We see ourselves: Mirroring
Handhelds are incredibly convenient, portable and easy to use – but there is always the user’s body behind the meter! Many surfaces “mirror”, i.e. reflect, the incident heat radiation – and thus we can virtually measure ourselves. That’s why I usually use a sturdy and vibration-proof gooseneck tripod with a solid base.
Certain surfaces – especially metals – are incredibly reflective, even if they have been coated with paint. As the thickness of the coating decreases, it quickly reaches a transmittance high enough to cause such distortions. Since humans have a significantly higher body temperature (if they are healthy and still alive), errors are always pre-programmed here!
The room temperature: We first calibrate ourselves
Not only the camera has to be “looked over” from time to time, but also the daily environment has to be right! In order to achieve comparable results, we work with a fixed room temperature of 20 to 22 °C. This means that, depending on the season and the benchmark process, we even have to keep this value as constant as possible by heating or cooling the room several times. For this there is an air conditioning system and constant water temperatures with chiller
In addition to measuring the switched-off system at the start of our measurements, we also use a matt-black painted copper box as a second reference (emission factor 0.99), which is located close to the test system and has a very accurate and calibrated temperature sensor. With this I can always start the comparison measurements to be really sure.
From slant to slant brings muck
As tempting as it may be to quickly “shine a light” somewhere – the values obtained in this way are usually much too low! You will not be able to avoid unscrewing an object yourself or – if this is not feasible – it is better to do without this type of inaccurate evaluation altogether. The following example with two different angles (perpendicular at 90° and acute at approx. 30°) shows what I mean by this:
Despite painting with my special paint, which I will come back to in a moment, the values are simply no longer correct if the angles are too acute:
Apart from the fact that we cannot increase the “depth of field” with aperture tricks, as we are used to from a normal camera, the radiation of heat is not the same (strong) in all directions. At below 15° we then get only absolute binary decay. Now let’s move on to our “poison cabinet”, where we keep a few little secrets as well as a very expensive liquid that will help us rule out any further measurement inaccuracies.
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