We are often asked this question in our infrared certification classes. There are a number of important reasons...to detect certain gasses including methane, to better measure the temperature of glass (it has a high emissivity, >.90 in MWIR) and to minimize reflections when inspecting certain low-slope roof membranes.
It also allows us to successfully inspect inside a furnace because mid-wave cameras can see clearly through flame at specific mid-IR wavelengths, something that a long-wave imaging system does not provide due to the radiation transmission properties of fire. This capability improves the accuracy of temperature readings and allows for better analysis of thermal patterns when evaluating the efficiency of burners, capturing the temperatures of tubes or detecting the build-up of coking.
Check out this short video clip from last year's InfraMation conference which nicely demonstrates the transmission differences between long-wave and mid-wave cameras when inspecting furnace tubes:
The presenter, Andy Whitcher, is actually returning to this year's conference in Las Vegas to speak about Optical Gas Imaging this time around. More on that in another post. For now, enjoy this video and then make plans to join us at the Rio Las Vegas in September for InfraMation2016; the industry’s largest thermal imaging applications and networking conference. I hope to see you there!