Microwave Sensors for Consistency Measurements in the Pulp and Paper Industry

摘要

In this thesis it has been shown that microwaves offer a new way of measuringconsistency in the pulp and paper industry. Two microwave methods were developed. The first method was based on a dielectric waveguide. The method was found to measure pulp consistency but it was sensitive to disturbing factors like flow velocity, pulp type and wood species. It was found that the reason for the poor measurement result was the separation of water from fibers near the sensing surface of the sensor. The method was found to be suitable only for applications where the components of the mixture cannot separate, as in the case of solutions. This sensor has found its use in the chemical industry. The second method was based on the measurement of the time delay of microwaves propagating through the process pipe. The time delay was determined by using FMCW techniques. This method was found to be insensitive to flow velocity, pulp type, wood species, freeness and fiber length distribution.