Probably you was referring to
this thread started by Fraser.
In the thread the author suggest how to build a rudimentary black-box "for the rest of us" to calibrate an IR sensor.
As I understand the key is the paint. A matt black paint. Because "all" matt black paint have a good emissivity value (0.90 or higher).
Even if not explicitly written, I suppose that after calibration the next step is to use the same paint on your target object to get a "good enough" value.
Since almost all stepper motor are "painted" with a not-glossy, no flat, layer of black material in the section between the front/back plates. I think that I should get a good value even with my not-calibrated chinese IR sensor when setting the emissivity value around 0.92.
Yeah, I will not get an error of +/-5 °C, maybe I will be around +10/-10 °C zone but in any case it will be enough to discover if the stepper is over-heating or not.
I found very interesting the article below published directly from the FLIR company. They are an authority in the field of thermal scanning.
"Use Low-Cost Materials to Increase Target Emissivity"https://www.flir.com/discover/rd-science/use-low-cost-materials-to-increase-target-emissivity/Among other things, they recommend the use of the
Scotch™ Brand 88 black vinyl electrical tape as a good way to increase the target emissivity to 0.96.
Also a stripe of
Kopton tape is listed as a good method to read temperature with an IR sensor, but the emissivity value is not reported.
I've found the emissivity of the Kompton tape (0.95) in the article here below:
"Engineers warm up to IR vision"https://www.edn.com/engineers-warm-up-to-ir-vision/I suppose that the Kompton tape has to be preferred when your dealing with very small IC components. Since it is very thin and does not affect the total mass of the target object in a significative way.
What surprise me is that the Kompton tape is yellow, not black. And it is semi-transparent too!
Excuse me now, I have to buy some tape!