Study On Quartz Crystal Microbalance Frequency Measuring System Based On DDS

The Quartz Crystal Microbalance(QCM)is a new measurement instrument which has great features of high sensitivity,selectivity and stability.It is widely used in physical,chemical,biological,food industry,environmental science,clinic medicine,and other fields.However,the fundamental frequency of most existing QCM sensors is mostly in the level of 5MHz?10MHz,and is usually operated with the oscillator method,with such method the oscillation will appear unstable and unreliable in the process of two phase flow measurement.It limits the application of QCM.For these problems,this thesis presents a new QCM measurement method with high sensitivity quartz crystal.The fundamental frequency of these quartz crystal between 30MHz to 50MHz.Experimental platform is build by hardware and software.This thesis firstly systematically introduce the background,the research status and the development of QCM.The work theory and implementation of QCM are discussed which gives the theory references for Circuit design.Secondly,based on the Direct Digital Frequency Synthesis(DDS)technique,the sweep signal is produced by AD9954.The STM32 processor are used to measure the impedance and phase of quartz crystal,Data collection and upload are realized by processor too.LAB VIEW software on upper computer is designed to process the data and display the measurement results.Finally,the validity of the designed QCM system is experimentally demonstally.Based on the measured results,the measurement precision is calculated.In addition,the reasons of the error in the liquid experiments are discussed detailedly.In the end,the improving methods are proposed.This thesis provide a reference for the application of QCM measurement.