Uni-T 165A, weird calibration issue - Page 1
Forum section: electronics / general

author: Quaxo76
author_rank: Newbie
timestamp: February 26, 2023, 10:21:42 pm
content: Hello,I have a Unit-T 165A thermal imager that behaves in a weird way.I bought it new from China. It was brand new, with no signs of previous use at all. Build quality seems good, quite heavy and solid, long lasting battery, and rather good image quality for the price range (actual 160x120 resolution).The problem is with the temperature readout. I mean, if I just look at the images, they're all right. Very sharp details, no dead pixels, good focus, etc. But the numeric readings act weird. Basically, around 25°C they're sort of right. But anything colder or warmer than that, gets a progressively "exaggerated" reading. I.e. if I measure my room's walls, they're at say 15°C near windows, but the meter reads 0 to 5 degrees. Something at 0 degrees might read -15, and something at 50 might read 80 or 100. I don't have the exact numbers, but you get the point. It gets wildly inaccurate, the more inaccurate the farther it is from 25°C.I've tried switching units, and playing with emissivity along the whole range, and the issue is still present.I've disassembled the unit (after realising that the seller won't replace it, and it's impossible to contact someone at a technical department at Uni-T). I was hoping for some mis-calibrated trimmers or something, but apparently everything is done in software, as there is nothing to tweak at all.I've looked for a way to upgrade the firmware, but I couldn't find anything. The current firmware version is V2.1.I can provide example pictures if needed.Has anyone ever seen a similar behavior? Is there anything I can do to try to fix this? As it is, I can use the imager for nice qualitative measurements, but no quantitative work at all...Thank youCristian

author: Bill W
author_rank: Super Contributor
timestamp: February 27, 2023, 12:55:02 pm
content: The fact that it is correct around ambient, means almost everything is working. Flag, flag temperature etc.You are overreading, so the detector has not lost sensitivity since calbration.Now say look at 60°C (say cup of hot coffee).As you change emissivity does the reading change ? It should.If not it is a software bug (maybe user inflicted) that is not letting you set emissivityFor most purposes emissivity = 1.0 is safest. The camera cannot really know the temperature of any reflections so eliminates those errors.It could simply be a bad factory calibration (forgot to turn on one of the charts) and those rejects are simply being dumped by the usual 'we not allow return' fraudsters in China. The camera builders are often not the same people building and calibrating the cores.

author: Quaxo76
author_rank: Newbie
timestamp: February 27, 2023, 10:13:14 pm
content: Quote from: Bill W on February 27, 2023, 12:55:02 pmYes, changing the emissivity the reading changes, but even at the extremes, not enough to give a good reading. And for my tests I chose object that don't have a lot of reflectivity. For example, I just took a reading of the white wall in my room. The 165A reads -3°C, but the ambient temperature is 20C (confirmed by a stand-alone IR thermometer, which on the same wall reads 19.5).Changing the emissivity to the extremes, gets me at best at 6-7°C.QuoteThe sensor is on a separate PCB, which looks like it's from a different factory. And there's no trimmers, switches or anything the user could change, it must be done in software. I wonder if it's a problem with the model, with the firmware revision, or just my unit. I was hoping in a firmware upgrade but found nothing.The Uni-T site is useless, they just tell me to refer to the seller. There's no possibility to contact the technical lab or anything.And the seller says "the only solution is that you buy a new unit".This sucks because the unit would otherwise be good, sturdy and with a great thermal image quality, perfect for my needs...

author: Bill W
author_rank: Super Contributor
timestamp: March 01, 2023, 01:24:18 pm
content: 'Calibration' in this case is a gain and offset value for each individual pixel, stored in memory.However your problem is the same gain error across the whole scene, or you would get patterning on an even hot surface (eg hot cup close up). That leads me to either a bad factory calibration or maybe a bias voltage changed from build.Either way I reckon go for a card chargeback, noting the seller has already cut off their options by refusing to either refund or take a returnHope it turns out like this story about a bent table....https://forums.redflagdeals.com/credit-card-charge-back-dispute-aliexpress-2477207/Bill