The method of measuring emissivity here is a reference method as described in ISO 18434-1.
The principle is to use a material of known emissivity to determine the emissivity of an unknown material. The reference material is placed on the sample and the sample is uniformly heated. The reference is then used to establish the true temperature of the material. Emissivity is them adjusted until the true temperature appears in the camera for the sample.
Step 1
Select a location to perform the test and measure the reflected apparent temperature of this location. Set this value as the reflected apparent temperature in the camera.
Step 2
Cover part of the sample with a material of known emissivity. Electrical PVC tape is very good, it has an emissivity of 0.95. The best is Scotch 33 black tape.
Step 3
Heat the material. The heating must be even, and you must heat it to at least 20 Degrees C higher than the ambient.
Step 4
Measure the temperature. Use 0.95 as an emissivity and measure from the tape. You need to remember this value, so it is best to write it down. You can use any measurement tool available in the camera, the spot is the easiest. I personally find area average the best tool for this, but it must be received and moved to fit within the tape.
Step 5
Move the measurement tool. You need to reposition it so as it is on the sample.
Step 6
Adjust emissivity until the true value appears. The tape and the material are the same temperature, you have already established this at step 4, so all you have to do is adjust the emissivity until that value appears. This is the emissivity value for this sample.
Tips
Always use a frozen or saved image.
Make sure your image is in focus.
Take care not to have any spot reflections in the image.
In the image above both measurement areas have been set at 0.95. They both read a different temperature due to the difference in their emissivities. The top area is placed on a reference material that has a known emissivity of 0.95, and the object has been uniformly heated. In the image below the emissivity of the bottom measurement area has been adjusted to read the correct temperature, this gives us the correct emissivity for the material. The emissivity of the material is 0.48.
Please note; emissivity measurements should be done at the expected working temperature.
