Development Of A Portable Low Frequency Lock-in Amplifier And Its Applications Of Infrared CO Gas Detection

This is supported by the national science and technology support program: “Infrar ed CO(sensor)used in coal mine”.The infrared gas detection method has the advantages of high sensitivity,high cost performance,high selectivity and so on,therefore,it has received widespread attention in the field of gas detection all over the world.This technology is one of the key technologies for the detection of weak infrared signal,it can extract a signal from strong background noises,It is very useful for developing infrared sensors.Based on this situation,this paper has developed a portable dual-channel low frequency lock-in amplifier,it is used in infrared carbon monoxide gas detection system.In the analysis of the research of infrared gas detection technique and lock-in amplifier technology at home and abroad,this paper firstly introduces the principle of infrared gas detection system,including: the principle of molecular infrared spectroscopy principle and lock-in amplifier.After introducing the principle of the detection system,this paper uses Simulink software platform to build a simulation system.The result confirmed the feasibility of scheme,and gives the hardware and software implementation scheme of dual-channel low frequency lock-in amplifier.The indexes of the lock-in amplifier are tested one by one by means of functional verification and carbon monoxide detection.Through the experiments,the results prove the rationality of the design scheme and the feasibility of practical application.The dual-channel lock-in amplifier can extract a minimum standard signal amplitude of 1 mV,when the phase difference is larger,the relative phase shift error is smaller,and the phase-shift error is below 0.2%under different phases.By using the prepared CO samples within the concentration range of 0—1000ppm,detailed experiments were carried out to derive the device's performances.As shown by experimental results,the limit of detection is about10 ppm,compared with the theoretical result,the relative measurement error is lessthan 15%.The concentration variation is-5.2ppm—6.2ppm for the measured CO sample with a concentration of 0ppm.By calculating the Allen variance,the prospective limit of detection is about 1.19 ppm.Considering the gas diffusion time in the gas-cell during gas preparation,the response time of the system is measured to be about 58—62s.Based on the above experimental results,the design of low frequency lock-in amplifier satisfies the requirements of practical application.The dual-channel low frequency lock-in amplifier shows potential applications by virtue of high performance-cost ratio,simple optical-path structure and easy to be embedded,etc.It has a good application prospect in the development of infrared gas sensor and weak sensor signal processing.