Research And Design Of Quartz Crystal Resonator Testing System For Logistics Cargo Weighing

With the continuous development of the logistics industry and the rapid growth of goods transportation demand,weighing of goods as an indispensable link in the logistics industry becomes more and more important.In order to ensure the safety of transportation and reduce logistics costs,the research of weighing sensor and its measurement method has attracted more and more attention.The pursuit of higher stability and lower cost is the main development trend.Among them,quartz crystal resonators are attracting more and more attention due to their characteristics of high precision,high stability and low cost,and show good application potential in the field of cargo weighing.Its forcefrequency characteristics make its resonant frequency change with the change of force,so by measuring its resonant frequency can realize the accurate weighing of goods.Therefore,this paper studies and designs an accurate and low-cost frequency test system for quartz crystal resonators,and conducts frequency measurement and afterforce experiments on it.The main contents of this paper are as follows:(1)Establish the research object and the optimal afterforce Angle through theoretical analysis and modeling simulation.Based on the force-frequency characteristics of quartz crystal resonators,the influences of crystal tangent Angle,direction Angle and ambient temperature on the force sensitivity are discussed in this paper.Finally,the symmetric ATtangent non-holonomic disc quartz crystal resonators with the most significant frequency offset and the best thermal stability are selected as the research object of this paper.The optimum afterforce direction Angle was established by COMSOL modeling and simulation.(2)The frequency test system of quartz crystal resonator is designed to achieve the function of accurate frequency measurement.Based on the equivalent electrical model of quartz crystal resonator and impedance analysis method,the software and hardware design of quartz crystal resonator test system is completed in this paper.Firstly,in order to realize the interconnection and transmission between the electrical signals of the quartz resonator and the circuit signals of other modules,an interface circuit based on the automatic balancing bridge is designed to reduce the distributed capacitance caused by the leakage current,and thus reduce the measurement error.Secondly,Direct Digital Synthesis(DDS)sweep signal source was designed as excitation source for 5-20 MHz quartz fundamental frequency.Then,based on AD8302,a amplitude-phase detection module is designed to obtain the amplitude-phase of signals at both ends of the quartz resonator.Finally,a 12-bit data conversion module is designed to convert the analog voltage output of amplitude phase into digital signal,based on which impedance is calculated and resonant frequency points are judged.The experimental verification in this paper shows that the absolute errors of the quartz crystal resonator test system in this paper and the commercial oscillator circuit method are concentrated in 0-250 Hz,and the relative error interval is 0-0.003%.The errors are both positive,and the variation law of the errors is independent of the fundamental frequency of the quartz resonator,so it has good frequency measurement performance.In addition,it is verified in cargo weighing experiment that the sensitivity coefficient is 2.767Hz/g,linearity is 3.81%,lag is 0.52% and repeatability is 0.15%,indicating that the quartz crystal resonator,as the sensing element in weighing device,has good accuracy,sensitivity and stability,which basically verifies the feasibility and reliability of the study in this paper.And it has a good research prospect.