However, the size of these devices do not match the space requirements for paper making installations.Ī further measurement method, which uses microwaves for measuring water weight in the forming section of the paper machine, has been described in detail in European Patent Application No.
In contrast to the foregoing devices, a single sided resonant microwave cavity sensor (ScanPro by Lorentzen & Wettre) is known, which more or less directly measures water weight. However, this device is disadvantageous in that measurement noise is high and that the measurement requires the use of radioactive material. Thus, this device provides essentially a “layer-thickness-measurement,” however, it cannot be used after the dry line.Īnother device provides a gamma backscatter based total mass measurement. 3,442,756 and 4,789,431 provides an ultrasonic measurement of the stock layer thickness by measuring reflectance of the ultrasonic sound from the top and bottom surface of the stock. This device measures the electric current through the stock and is sensitive to chemical changes in the stock.Īnother method described in U.S. One such device (Honeywell SpectraFoil) calculates the water weight based upon a measurement of the conductance of the stock layer on the former.
However, these device are limited in that the water weight is indirectly determined, i.e., calculated from the measurement of another parameter. Various devices are known for determining the water weight in the forming section. The present invention is directed to a sensor and process for measuring water weight in the forming section of a paper making machine using microwaves.
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