Study On Photoelectric Salt Aerosol Concentration Sensor And Calibration System

Fog inhalation therapy uses special atomizing devices for powder atomization to treat various respiratory diseases.However,simple structures of existing medical atomization treatment devices result in the unstabitily of powder atomization,and the lack of powder aerosol concentration detection device,theoretical research leads to large administration error and affects treatment.Therefore,considering medical vaporizer specific requirements,physical and chemical characteristics of salt powder commonly used in fog inhalation therapy,proposing photoelectric salt aerosol concentration detection method based on light scattering,carrying out salt particle light scattering theoretical studies,developing dedicated salt aerosol concentration sensor and calibration system,could effectively promote fog inhalation therapy application.The main contents and results of this paper are as follows:Firstly,comprehensively analyzing particle detection methods and particle light scattering theory analysis methods,considering project requirements,chose super ellipsoid method to describe particle shapes,analyzed NaCl particle light scattering using T-matrix method based on discrete source,replaced surface integral in calculation by differential element method.Used matlab software to write main functions,and discussed the influence of T-matrix truncation coefficient N,element number,particle geometry parameter n0,a,b,c to light scattering intensity of randomly oriented salt particles.Regarding particle size distribution as logarithmic normal distribution,calculated scattering intensity of salt particle group with length of 0.4~6?m under different distribution parameters,providing theoretical basis for sensor structure design.Secondly,considering medical vaporizer structural characteristics,developed photoelectric salt aerosol concentration sensor with forward differential scattering light path,respectively collected reference light signal and two light scattering signals using photocells to compensate environment factors and smooth scattering function curve.Designed signal conditioning circuits for current-voltage conversion,amplification and filtration.Fabricated circuit board taking into account of layout,wiring,insulativity and anti-interference capability aspects.Chose low-dropout regulator chip TPS7A4700 forming sensor power supply circuit to reduce detection error.Achieved on-line detection of salt aerosol concentration and provided basis for salt atomization process control.Then,aiming at the influence of airflow velocity,particle adsorption,particle deposition in low-flowrate on sensor calibration,photoelectric salt aerosol concentration sensor dedicated calibration system which is comprised of salt atomization & uniformity cavity,calibration unit,measurement & control system based on LabVIEW platform,split plates and guide plates for airflow adjusting is built to achieve the purpose of rapid atomization,uniformity,mixture,low-flowrate salt aerosol simulation,and setting,collection,display and adjustment of flowrate and other parameters in calibration system.Finally,carried out performance tests of calibration system and salt aerosol concentration calibration experiments,flowrate effect experiments,performance tests of photoelectric salt aerosol concentration sensor.The results show as follows:(1)Humidity in calibration system decreased significantly in clean mode tests,and achieved the purpose of reducing humidity.In calibration mode tests,the speed of axial fan in salt atomization & uniformity cavity rangs between 1000~13000r/min,and control accuracy is about 100r/min;one the other hand,the flowrate in calibration unit rangs between 3~50L/min,and control accuracy is about 2L/min.These results indicate that calibration system meets the control requirements of salt atomization and salt aerosol rapid uniformity & mixture process of sensor calibration experiments.(2)Photoelectric salt aerosol concentration sensor nonlinear coefficient is 399.63 in calibration experiments.Sensor detection results are not affected by flowrate.Relative error of photoelectric salt aerosol concentration sensor for salt aerosol concentration detection in performance tests is 5.9%,satisfying salt aerosol concentration detection requirements.