Selection of Digital Filtering in the Escaping Ammonia Monitoring with TDLAS
ZOU De-bao1,2, CHEN Wen-liang1, 2*, DU Zhen-hui1, JIA Hao1, QI Ru-bin1, LI Hong-lian1,3, ZHEN Yang1, HOU Yan-xia1, XU Ke-xin1
1. State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, China 2. Key Laboratory of Micro-Opto-Electro-Mechanical System Technology，Tianjin University, Ministry of Education, Tianjin 300072, China 3. College of Quality & Technical Supervision, Hebei University, Baoding 071002, China
Abstract：Tunable diode laser absorption spectroscopy technology (TDLAS), with its advantages of high selectivity and accuracy, provides a reliable approach to the on-line detection of escaping ammonia. Firstly, the present paper introduces the TDLAS principle, experimental system and the analyses of system noise. Then with the concentration of 90×10-6 and 30×10-6 NH3 for example, we used TDLAS system to collect their second harmonic original spectrum with all kinds of noise interference. To improve the signal spectrum, five types of digital filtering methods were respectively used to filter the original spectrum. Finally we did the NH3 experiments of concentration gradient and the long time monitoring: NH3 experiment of 20×10-6. The analysis indicated that the averaging-wavelet filtering is validated to be more accurate than the other filtering methods in the noise reduction, which can improve the precision of the monitoring system from 10×10-6 to 1.25×10-6 and the SNR also increases by 14 times. It provides an effective pretreatment during the monitoring of escaping ammonia of extremely low concentration.
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