 pm
content: I had my tau2 640x480 camera shutter fail.I put a post-it on the front of the lens and wow.The image looks great,I think its the even temperature and texture Of the paper. Holding the entire book in front of lens helps to keep it flat,do not use a single sheet,temperature from your hands will bleed through Try it. See if the image is more uniformed

author: angelortega
author_rank: Contributor
timestamp: July 03, 2023, 03:20:27 pm
content: Sorry forgot set flat field correction to external first

author: Logan
author_rank: Frequent Contributor
timestamp: July 04, 2023, 12:59:20 pm
content: I found a "solution".I cut a piece of electrical tape that has a larger surface than the FFC flag, then stick it to the flag, on the side that face the sensor.I don't know if it's the bigger area, or the material, but this does improve the uniformity, not completely though, I think I need to tweak it more.Quote from: angelortega on July 03, 2023, 03:16:14 pmThank you, but won't it drift overtime? You will have to do that periodically, right?

author: angelortega
author_rank: Contributor
timestamp: July 04, 2023, 05:05:30 pm
content: to start the camera with the shutter that failed was removed from a flir marine ptz the number is 46640001x with a big E next to it. Your right it will drift, but i put the camera outside my window for 4 hours on a very Hot day it show a small amount of drift,but what I liked is the fact that the camera does not go through the larger scene changes like when a hotter object moves thru the field of view, hell if I was a single little sensor beening asked to always change my temperature every few seconds just because the camera wants to show who's the hottest of all, it's nowonder there's a lot of noise and unevenis in the image. My camera does change in small amounts only. I like using post-it it's more like a satin finish does not reflect a lot of light. hold the tape and post-it near a light if you see reflected light,the hot sensor mite see it's reflectiontry this take picture of hot objects at home with the tape shutter and then with the post-it of the same objects see if there is a deference.

author: Logan
author_rank: Frequent Contributor
timestamp: August 05, 2023, 05:17:08 am
content: I found another thing affecting the shutter performance.It's much better to run the TAU core inside a enclosure instead of open air.This will reduce the temperature difference across TAU's metal case and internal, which the shutter is very close to.

author: Bill W
author_rank: Super Contributor
timestamp: August 05, 2023, 10:47:38 am
content: There are other factors of nonuniformity to deal with........As well as whatever happens on the flat field, if the core decides that the sensor is at a different temperature, it will apply the wrong gain per pixel by temperature.Most likely to result in column effects, worse on flat scenes far removed from the shutter temperature (as the flat field will have tried to fix it).A significant difference in lens metalwork temperature from the shutter will result in a 'porthole' / hot centre. This is energy from 'beyond the shutter' in most cases so is going to get images. You do not get this with 'shutter in front of lens', and much depends on how much lens metalwork can be imaged. Careful baffling may help.A similar effect can happen with lens narcissus (rear element reflecting sensor heat back in).No shutter is ideal e=1, but some can get quite bad, effectively reflecting the hot sensor back into the sensor and getting that embedded in the flat field.

author: johnelot
author_rank: Contributor
timestamp: August 13, 2023, 07:00:57 am
content: when i wa making a thermal monocular i started with a plastic housing but soon got problems from the core heating - when i switched to aluminium (imade sure it was attached to the core frame )i had no problems - not a flir core but might be relevant

author: Logan
author_rank: Frequent Contributor
timestamp: August 13, 2023, 03:06:03 pm
content: Quote from: johnelot on August 13, 2023, 07:00:57 amThanks. I have the opposite experience. The core would perform better with bad heat dissipation, because it make the shutter to have lower delta T across the surface.