The “tear-duct test” is a recommended test to verify the calibration of your thermal camera. The suggestion follows that before the thermographer goes out to the factory floor to do a thermal scan (or house to do an energy audit/scan), he/she would turn the infrared camera on (also validating that the camera works and batteries are good) and look at a work partners face with a focus on the tear-ducts. The tear-duct shows the core body temperature (around 98.6°F or 37°C) and fluctuates very little, giving the thermographer a reasonable “base line” temperature to view. This test should be done with the same person each time for the best repeatable base line.
The purpose of this tear-duct test is to make sure that there isn’t any drift in the detector and that the resulting temperatures shown on the screen are within the specs of the thermal camera.
The tear-duct test should be a “thermal habit” of a thermographer and be done on a regular basis. There are two other tests that can be done at home or at the plant/office when the thermographer doesn’t have a “black body” source to test their camera against. On an annual basis, it is recommended that you do:
1. “Ice water bath” test—here you add ice and water to a bowl, stir it a bit, and the temperature will be 32°F or 0°C
2. Boil water where the resulting temperature will be 212°F or 100°C.
If your camera demonstrates little to no drift in temperature over time, the thermographer can have a strong sense that his/her camera is still in calibration. These tests don’t replace any requirements for camera certification by a certified lab, but are most certainly acceptable thermal practices in our industry!
For more information on how and when to implement a tear-duct test within your overall thermal inspection, reference our previous post on Planning to do a Thermal Inspection: Steps to Prepare You and Your Thermal Imager!