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MOISTURE SENSOR Disclosure Number: IPCOM000025186D
Original Publication Date: 1983-Dec-31
Included in the Prior Art Database: 2004-Apr-04

Publishing Venue

Xerox Disclosure Journal


A non-destructive method for measuring the moisture content of a sheet of paper 13 or other materials that changes its dielectric properties with the absorption of water is described. The material 13 to be tested is placed in the air space between two electrodes 11 and 14 as shown in Figure I. Depending on the application, the material may or may not come into contact with the electrode, but generally there is an air gap 12. As the moisture content of the paper 13 changes, so also does the dielectric properties. A technique for detecting change in the dielectric property of paper is shown in the equivalent circuit of the moisture sensing device 10 depicted in Figure 2. The device 10 is made part of a sensitive bridge circuit 17 which can be balanced to the ambient condition with signal generator 15 and lock-in Op Amp 16. As the paper 13 takes up or loses moisture, the dielectric properties of the paper change, along with the collective AC impedence of the device. This unbalances the bridge, changing the input to the Op Amp 16. The primary advantage of this technique is that it is a real time, inexpensive, non-destructive test for moisture variation.