Research On Portable Ammonia Gas Testing System Based On QCM

As a harmful gas that affects agricultural production,ammonia gas has been plaguing farmers and has attracted more and more scholars' attention.With the development of science and technology,there are many ways to test ammonia gas.However,most of them use chemical or optical methods.and these existing methods have certain limitations.For example,the equipment is bulky and has high environmental requirements;Therefore,it is urgent to design an ammonia gas test system that is light and small,has low cost,and meets the requirements for accuracy.the main work of this thesis is carried out around above demand.In this paper,QCM sensor and high-precision test system are mainly studied.Firstly,the circuit of QCM sensor is studied.During the experiment,a variety of start-up circuits were tested,and finally the gate circuit is selected as the vibration circuit of QCM sensor.In the whole system,QCM sensor is the data acquisition end,which transmited the frequency data,and then carrieed out the measurement through the high-precision frequency measurement module,and then transmited it to the main controller for processing.The portable device USES a 7-inch touch screen as the display terminal,which needs to display 8-channel QCM data at the same time.Meanwhile,the acquisition will affect the ambient temperature value of the sensor,so a storage analysis is required.The measuring accuracy of the equipment is 5Hz,which is corrected by equiprecision algorithm,and the display image has the function of automatic adjustment.The main work of this design focuses on the above objectives and indicators,and the specific work is as follows:(1)Complete the research and design of QCM starting circuit.Starting with the physical characteristics of QCM and combining with the previous technical related data and previous experience,the author studied a variety of QCM vibration circuits,conducted experimental tests,obtained experimental data,and counted the advantages and disadvantages of each circuit.Finally,the optimal gate circuit was selected as the vibration circuit of QCM sensor.(2)high precision frequency measurement circuit design is completed.In the traditional FPGA frequency measurement system,the accuracy of frequencymeasurement can only reach 50 Hz,which cannot meet the requirements of the system.This paper has carried out an in-depth research,selected high precision TCXO as the clock source,adopted the equal precision algorithm,combined with FPGA hardware sampling count,to achieve the 8-channel synchronous high precision frequency measurement module design.(3)complete the design of portable ammonia gas testing system based on QCM.After the above QCM sensor vibration circuit and high-precision frequency measurement circuit are successfully designed,the data collected by the test module are transmitted to the ARM main controller through the serial port.The main controller is connected with touch screen,FLASH,temperature sensor and clock chip.Through the PCB board design to make a prototype,soft and hard coordination to complete the development of various functions.(4)the system is used for ammonia gas testing and verification.Set up a standard test environment in the gas experiment,compared the standard instruments with the system for synchronous testing,collected data for data analysis,corrected various design defects of the equipment,and proposed the direction of equipment improvement.