Moisture Measurements in Industry

Through a specialized capacitor we can achieve a device capable of being employed by commercial paper mills to measure and control the amount of moisture contained in a moving sheet of paper. By such control a mill can achieve dollar savings by producing more paper to exact specifications, and with less down time from paper breaks. Continuous monitoring of the moisture content of a fast moving web of paper can be made by using a spray or fringe field capacitor and a compatible electronic system. The basic principle involved is that the area and spacing factors of the capacitor have been held rigidly constant so that one variable is the dielectric. This dielectric is a web of paper that travels across a stationary capacitance measuring device. As the paper varies from a relatively dry to a wet condition the basic capacitance will change as the dielectric changes. If this varying capacitor is connected into a special voltage bridge circuit and the bridge is excited with 5000 cycles, the use of an amplifier, a 5000 cycle phase detector, and a mechanical feedback loop to a variable capacitor will rebalance the bridge to a null condition. With the rebalanced variable capacitor position connected to a pen the per cent moisture deviation of a web of paper can be read on a chart.