You can get a fairly accurate measurement of a physical dimension of a thermal anomaly using your infrared camera. The procedure is as follows:
This procedure can be used when you need to measure the physical dimensions of a hot spot in your infrared image to determine the size of the area in question.
1. Find the FOV degree of your camera lens (given by manufacturer)
2. Convert from degrees to radians by multiplying degrees by .0175
3. Determine your distance from the object.
4. Find the field of view both horizontally and vertically at that distance by using this formula:
FOV = Angle in radians X Distance
5. To find a particular distance in the image,
a. Divide the FOV value horizontally and vertically by the number of pixels on your detector to find the area each pixel covers
b. Use the spot meter or line function to find the number of pixels for the area of interest. (You may have to use your software program)
c. Multiply the number of pixels in the area of interest by the size of a pixel to find the physical dimensions of the area of interest.
Tip provided by Wayne Ruddock
Advanced Infrared Thermography