用于红外激光气体检测的数字正交锁相放大器的研制

发布时间：2018-05-29 09:54

本文选题：红外吸收光谱 + TDLAS　；参考：《吉林大学》2017年硕士论文

【摘要】：本论文选题来源于国家科技支撑计划课题:煤矿用红外CO检测仪(传感器)研发,课题编号:2013BAK06B04。煤矿环境下,需要时刻监测CH_4、CO等气体的浓度,以保障煤矿生产的安全。在众多的气体检测方法中,可调谐激光二极管吸收光谱(Tunable Diode Laser Absorption Spectroscopy,TDLAS)技术检测精度高、响应速度快、无需接触测量,被广泛应用。TDLAS技术中,用低频锯齿波信号与高频正弦波信号扫描/调制激光器,在检测仪后端,需要利用锁相放大器从气体吸收信号中提取谐波信号以表征气体浓度。商用锁相放大器价格昂贵、体积大、不便用于集成仪器中;本文研制了专用于TDLAS气体检测系统的数字正交锁相放大器,价格低、体积小、硬件电路简单、便于集成。首先,深入介绍了红外吸收光谱技术与TDLAS技术中的相关理论,包括朗伯比尔定律、直接吸收光谱(Direct Absorption Spectroscopy,DAS)技术原理、波长调制光谱(Wavelength Modulated Spectroscopy,WMS)技术原理、谐波检测原理、锁相放大器原理等,并利用MATLAB对理论部分进行了仿真,验证了所提算法的正确性。其次,设计了数字锁相放大器的硬件电路,包括光电转换电路、减法电路、AD采样电路、键盘矩阵电路、LCD驱动电路、SCI(Serial Communication Interface,串行通信接口)通信电路及DSP(Digital Signal Processor,数字信号处理器)最小系统等。再次,对数字锁相放大器的程序流程图进行了详细介绍,并对其中的两个中断、低通滤波、谐波波形显示等模块给出了具体的设计方案。利用Simulink建立了锁相放大器的功能模型并进行了用例测试。最后,开展了相关实验,测试了锁相放大器的性能。对单频正弦波信号提取谐波的实验表明,一次谐波的幅值与输入正弦波信号的峰峰值成线性关系。对模拟差分吸收信号提取谐波的实验表明,谐波信号的峰峰值与模拟气体浓度成线性关系。开展了CH_4气体实验,从差分吸收信号中提取了谐波信号,对气体浓度进行了标定,测试了检测系统的稳定性并计算了Allan方差。CH_4浓度为0 ppm时,所测浓度的波动范围为-61.2457 ppm~+84.4715 ppm;Allan偏差-积分时间曲线表明,积分时间为0.1 s时,1σ检测下限约为16.89212 ppm,当积分时间增加到3.8 s时,1σ检测下限降低为3.05046 ppm。本论文的创新点:1.自主设计并研制了专用于TDLAS气体检测系统的数字正交锁相放大器,其硬件电路简单,算法中只需存储少量参考信号幅值与数字滤波器系数。2.该锁相放大器可以作为数据处理和谐波提取模块,从而用于任何基于TDLAS技术的气体检测仪中,检测多种气体的浓度,具有普遍适用性。
[Abstract]:This thesis is from the national science and technology support plan project: coal mine infrared CO detector (sensor) research and development, subject number: 2013BAK06B04. In the coal mine environment, it is necessary to monitor the concentration of CH4CO at all times in order to ensure the safety of coal production. Among many gas detection methods, tunable laser diode Diode Laser Absorption spectroscopy (TDLAS) technique is widely used in many fields, such as high precision, fast response, no need for contact measurement, and is widely used in .TDLAS technology. Using low frequency sawtooth signal and high frequency sine wave signal to scan / modulate laser, it is necessary to extract harmonic signal from gas absorption signal by phase-locked amplifier at the back of detector to characterize gas concentration. Commercial phase-locked amplifiers are expensive, large in volume and inconvenient to be used in integrated instruments. In this paper, a digital quadrature phase-locked amplifier for TDLAS gas detection system is developed, which has the advantages of low price, small volume, simple hardware circuit and easy integration. Firstly, the related theories of infrared absorption spectroscopy and TDLAS technology are introduced, including Lamberbilt's law, direct Absorption spectroscopydas, wavelength modulation Modulated spectroscopy, harmonic detection, etc. The theory of phase-locked amplifier is simulated by MATLAB, and the correctness of the proposed algorithm is verified. Secondly, the hardware circuit of digital phase-locked amplifier is designed, including photoelectric conversion circuit, subtraction circuit and AD sampling circuit. Keyboard matrix circuit, LCD driver circuit, SCI Serial Communication Interface (Serial Communication Interface) communication circuit and DSP(Digital Signal process processor) minimum system, etc. Thirdly, the program flow chart of digital phase-locked amplifier is introduced in detail, and the design scheme of two interrupt, low-pass filter and harmonic wave display module are given. The function model of phase locked amplifier is established by Simulink and the use case test is carried out. Finally, relevant experiments are carried out to test the performance of the phase locked amplifier. The experiment of extracting harmonics from single frequency sinusoidal signal shows that the amplitude of the first harmonic is linearly related to the peak value of the input sinusoidal signal. The experiment of extracting harmonics from simulated differential absorption signal shows that the peak value of harmonic signal is linearly related to the concentration of simulated gas. The CH_4 gas experiment was carried out, the harmonic signal was extracted from the differential absorption signal, the gas concentration was calibrated, the stability of the detection system was tested, and the Allan variance. CH4 concentration was calculated when the concentration was 0 ppm. The range of variation of the measured concentration is -61.2457 ppm ~ 84.4715 ppm ~ (-1) Allan deviation-integral time curve shows that when the integral time is 0.1 s, the detection limit of 1 蟽 is about 16.89212 ppm, and when the integral time is increased to 3.8 s, the detection limit of 1 蟽 is reduced to 3.05046 ppm. The innovation of this thesis is 1: 1. A digital quadrature phase-locked amplifier for TDLAS gas detection system is designed and developed. Its hardware circuit is simple and only a few reference signal amplitudes and digital filter coefficients should be stored in the algorithm. The phase-locked amplifier can be used as a module of data processing and harmonic extraction, so it can be used in any gas detector based on TDLAS technology to detect the concentration of multiple gases.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN722

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