Device for checking the thickness of dielectric sheet material

Abstract

Abstract 1. Device for testing the dielectric properties of sheet materials, especially for testing banknote watermarks, comprising : - means (11) for moving the material to be tested (10), an oscillator (15) with a stable frequency ; - a set of capacitors (131, 132 etc.) formed of pairs of flat foils (121, 122, etc.) with a relative determined configuration, between which the material to be tested passes, each capacitor (13) being connected to the terminals of the said oscillator (15) through a load resistor (16, 161, 162,... 16n) respectively ; - a set of circuits (17; 171, 172, etc.) to amplify and rectify the ac voltage at the terminals of each of the said low resistors (16) ; - a multiplexing circuit (18) with its inputs connected to the outputs of the foregoing unit ; - means of analog-to-digital conversion (19, 19') connected to the output of the multiplexing circuit (18) to generate a dynamic measurement signal relative to a zone of material (10) passing between the foils (12) of one of the capacitors (13) ; - a memory (21) which records the said measurement signals read during the passage of a standard material, and - means (20, 22 and 22, 25 and 29) adapted to control the combination formed by the multiplexing circuit (18) and the means of conversion (19; 19') synchronised with the means of travel (11), to make a comparison between the measurement signals generated by the means of conversion (19, 19') during the examination of a zone of material (10) and the signals read in memory (21) relative to the same zone of standard material and, to determine by correlation a validity signal (S) of the tested material (10).

Inventors

• 👤 Dominique Jeanneau
• 👤 Jean-Loup Poilleux

Bibliographic Details