I continue to see many folks on various messageboards who seem confused about the issues of sensitivity and resolution. Both are important to understand so that you can buy or use a camera that fits your needs.
Thermal sensitivity is a measure of the smallest temperature difference that can be seen with a camera. There are several ways to characterize it but most typically it is called either "sensitivity" or "NETD" (Noise Equivalent Temperature Difference). Most cameras now can, in theory see a 100mK difference, i.e. they can distinguish between a blackbody surface at 30C and one at 30.1C. This is good enough for most condition monitoring applications. For buildings a more sensitive camera means you can see more and see it more often. A sensitivity of at least 70mK is recommended, meaning you can, in theory, distinguish between 30C and 30.07C. The increased sensitivity, while it seems small, is not linear and is, therefore, quite significant.
Resolution can be broken into two specifications: spatial (what you can see) and measurement (what you can measure radiometrically). Resolution depends on the size of the detector array (80x80, 160x120, 320x240, etc) AND the lens AND the distance to the object you are looking at. A wide angle lens will have less resolution than a telephoto lens on the same camera. Consider what field of view (overall image you are seeing) you need; for example inside a house, you want a fairly wide field of view while on the exterior of a highrise building you probably want a narrower one. And then think of the detail you need to see at your working distance. If you need a wide field of view and great detail, you want a larger detector array. Measurement resolution is exactly the same, EXCEPT you need to be roughly 3X closer or have the "target" be 3X larger to make an accurate measurement.
We have some great webinars that go into much more detail on all these topics and, of course, they are covered in both Level I and Level II courses. I hope all this give you something to think about as you enjoy a cup of coffee this morning!
Thermally Yours,
John
ASNT NDT Level III #48166
The Snell Group
www.thesnellgroup.com
www.thermalsolutions.org
800-636-9820