Low-cost sensor gauges metal thicknesses

The thickness of sheet metal products travelling at speeds of up to 5m/s can be measured rapidly and accurately using a French-developed system. Its manufacturer, Fogale Nanotech, claims that the system, based on a capacitive technique, is about a tenth of the price of alternative X-ray systems, as well as being faster and more accurate.

The device consist of two capacitive sensors mounted on the arms of a U-shaped stirrup, through which the metal product is fed. The intensity of the DC current between the sensors is measured to determine the capacitance and hence their distance from the product. From this, the product thickness can be deduced to an accuracy of 1-10 µm.

The system, which performs 50 measurements a second, can be used to monitor hot metal sheets and does to need to be recalibrated for different materials. Although the system was originally designed to measure the thickness of steel, it can also be used with poor conductors such as graphite. There is also a version for measuring the thickness of plastic and rubber films.