Research On Cloud Water Content Detection System Based On TDLAS Technology

The detection of cloud water content is of great significance in the field of meteorological detection.In the process of artificial rainfall,accurate determination of the cloud water content in high altitude can effectively improve the success rate of rainfall and increase precipitation.The existing cloud water content sensors rely on particle,microwave,and hot wire measurement methods,but in practical applications,there are problems such as large volume,large power consumption,and low accuracy.Based on the Tunable TDLAS technology,an airborne cloud water content detection system is developed.The single board of the system realizes the functions of laser driving,harmonic signal processing and concentration inversion.It has the characteristics of high detection accuracy,small volume,fast response speed and good temperature stability.The specific research contents are as follows:(1)Building the overall design of cloud water content detection system.By analyzing the infrared absorption spectra of air components and water molecules,the 1368.6 nm distributed feedback semiconductor laser is selected as the detection light source.According to the temperature drift characteristics and tunable function of DFB laser,the driving signal synthesis circuit and the temperature control system based on MAX1968 chip are designed to stabilize the output frequency of laser.XMEGA64A3U microcontroller is selected as the main control chip,and the data transmission between the upper computer and the lower computer is completed by RS485 communication protocol.The design of current self balance detection system for preamplifier can effectively eliminate the DC component of detection signal and improve the signal-to-noise ratio.The design of PLL amplifier based on TLC7528 improves the stability of measurement and the ability of restraining noise.(2)Based on DDS technology and CPLD,the laser driving signal and the frequency doubling signal for harmonic extraction are synthesized.The fuzzy adaptive PID control method is used,combined with the laser temperature control circuit to adjust the TEC thermoelectric cooler,to stabilize the laser working temperature and ensure the detection accuracy of the system.In the development environment of Lab Windows/CVI,the upper computer program is written to realize the function of real-time data display and storage.(3)Building a test platform that can be used to measure the cloud water content.The system carries out real-time detection under different concentrations and temperatures,and compares with the measurement results of standard dew point meter.The experimental results show that the water content is in the range of 0-16 g/m~3,the error is less than 5%,the response time of the system is about10 s,and it can work normally under the condition of-55?+60?,which meets the requirements of airborne cloud detection.