Polypropylene Plastic Film Thickness Measurement Using a Capacitive Sensor

Abstract

This article presents the development of a thin-film thickness measurement device for assessing the thickness of polypropylene plastic film prior to the sealing stage in plastic bag manufacturing. Leakage defects in plastic bags are commonly attributed to uneven sealing, often resulting from films with thicknesses exceeding 100 microns. To address this issue, a non-contact capacitive sensing system based on the AD7745 IC is proposed for measuring plastic film thickness during the manufacturing process. Experimental tests were conducted using 20 samples each of film thicknesses 70, 80, 90, and 100 microns. The results show that the proposed system can effectively differentiate overly thick films (>90 microns) from those of acceptable thickness (80-90 microns), with an error margin of approximately 5%. A linear regression analysis between the measured capacitance (dependent variable) and the film thickness (independent variable) yielded an R² value of around 0.9 within the measurement range of 70 to 100 microns.