ABSTRACT
Reliable online measurements of thickness (also known as gauge) are important to the production of many products that are sold in the form of sheets or films. Accurate gauge information is needed not only to control the process, but also for quality control. Variability in the thickness is especially problematic in electronic material applications—such as dielectric films for capacitors, where the changes in capacitance value are directly proportional to changes in the thickness of the film. Likewise, in optical applications the phase shift in transmitted light is determined by film thickness, and variations may cause unwanted visual effects. Gauge is traditionally measured in units where 100 gauge equals 1 mil (0.001 inches), or 25.4 micrometers. Sheet products are usually produced on a semi-continuous production line, and measurements may be made in the transverse direction (TD)—that is, across the width of the production line—or in the machine direction (MD), as shown in Figure 10.1. Film casting operation with a traditional thickness gauge based on attenuation of radiation. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315219950/2c7cd499-b5c3-4717-851a-9c7423677d32/content/fig10_1.tif"/>
