Williamson Short-Wavelength Advantage
Infrared pyrometers rely on making a reading based on the amount of energy collected. The amount of energy collected can be affected by emissivity variance and optical obstructions. Selecting the shortest possible wavelength helps to eliminate variables such as emissivity variation and optical obstruction. Being less sensitive to these variables ensures for a more accurate reading compared to a general purpose long-wavelength sensor.Emissivity Variance
Every object emits infrared energy proportional to its temperature. Infrared pyrometers collect the infrared energy emitted by an object and convert it into a temperature value. Emissivity is the percent of energy emitted by an object compared to the theoretical amount of infrared energy emitted by a perfect emitter at the same temperature. The amount of energy emitted is a function of both temperature and emissivity.
Therefore, the emissivity of a measured target has a direct correlation to the energy reading of a pyrometer. Emissivity varies due to changes in material, surface texture, degree of oxidation, micro structure or surface contamination. The emissivity of a material can also vary at different wavelengths. The graph to the right shows that selecting the shortest possible wavelength will result in smaller errors due to emissivity variance. In fact, short-wavelength sensors can be 4-20 times less sensitive to emissivity variation compared to long-wavelength sensors. By reducing the errors caused by emissivity variation short wavelength sensors produce a more accurate and repeatable reading.