Today I want to say a few more words about the use of infrared thermometers for taking temperature readings of hydraulic stuff.
These gadgets are great little tools, but they have limitations, and apparently, some people are still unaware of them. After watching another tech point his "laser thermometer" at a shiny gear pump and then proclaim that it is "cold", I decided that another "show and tell" on this topic is desperately needed.
There are two basic reasons why an infrared thermometer will give you a false reading.
First - most of these thermometers assume a certain fixed emissivity of the measured surface. Emissivity is a material's ability to emit radiated energy at a given wavelength. The problem arises due to the fact that highly polished metals have a very low emissivity, and a lot of industrial hydraulic things come with a shiny finish. Here's a nice example for you:
This is a common gear pump, with an aluminum body and a relatively shiny finish, and I "took the liberty" of spraying half of it with black matte paint.
This is how the pump looks when you look at it through an infrared camera:
Yes, the suction side of the pump is hotter (due to the internal slippage), but you can clearly see that the shiny aluminum half of the body reads at almost room temperature, while the painted half reads close to 50 ºC. That is a low emissivity surface for you.
By the way, if you don't want to paint your client's hydraulic equipment, you can always use a piece of dark scotch tape - it doesn't even need to be black:
See the difference? If you say that your gun is an advanced model that allows you to introduce the emissivity coefficient for "error correction" - let me stop you right there. It's a nice feature, but it is virtually useless. First of all - it is inconvenient, and I assure you that you will get tired of using it very fast, and second - shiny surfaces, aside from having low emissivity, also have great reflectivity, which means that by pointing your thermometer at a shiny surface you may actually be reading the temperature of the reflection of something else. Make your life easier - use the scotch tape trick. Works every time.
Now - the second reason why an infrared thermometer can fool its user is the fact that the red dot that you are seeing and the spot the infra-red sensor is "looking at" are often not coincident. I shouldn't say often, I should probably say always. If you don't take this into account - you can get a false reading. And there isn't a thing like "all infrared guns are calibrated so that the measured sport is always below the red dot" Nope. Some will be above, and some will even be to the side, especially if you drop your tool a couple of times "in real industrial conditions".
My "heat gun", for example, reads the spot that is slightly lower than the red dot at this distance:
So, if you want to trust your temperature readings, you must know the limitations and "aiming peculiarities" of your infra-red thermometer.
Or, you know, get a FLIR camera or at least a smart phone that has one...