Mass Flow Rate Measurement Based On Microwave Sensor

Metering the mass flow rate of bulk solids is becoming increasingly important inchemical production, coal transportation, food processing. Although there are manymeasurement methods of solid mass flow rate both at home and abroad, such as directmeasurement, capacitance method, acoustic sensing method, tomography method.However, these methods lack either precision or real-time performance. As a newmeasurement method, Microwave sensor is becoming more and more popular in theworld because of its strong penetrability, quick response, easy installation, low cost.But there are still some technical problems, the limit of moisture in measurementprecision, the extraction and processing of signal for large number of particles. Toresolve these problems, based on the principle of microwave method in measuring thespeed of solid particles, this thesis studies the core issue of metering the mass flowrate of bulk solids. The main research work and the results are as follows:1. Aiming at the measurement method of volumetric concentrations of solids,this thesis puts out two defects, which are poor accuracy, humidity influence. Toresolve these problems, we start from wave propagation equation, combineattenuation coefficient and phase shift coefficient with concentrations of water, air,solid, get each phase concentrations of mixture through simulation with C++. Thisalgorithm solves the problem of humidity influence in concentration measurement. Inaddition, when water concentration is fixed as0.283, the volume fraction of solidsand gases can be determined by microwave amplitude and phase information;2. It is difficult to get the average velocity of solid particles from the Dopplerprinciple. As the number of particles increases, there will be different frequencycomponents in Doppler signals, which could not reflect the rate of movement of theparticles. To resolve this problem, this thesis adopts fast Fourier transform,discretizes time domain signal, averages the weighting signal amplitude in frequencydomain. In this way, we get the average velocity of solid particles. In the experiments,average velocities of mass solid particles are found much smaller than theoreticalvelocity. To analyze the influence factors on velocity, we change signal in timedomain to signal in frequency domain, extract the frequency shift of single particle,obtain the velocity from Doppler’s principle. Through the experiments, interaction is found much bigger than the influence of pipeline impact, as well as air friction.3. After theoretical analysis, experimental verification, we get the linearequation of power and mass. During the experiments, installation position of antennais proven to influent the power measurement. To resolve this problem, we putforward multi-antenna measurement technique. The method of mass-power can betreated as an exploration, which can be used as a verification of Microwaveconcentration-velocity method in measurement of mass flow rate.