How to self-make a hot "black body" for gain calibration?

[hap2001]

Hi.
I've seen several posts of DIY black body at room temperature for NUC, even portable ones.
But what I want is a hot one for lens gain calibration, I remember Flir said that should be about 20K higher than ambient temperature.
It do not need to be accurate/precise, but must be temperature-even on a big surface, with high emissivity (low LWIR reflection).
After days of headache, I'm thinking of a container which I can pore in hot water, then it's surface will be hot and even, and be able to hold long enough for the calibration process... But I don't know the exact material I should use.
What do you guys think? Or any better ideas?
Thanks.

[Fraser]

Look for a Dahua Blackbody that was used for COVID fever detection. They can often be found cheaply on eBay. I paid £45 for the brand new ones I bought recently. You get a well made Blackbody that is capable of Ambient +5C to +80C (in my testing). You will then have a way to check your cameras flat field, and accuracy. Two pint point calibration is also possible.

If that does not appeal, you can easily make a simple plate type Blackbody for things like TAU core lens setup using just a metal box, aluminium plate, flat matt black paint, polyimide foil heater and a bench power supply. This is what FLIR offer for silly money !. I will upload pictures of the official FLIR Blackbody for TAU lens setup for you in a minute. I thought about making one for fun but I have ten Dahua Blackbodies so really no need for such a simple open loop heated Blackbody. The aluminium plate needs to be around 6mm thick to create a nice flat field image and the polyimide foil heater is available cheaply from eBay. It would be a fun weekend project and you could use a biscuit tin as the outer housing 

Fraser

[Fraser]

The FLIR simple “open loop” heated Blackbody for TAU FFC and Gain setup…..

https://www.flir.com/products/285-0029-02_12-v-blackbody-for-gain-cal/?vertical=lwir&segment=oem


I will upload pictures of the units interior…. It is very simple to copy 

FLIR’s comment on their 4” “Blackbody”……..

—————————————-
“Are there any considerations to using FLIR 4-inch blackbody sources?

Blackbody sources offered by FLIR are low-cost uniform temperature sources, and not intended for generating high-precision, highly stable temperatures. The source offered by FLIR is not a true blackbody and is not recommended for any sort of quantitative measurements.
 
It is a fairly uniform system to assist in performing flat field corrections (FFCs) and lens gain calibration processes with FLIR's OEM camera modules such as Tau2, Quark2, and Boson.
 
For optimal calibration of Flir Cores, it is recommended to use temperature controlled, high emissivity sources. SBIR and CI Systems offer a range of blackbodies for radiometric calibration, 2-point calibrations, MTF testing, and characterization.
 
 It is important to use 2 blackbody sources instead of 1 in many cases. Waiting for a blackbody to slew in temperature during a lens calibration or 2-point calibration is not recommended and has a negative impact on calibration quality.”
———————————

Fraser

[Fraser]

Pictures of a FLIR TAU FFC/Gain calibration Blackbody unit recently advertised on eBay for $700 !

The Polyimide foil heater is a WATLOW product but any heater with appropriate dimensions and wattage would be fine in this application.

Fraser

[Fraser]

Interior view....

[Fraser]

The paint that I use on Blackbody emission plates is Krylon Ultra Matt Black camouflage paint that was recommended to me by Bill_W. It was tested by NASA for emissivity and performed well. The colour of the ultra flat matt paint is not that important but I prefer to use matt black.

To create a temperature controlled Blackbody you can just add a simple low cost PID temperature controller that provides PWM output drive to a SSR. It will not be as good as a well designed Blackbody but it may meet your needs. For me, the availability of cheap new surplus Dahua Blackbodies placed all my Blackbody build on hold as I now have all the Blackbody units that I could ever need and they are easily modified to meet future needs. I am also fortunate to own several professional Blackbody units for more demanding tests. Professional Blackbodies are eye wateringly expensive so the Dahua or Hikvision Fever screening Blackbodies are a real bargain if found at a good price. I can use several to create a multi point calibration that is more accurate than a simple 2 point calibration.

https://www.eevblog.com/forum/thermal-imaging/danua-reference-blackbody-under-the-covers-)/

Fraser

[Fraser]

On eBay USA I see two Dahua Blackbody units for sale at $99 at the moment. Not the best price that I found during my past searches (best was £45 each new and unused) but I did pay over $100 each for the first two units I bought just after the Pandemic abated. Considering the good build quality, use of a high quality name brand PID temperature controller and the saving of time/effort to DIY a unit, these are very good value for money if a temperature exceeding 80C is not required. Operation above 80C is possible but requires modifications to the plate insulation materials.

https://www.ebay.com/itm/265850019122?

https://www.ebay.com/itm/195229126071?

Note that there are two versions of these Dahua Blackbodies....the silver cased (JQ-D70Z) model is the Mk1 release that was a fast response to a market need. The white cased (DH-TPC-HBB) model is the MkII and is a more refined build as may be seen in the previously referenced teardown I did on the two types. Whilst both work well, I recommend the white cased DH-TPC-HBB model as its build is superior.

[Fraser]

Regarding the OP’s idea of a hot water bath…..

Sadly such a baths top water surface is a very non-flat target due to thermal currents cycling within it and thermal loss at the edges. Water bath Blackbodies tend to comprise a vertical water tank with closed loop heater control and water stirrer to keep the water moving. The test target/emission plate sits on the side of the water tank and is directly heated by the water. The water stirrer is essential to reduce the thermal gradient that would normally occur within the water column. Not the most portable or user friendly type of Blackbody and not one that I would use or recommend for anything outside a laboratory setting.

Fraser

[IR_Geek]

... Two pint calibration is also possible. ...

I always enjoy a "Two pint calibration" as well 

Excellent information as always Fraser.  I'd just add that you can put some high temp non-flammable insulation behind the heater pad to help stabilization and potentially reduce power draw.   The large the size the more helpful the insulation will be.   

[Fraser]

Ooops, thanks for spotting that ….. A pint of something alcoholic certainly does help with the boredom of waiting for Blackbodies to temperature stabilise 

I forgot to mention…. The Dahua Blackbodies may be used in an ambient temperature mode by just setting the PID to a temperature below ambient. The PID displays the current (ambient) temperature of the emission plate and does not try to drive the heater. Decent quality PID controllers are used in these units but a more accurate thermometer may be employed in the test as well. If you have two identical models of Blackbody you are assured of the same emission plate Emissivity for the two point calibration. This can be important for accurate calibration.

Decent Blackbody units may also be used for refreshing the calibration on some thermal cameras and as part of the dead pixel mapping process. A very useful tool to have even if not used regularly. Affordable surplus stock Blackbodies are another positive to come out of that awful pandemic (along with surplus affordable fever screening thermal cameras).

Fraser

[hap2001]

Fraser, you are back!
Thank you a ton.
Lots of high quality infos as always!
I need some time to digest them 

[_Wim_]

If 60°C is sufficient, you could also go this route: https://www.eevblog.com/forum/thermal-imaging/anyone-have-an-estimated-emissivity-for-the-ivac-9000-radiators/

[babysitter]

Inside holes, magic is going on resulting in the hole having a emissivity factor of 1, paint or coating doesn't play a important role. This is true also for a hole in a bucket full of wet crushed ice slush (when there is enough but not to much water on the ice.) Check old NBS circulars, that is the best chance of the place where I have read this, my brain runs on 3 cylinders due to the flu.

Have fun!

Hendi