Infrared windows are often used to allow us to inspect through an opaque solid material. They are made from various materials and are very useful where no other option exists. This blog looks at some of the known issues and is really just my opinion.
Choice of material;
There are many different materials available, the two most common are BAF2 and CAF2. CAF2 is more suitable for MWIR cameras, and BAF2 is more suitable for LWIR cameras. A third polymer material is also commonly available. These are fairly fragile materials, and it is not really clear how they perform over time, but it must be assumed that exposure to light over long periods will change the transmissivity of these materials. The external cover should be left closed to protect the window from damage by light, and to add mechanical strength.
These are perfect for fitting by manufacturers to new equipment, but retro-fitting them to existing equipment does have problems. While the windows themselves are certified, as is electrical switchgear, the fitting of the window retrospectively would not be. So retrofitting them would invalidate any certifications that exist, and the switchgear would have to be re-certified, which is expensive, and sometimes impractical.
ARC Flash protection;
The arc flash rating and indeed all the certification is tested, and this is done on sample windows under specific conditions. These tests are done with the front cover CLOSED, and this does surprise people. This means that if an arc flash occurs when a thermographer is inspecting through a window, the material could literally blow up in his face. Personally I wonder about the logic of windows at all, if this is the case. Surely a hole with a fitted cover would offer a cheaper alternative, and offer just as much protection. The choice between a polymer or crystal window to me is like being asked to choose between something that will melt into your face, and something that will shatter and embed itself into your face. I have often wondered why they don’t just make windows without the crystal or polymer, just a frame and a front cover.
Seeing through a window material is one thing, measuring through it is something totally different. While this can be done, it is more difficult than first appears, and produces more errors than is expected. You must measure the transmission rate for the window
Mesh type windows;
You cannot measure through a mesh.