TDLAS Breathing Gas Detection Temperature Control System Structure Optimization And Control Software Design

Breathing gas diagnosis technology diagnoses diseases by detecting specific abnormal components in human exhaled breath.It has the advantages of noninvasive,rapid and safe,and has broad clinical application prospects.Tunable Diode Laser Absorption Spectroscopy(TDLAS)has obvious comprehensive advantages in detection sensitivity,system stability and operation and maintenance cost,and has great potential for application in respiratory gas detection.The temperature stability and power consumption of the mid-infrared TDLAS laser temperature control system have an important impact on the gas detection sensitivity and overall power consumption.This paper systematically optimizes the design of the temperature control system structure and control algorithm.In order to prevent the laser from being directly affected by the variable air environment,a two-stage temperature control structure with two-stage Thermoelectric Cooler(TEC)as the core that control the temperature of the laser chip and the laser's case respectively is designed.The two-level TEC device selection is based on the principle of TEC's low-consumption and high-efficiency application,and the overall structure is optimized through the adjustment of the materials and dimensions of each component in the temperature control system.Based on this design method,the structure of the semiconductor laser temperature control system is designed based on the temperature control requirements of the CO gas detection laser.FloTHERM simulation results show that the coefficient of performance(COP)of the first and second TEC of this temperature control system reaches 8.0 and 10.17 respectively.Aiming at the above-mentioned two-level temperature control structure,a temperature control algorithm with fuzzy PID algorithm to control the temperature of the laser chip and classic digital PID algorithm to control the temperature of the laser casing is designed.The transfer function of the temperature control system was obtained by the identification of the experimental test method.The control program of the host computer is written in Python language,which visually displays the monitoring of two-level temperature changes,TEC current drive,laser drive current and other parameter information.The control program of the host computer also realizes the online adjustment of fuzzy control rules and temperature control algorithms.By combining the algorithm-optimized upper computer control program with temperature detection,TEC drive and other lower computer circuit modules,a complete temperature control experimental system is constructed.Experiments show that the system can quickly stabilize within±0.01? of the set value in the range of 10?50?,and has high energy consumption efficiency,which can meet the temperature control requirements of CO detection semiconductor lasers,and is also the overall performance of the mid-infrared TDLAS system.Optimized design provides guarantee.The establishment of the optimized design method of the related mid-infrared semiconductor laser temperature control system has laid the necessary technical foundation for the research of breathing gas detection equipment.