Importance

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Abstract

A non-contacting thickness measurement apparatus is described, which is capable of on-line, highly accurate web thickness measurements. The apparatus is comprised of a first and second distance determining means which calculate a distance value from each distance determining means to the web surface. The distance determining means are on opposite sides of the web, so each measures the distance to a different side of the web. At the same time, the distance between the two distance determining means is measured to produce a z-sensor spacing value. The two distance values are thereafter subtracted from the z-sensor spacing value to get a web thickness value. An x-y position adjustment means is used to keep the measurement spot on the web for the two distance determining means at the same location on the web, and several techniques are combined to eliminate temperature-induced and/or other unknown variations or drifts in the web thickness value which are not caused by actual changes in the thickness of the web.

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First Claim