Abstract
A time division multiplexing differential modulation technique is proposed to address the interference problem caused by the fluctuation of laser light intensity in the single optical path detection system. Simultaneously, a multi-reflection chamber is designed and manufactured to further improve the system’s precision with an optical path length of 80 m. A near-infrared C2H2 detection system was developed. The absorption peak of the acetylene (C2H2) molecule near 1520 nm was selected as the absorption line. A laser driver is developed, and a lock-in amplifier is used to extract the second harmonic (2f) signal. A good linear relationship existed between C2H2 concentration and the 2f signal, and the correlation coefficient was 0.9997. In the detection range of 10–100 ppmv, the minimum detection limit was 0.3 ppmv, and the precision was 2%. At 50 ppmv, C2H2 and continuous detection for 10 h, the data average was 50.03 ppmv, and the fluctuation was less than ±1.2%. The Allan variance method was adopted to evaluate the long-term characteristic of the system. At 1 s of integration time, the Allan deviation was 0.3 ppmv. When the integration time reached 362 s, the Allan deviation was 0.0018 ppmv, which indicates the good stability of the detection system.
Highlights
Acetylene (C2 H2 ) is one of the most basic raw materials for industrial production
The detection system can obtain the concentration value in one stair-stepping segmented signal cycle, and 10 concentration values are displayed after average processing
A time division multiplexing differential modulation technique is proposed to eliminate the interference caused by the fluctuation of laser source in a single optical path detection system
Summary
Acetylene (C2 H2 ) is one of the most basic raw materials for industrial production. C2 H2 is burned at high temperature to weld metals. The DFB laser is driven and modulated by superimposing a high-frequency sine signal by a stair-stepping segmented low-frequency signal It can eliminate the background noise caused by the fluctuation of laser light intensity, which further improves the detection precision. The precision of the single-optical TDLAS gas detection system can be greatly improved by adopting a time division multiplexing differential modulation technique and the multi-reflection chamber method. It can better satisfy the high-precision detection requirements for C2 H2 gas in practical applications without increasing the complexity of the system. A laser driver, which uses a time division multiplexing differential modulation technique to eliminate interference caused by the fluctuation of laser light intensity in the single optical path detection system, is developed. 2f/1f normalization [16,17]
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