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A methane detection system based on tunable diode laser absorption spectroscopy (TDLAS) using LabVIEW platform was demonstrated. To suppress the noise interference in the system, a wavelet denoising method was studied and experiments with different parameters were carried out. With the threshold of Hard, the wavelet basis of Coif5 and the rule of Heursure, high frequency noises of the sensor can be effectively decreased with the harmonic amplitude increased. Experiments showed that, the 1σ minimum detection limit (MDL) was 23.68 ppbv (part per billion of volume) with an integration time of 300 s.

In order to improve the performance of the large divergence angle mid-infrared source in gas sensing, this paper aims at developing a methane (CH4) sensor with non-dispersive infrared (NDIR) technology using a compact pentahedron gas-cell. A paraboloid concentrator, two biconvex lenses and five planar mirrors were used to set up the pentahedron structure. The gas cell is endowed with a 170 mm optical path length with a volume of 19.8 mL. The mathematical model of the cross-section and the three-dimension spiral structure of the pentahedron gas-cell were established. The gas-cell was integrated with a mid-infrared light source and a detector as the optical part of the sensor. Concerning the electrical part, a STM32F429 was employed as a microcontroller to generate the driving signal for the IR source, and the signal from the detector was sampled by an analog-to-digital converter. A static volumetric method was employed for the experimental setup, and 20 different concentration CH4 samples were prepared to study the sensor’s evaluation, which revealed a 1σ detection limit of 2.96 parts-per-million (ppm) with a 43 s averaging time.

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