| Dust concentration detection is one of the most important environmental monitoring methods.In many modern dust concentration detection methods,infrared detection is a continuous and real-time online measurement,and has the advantages of fast response and non-contact.The thesis is directed to the dust gas that has passed through the bag filter,and that has relatively low dust concentration.It is difficult to meet the measurement accuracy requirements in traditional dust measurement method.In the thesis,the backscattering method is used to measure the dust gas.Light backscattering dust concentration is measured by obtaining the backscattering intensity of the dust particle system to calculate the dust concentration.The thesis studies the dust concentration detection system based on Mie scattering theory.Because the visible light is easily influenced by external stray light,and its power consumption is large,the infrared light-emitting diode is used in the thesis.The driving circuit of the infrared light-emitting diode is simple,and the response speed is fast,with high luminous efficiency.In order to make the luminous intensity as large as possible to improve the accuracy of measurement,the infrared light source with relatively large rated current is adopted.And the frequency modulation of the optical signal can avoid interference of some clutter.The main tasks of the thesis are listed as follows:The dust concentration detection method and the scattering correlation theory are studied,and the scattering intensity distribution map under different particle sizes are simulated.The scattering angle of 90 degree is selected to receive the backscattered light.Based on this,the luminous flux distribution map of different lighting angle is simulated,and the 30 degree angle is selected.Finally,the measurement structure of the whole optical system is determinedThe constant current drive circuit of the detection system is improved,and the slow start function is added to prevent the high voltage causing damage to the light emitting tube.A light source driving circuit with stable current and adjustable frequency is designed.Based on the theory of phase-locked amplification,the orthogonal vector phase-locked amplifier is designed.Orthogonal vector phase-locked amplification can eliminate the effect of phase to the output value,and can effectively improve the signal to noise ratio.The signal processing platform based on STM32 is set up,and the upper computer display interface is written.In the laboratory conditions,the dust concentration monitoring system was preliminarily tested.The measuring range of dust concentration is 0-200g/m3,and the measurement error of dust concentration monitoring system is less than 7%. |
