Various coatings, including dry lube, oil, clear acrylic, primer and a wide range of opaque coatings, are applied to steel or aluminum strip in order to protect the metal and to provide a value-added benefit to consumers. These coatings can complicate strip temperature measurement by greatly influencing the emissivity of the surface of the strip. For an infrared thermometer, coatings generally fall into one of three categories: those thick enough to be opaque, those thin enough to be transparent, and those in between that are translucent.
Because these sensors operate at a wavelength where the coating is highly opaque and non-reflective, these sensors eliminate the emissivity variation associated with changes in substrate material or with coating thickness. While most color changes have a very small impact on the sensor accuracy, some colors that use highly reflective pigmentation additives may have a lower emissivity value.
The Williamson sensors utilize the narrowest 7.9 and 3.43 micron filters in the industry. The use of a narrowband filter allows the Williamson sensors to measure thin films that are as much as ten times thinner than competitive brands. Therefore, when using a Williamson brand infrared thermometer the emissivity variation from one color to the next, or from the thickest to the thinnest coating is minimized, and changes in substrate material from cold band to hot band to zinc-coated to aluminum have no impact on the sensor reading.