数字正交锁相解调算法在可调谐激光光谱密封药瓶水汽浓度测量中的应用

Detection of Water Vapor Concentration in Sealed Medicine Bottles Based on Digital Quadrature Phase-Locked Demodulation Algorithm and TDLAS Technology

密封药瓶内的药物在储存过程中,时常会因为保存方式不当,产品质量不合格等问题导致其气密闭性变差,极易与空气中的各种气体发生化学反应引起药品变质,影响其正常使用。因此,可以通过药瓶内部各种气体浓度的测量及时反映出药品的储存状态。其中水汽(H_(2)O)是空气中的常见气体且极易与药品产生反应,药瓶中H_(2)O浓度的测量是判断瓶内药物是否变质的重要依据之一。实际检测药瓶内水汽浓度的传统方法或通常需要直接接触到样品才能做出判断,很难做到无损检测,样品处理过程较为繁琐,耗时耗力,难以实现对大量药瓶的实时无损测量,所以需要一个实时快速非接触式检测容器密封性的方法。为了高效检测并实时监控密封药品存储容器(药瓶)内的水汽浓度,提出了一种可调谐半导体激光吸收光谱(TDLAS)的数字正交锁相解调算法,并对该算法的可行性及有效性进行了实验验证。药瓶采用长12 cm宽9 cm高64 cm的可透光聚乙烯(PE)材质;中心波长为1391 nm的分布式反馈(DFB)激光器作为光源,搭建了基于数字正交锁相解调算法的TDLAS药品检漏测量系统,以数字锁相解调代替了传统的锁相解调并且研究了不同的调制深度、采样率对解调出的二次谐波信号(WMS-2f)幅值的影响。在系统各项参数最优的情况下考察了不同光功率下WMS-2f信号稳定性,并通过拟合结果推演出其他未知水汽浓度的WMS-2f信号。研究结果表明:与常规锁相放大器解调算法相比,数字锁相解调可编译性强,系统结构更为紧凑,成本更为低廉。Allan方差分析显示在160 s内的状态下,水汽检出限为18 ppm,验证了该方法的稳定性与可靠性。

In storing drugs in sealed vials,the gas tightness of the vials often deteriorates due to improper storage methods and substandard product quality,which can easily lead to chemical reactions with various gases in the air and cause deterioration of the drugs and affect their normal use.Therefore,the storage status of drugs can be reflected by measuring the concentration of various gases inside the vials.Among them,water vapor(H_(2)O)is a common gas in the air and is very easy to react with drugs,so the measurement of H_(2)O concentration in medicine bottles is one of the important bases to determine whether the drugs inside the bottles deteriorate.In practice,traditional methods or instruments usually require direct contact with the sample to make a judgment.It is difficult to achieve nondestructive testing,and the sample handling process is tedious,time-consuming and labor-intensive,making it difficult to achieve real-time nondestructive measurement of a large number of drug bottles.In order to efficiently detect and monitor the water vapor concentration in sealed drug storage containers(vials)in real-time,a digital orthogonal phase-locked demodulation algorithm for tunable semiconductor laser absorption spectroscopy(TDLAS)is proposed in this paper,and the feasibility and effectiveness of the algorithm are experimentally verified.The drug bottle is made of transmissive polyethylene(PE)with a length of 12 cm,a width of 9 cm and a height of 64 cm,and a distributed feedback(DFB)laser with a central wavelength of 1391 nm is used as the light source.The effects of different modulation depths and sampling rates on the amplitude of the demodulated second harmonic signal(WMS-2f)are investigated.The stability of the WMS-2f signal at different optical powers is investigated under the optimal system parameters,and the WMS-2f signal of other unknown water vapor concentrations is deduced from the fitting results.The results show that the digital phase-locked demodulation is more compliable,compact and cheaper than the conventional lock-in amplifier demodulation algorithm.The Allan ANOVA shows that the water vapor detection limit is 18 ppm in the state of 160 s,which verifies the stability and reliability of the method.