The camera functionality check, more commonly referred to as the “tear-duct check”, is something we recommend thermographers do each time before they conduct an inspection. This is not a “calibration check” (that can only be done with a blackbody), but it can provide a quick and easy way for the thermographer to determine whether or not their camera is functioning properly and if further investigation of calibration is warranted.
How to conduct a “Functionality Check”:
- Power up your thermal imager and let it stabilize for 10 minutes.
- If your camera has multiple ranges, set it to "Range 1".
- Set emissivity to .98 and set the background temperature to an appropriate value for the conditions of the room you are using. One note regarding background temperature, it is best to conduct this check in a room that has a known or reasonably controlled background (i.e. it is probably best to be in your maintenance shop or home office, not next to the boiler, your woodstove or out somewhere in the plant).
- If your camera has it, be sure to check that the transmissivity adjustment value is set correctly (i.e. it should be "off" or set to "100%", but that depends on the infrared system).
- Turn on the SPOT or BOX measurement feature.
- At a distance of 1 meter (about 3 feet), save/freeze an image of a co-worker or partner's face with perfect focus, putting the spot or box temperature on/over their tear duct.
- You should read a temperature of approximately 34-36 C (93-97 F).
If the number you read is outside of those values, your camera may need to be checked for calibration. Please note, though, that a blackbody is the best way to check for calibration. If it is determined that your camera is in fact out of calibration, only the manufacturer can re-calibrate your system. It is not something that you can do on your own and will require sending the camera in for service.
The Functionality Check is Also About More Than Just Temperature:
Conducting a functionality check provides the thermographer with an opportunity to validate other important and critical settings on their imager prior to an inspection. This is especially helpful if more than one person is utilizing the camera. If there are more than one imaging system available, selecting the system that can obtain the accuracy required for the inspection. IE. What is the system accuracy (+ - %, such as the general of + or – 2% of total reading or + - 2°C @ 30°C which ever is greater) systems vary from 1% to 4% depending on manufacture. What is the spatial resolution? What is the measurement resolution? (distance that a target can be seen vs. measured?) So you know at what distance that you need to work within and be able to select the correct PPE for that inspection distance.
Parameters such as Range, Emissivity & Background/Reflected Temperature should always be checked before an inspection anyway. Variances in any of these can affect radiometric accuracy and possibly image quality on some systems.
This is also a good time, however, to double check the polarity of your color palette should your imager have this option. Is it inverted where white/brighter = cold and black/darker = hot? I’ll certainly never forget the time, early on in my career, when I told a customer that the hot water line in their basement was uninsulated…as it should have been because it was the cold water feed for the bathroom.
You also should make sure the temperature units (Celsius or Fahrenheit) and, on some systems, the “File Format” settings (i.e. are you saving 8-bit or 14-bit images) are what you want. If in 8-bit mode, typically a .BMP or standard .JPEG file on some models, you will not be able to adjust the level & span of your saved images.
Not to be overlooked... Are a few other settings and adjustments. Is your memory card inserted? Always check the card slot if you have removable storage. Is your battery charged? You should see how much power is left and throw in an extra battery before hopping in your car or truck and heading out to the job site. If your imaging system has the ability to utilize other lens assemblies, ensure that the proper lens is selected in the menu (in some imagers this is a manual setting, in others it is automatic when the lens is changed).
As you can see, the camera functionality check is really more about whether or not you and your imager are ready to do work. The temperature of a person’s tear duct, while important, shouldn’t be the only concern here. As such, you should make it a habit to conduct a complete functionality check on a regular basis. Not only will you have reassurance that you camera is functioning properly, you will also go out on an inspection knowing that your camera settings are correctly adjusted, reducing errors and avoiding imaging mistakes that sometimes could literally ruin your day or perhaps cost you time or money.