Research On The On-line Measurement Of Paper Moisture Based On Microwave Cavity

Paper moisture is an important parameter in paper production, it is the mainindicator of paper quality. Keeping paper moisture stable is a basic requirement toensure paper quality. On-line measurement of paper moisture can fully reflect thereal-time distribution of paper moisture, it is the basis of paper quality control system.There are two main ways of paper moisture online measurement, infrared andmicrowave. The microwave has a strong penetration, so it can be used in on-linenondestructive measurement of high-weight paper moisture.The method for on-line measurement of water content described in this thesis is themicrowave cavity perturbation method. The microwave cavity perturbation refers to thatit will produce perturbation to electromagnetic distribution and change the resonantfrequency of the microwave cavity when dielectric constant of the medium within themicrowave cavity or the configuration of the microwave cavity changes appreciably.Thus the change of paper moisture in the microwave cavity will lead to the change ofdielectric constant of the medium within the resonator, and it ultimately will reflect tothe resonance frequency. The resonator measuring system achieve on-line measurementof paper moisture by the detection of the resonant frequency.The thesis develop the measuring system in accordance with the requirements ofproduct performance in this project. At first, we work out the overall design, thencomplete the work of design and debugging in allusion to the specific requirements foreach module. This thesis design and debug software program with reference to theworkflow of the system. Finally we test the overall performance of this system byexperiments. This design mainly includes:1. Design the integrating circuit to supply a scanning voltage for the system.Reasonable control of the scanning voltage allows to reduce the interference of theclutter pulse.2. Design the differential circuit to extract resonance pulse edge. Reduce theinterference of the clutter pulse and environmental noise by debugging differentialcircuit and designing differential lock link.3. Design the probe temperature controlling circuit. The measurement of the water content of the paper could be affected by temperature, so we maintain the probetemperature at the set value. We achieve feedback control of the probe temperature bythe PID algorithm.4. Design the main control circuit and the software system to achieve the controllogic of the system. Design the man-machine communication module to adjust thesystem parameters. Design the signal transforming module to make the output signal ofthe system meet the requirements of the design.As the system uses microwave measuring technology, it can be applied to on-linemoisture measurement of specialty paper, high-weight paper and cardboard.