Do infrared cameras measure temperature? No, they don’t measure temperature. I’ll explain: Thermal imaging cameras and spot radiometers detect the thermal radiation emitted by a surface, so they don’t actually measure temperature. There are ways to directly measure temperature with thermocouples, RTDs, thermometers, and so on. Thermal imaging cameras and spot radiometers are just sensitive to the thermal radiation, and that is what they measure. Therefore, you have to be very careful when you perform a test because, even though you can see a temperature scale with the colors, it is the emissivity of the surface that determines how the heat is radiated from that surface. Unless you’re taking that into account, we are not reading temperature.
So how much does that matter? When I’m performing tests that compare A vs. B vs. C, I’m comparing like things together. They’re supposed to be the same temperature, and I can see that one is hotter and one is colder. Or if I’m comparing “before” and “after,” even if my reading of Celsius or Fahrenheit is not correct, at least I can see it has changed—as long as the test conditions, the settings, and everything else are the same, which is a big deal.
In this case, I can see that this bearing (yellow-white in video) is clearly much hotter than that bearing (violet), and I can ask myself whether it should be that way. It doesn’t necessarily matter what the temperature is, as I can see it’s clearly much hotter. I can see a difference between this one and these two (yellow pipe vs. orange pipes).
This is a slightly different example, but here’s a tank, and the infrared image shows the bottom of the tank is much cooler, and the top of the tank is much hotter. So this might be used to check the level in a tank or detect a buildup of something. It’s still very useful to perform the infrared measurements, but the exact temperature may not be accurate, and it may not matter.
In this case, again, we have a thermal image of a motor sitting on a pump, and I can see that it looks hot, but you can adjust the temperature scale to make almost anything look hot. I can just tell you that, in my professional work, I’ve seen people take thermal imaging readings and jump to huge conclusions about what they measure—assuming something is terrible and needs to be repaired or replaced, and they perform all kinds of work to find out there was nothing actually wrong. It was just the settings of the camera. So you need to make sure you understand how to use an infrared camera before you start using it to make these sorts of decisions.
If you look at the video on emissivity, you’ll see how you can get a measurement of temperature.