The PROSIS Coating Weight Sensor is a cost effective and versatile solution for measurement of transparent, hydrocarbon-based coatings.
Sensors that use narrow-band filters mounted on a rotating wheel have been used to measure organic coatings in the past, but certain practical limitations exist with that technology. Specifically, because the filter wheel inside this type of sensor is rotating at the same time the sheet is moving, there is an inherent drawback of measuring in two different locations. This may cause measurable errors due to localized variations in oil distribution and substrate surface reflectivity, specifically on galvanized sheet. Additionally, since each type of hydrocarbon molecule possesses specific resonance wavelengths, any change in coating applied requires a physical change to the unique filters inside the measuring head.
PROSIS is a highly sophisticated coating thickness sensor for thin and ultra-thin coatings on metal strip using NIR full spectrum analysis. The sensor is a true online scanning spectrometer that simultaneously captures the Near-IR spectral signature. In general, spectroscopy is a method to analyze the correlation between matter and electromagnetic waves. PROSIS uses a proprietary detector array to measure the entire near-infrared spectrum simultaneously. With this technology, the system provides a long-term stable measurement and a high signal-to-noise ratio in one measurement location, making it immune to strip movement.
The sensor analyzes infrared absorption exhibited by hydrocarbon compounds in the material to be measured. The unique detector technology analyzes the full spectrum, instead of a few pre-selected wavelengths as in conventional IR sensor designs. Full spectral analysis, coupled with an extended infrared range, allows accurate measurements of coatings that were not previously available online.
By simultaneously analyzing multiple wavelengths, the sensor can discriminate between different product components, as well as distinguish between different substrate factors, which exhibit similar but not identical IR absorption. The measurement is designed to be insensitive to environmental effects. Proprietary techniques modulate the detector to the IR source, eliminating any interference from ambient light. Detectors are thermo-electrically cooled in order to maintain repeatable measurements even as ambient temperatures fluctuate.
The sensor assembly’s distributed processing enables the full spectrum to be measured rapidly, providing a measurement, which is insensitive to point-to-point formation variations in the coating. Conventional IR sensors, in contrast, exhibit up to a one second time delay between analysis points making them susceptible to errors due to coating and substrate variations.
This attention to the details of the measurement physics results in an oil film measurement that is extremely accurate and reliable, preserving sheet surface finish quality after stamping.