A mid-infrared methane detection device based on dual- channel lock-in amplifier

Abstract:

A portable dual-channel digital/analogue hybrid lock-in amplifier (LIA) is developed, and its amplitude detection error is less than 10% when the signal-to-noise ratio (SNR) is larger than −12 dB. Then, a differential mid-infrared methane (CH4) detection device is experimentally demonstrated based on a wideband incandescence wire-source and a multi-pass spherical reflector. The experiments are carried out to obtain the sensing performance of the device. With the absorption length of only ~4.8 cm, the limit of detection (LoD) is about 71.43 mg/m3, and the detection range is from 0 mg/m3 to 5.00×104 mg/m3. As the concentration gets larger than 714.30 mg/m3, the relative detection error falls into the range of −5%—+5%. Two seven-hour-measurements are done on the CH4 samples with concentrations of 1.43×103 mg/m3 and 4.29×103 mg/m3, respectively, and the results show that the maximum relative error is less than 5%. Because of the cost effective incandescence wire-source, the small-size and inexpensive dual-channel LIA, and the small-size absorption pool and reflector, the developed device shows potential applications of CH4 detection in coal mine production and environmental protection.