How Can I measure the transmission rate of an infrared window?
A. It must be noted that specialised instrumentation is used to measure the spectral transmittance of IR window materials, however as the majority of thermographers are unable to access this type of instrumentation we have to derive methods of using our IR cameras to calculate the approximate transmission rates. I have used this method in the field many times and it has proven to be accurate and reliable, we call it the “coffee cup test” Method 1: IR camera with external optics transmission compensation: 1. Using electrical tape mark a low emissivity target onto a coffee cup and fill the cup with hot coffee. 2. Set the transmission rate to 0.99 and the emissivity to 0.95. 3. Measure the temperature of the emissivity target on the coffee cup. 4. Place window in front of target. 5. Calculate the IR window transmission by adjusting the camera transmission rate until the temperature reads the same as the temperature without the IR window. 6. Mark transmission rates on IR windows. Method 2:
