Research On Key Issues Of Infrared CO Detection System Based On Quantum Cascade Laser

Mining in the difficult areas can easily lead to gas leakage and coal dust spontaneous combustion and other major security incidents.So it is of great safety to develop a sensor that can accurately detect the concentration of carbon monoxide gas in real time.The application of infrared spectroscopy absorption technology for the identification of toxic gases is the main trend development of mine gas detector.Compared to the other infrared spectral absorption technologies,using the quantum cascade laser of good monochromatic and quasi-straightness as the light of infrared detection system has much more advantages,such as stronger ability of gas molecules identification and higher measurement accuracy.Thus this subject has very important research significance.There are two key problems in the gas detection system based on pulsed mid-infrared QCL:firstly,apply the pulsed lock-in amplification technology to accurately extract the output signal;secondly,effectively control parameters of the gas absorption cell,such as temperature and pressure to achieve the precise detection process.This paper has done the following work based on that.First of all,design a narrow pulsed lock-in amplifier,composed of the narrow-band filter circuit,multiplier circuit,low-pass filter circuit and so on.And carried out detailed functional verification experiments,the results show that the narrow pulse lock-in amplifier has a good frequency response(center frequency 5k Hz),lower pass-band width(bandwidth 80Hz),higher linearity(fitting degree of 98.043%).Second,control a variety of parameters of the infrared absorption cell,including the temperature control unit and flow control unit.The temperature control experiment of stainless steel cavity is carried out using Fuzzy-PID compound control theory.The results show that the temperature control system has a fast response time(response time 7mins)and a low steady-state error(control accuracy ± 0.2 ?).And the flow rate of the simulated gas cell is controlled by the mass flow meter.The results show that this unit can realize the flow control function with good repeatability and error about 5% of the full range.Finally,the CO gas calibration experiment is carried out on the complete CO detection platform.The results show that the phase-locked amplifier can effectively detect the gas concentration of CO when temperature and flow rate of the infrared absorption cell are selected.Furthermore,the system has high detection accuracy and good stability.