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Paint Line – Thick Coating

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.


  • Reduced sensitivity to changes in coating thickness and color.
  • Improved product properties.

The measurement becomes simple when the coating is thick enough to be highly opaque.  Most coatings are most opaque, least reflective, and have the highest emissivity value when measured using a sensor filtered in the 7.9 micron range (although a few coatings are more opaque at 3.43 microns).  In general, a coating must be at least 0.6 mils / 14 microns thick in order to be opaque at this wavelength.  This is a very thick coating by modern standards, but whenever the coatings are thick enough to be opaque, the model 48 (7.9 microns) or model 43 (3.43 microns), provides the best results.


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.


  Technical Features

  • Optimized Wavelength to minimize sensitivity to product and process variation.
  • Model 48 is filtered to measure thin film plastic coatings.
  • Model 43 is filtered to measure thin oil-or wax-based coatings & laminated films.


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.