Part 4: What type of detector is best suited for your application?
In part 1 of this guide, we explained how temperature measurement sensitivity varies based on the IR camera’s detector type. An additional point to consider is that different detector technologies sense infrared energy in different wavelengths or wavebands. Depending on your application, the waveband over which the IR camera senses energy can have a significant impact on measurement results.
If you look at Figure 2, you’ll see a typical atmospheric IR transmission curve. According to the figure, there is good IR transmission through the atmosphere at 7.5 μm to 13.0 μm and 3.0 μm to 5.0 μm. Thus, if your application requires you to look long distances through the atmosphere, then choosing detectors that operate in these transmission windows is optimal.
Figure 2: Atmospheric transmission for infrared energy
Similar thinking applies to other applications that involve looking at or through materials. For example, what if you want to measure the temperature of the filament of a lightbulb? To do this you would need to look through the bulb’s outside layer of glass. Looking at the transmission curve for the bulb’s glass (Figure 3), you see a spectral window that allows for the transmission of IR. To see through the glass and measure the filament will require a camera that senses in the 3.0 μm to 4.1 μm waveband.
Figure 3: Transmission curve of light bulb glass example
Figure 4 illustrates what happens when you look at a light bulb with a camera that senses within the glass transmission window. Thanks to the camera’s 3.0 – 5.0 μm InSb detector, you would be able to precisely measure the temperature of a light bulb filament.
Figure 4: Thermographic image of light bulb with InSb detector (3.0 μm to 5.0 μm) and < 4.1 μm filter
Figure 5 on the other hand, illustrates what happens when you look at a light bulb with a camera that operates outside the glass transmission window. Attempting to measure the filament using a 7.5 – 13.0 μm microbolometer camera results in temperature measurements from the glass surface of the bulb, instead.
Figure 5: Thermographic image of light bulb with microbolometer detector (7.5 μm to 13.0 μm)
To summarize, for certain applications, looking through materials may guide you to a specific detector based on its unique spectral waveband response.