Highly sensitive detection of methane based on tunable diode laser absorption spectrum

Traditional methane detection techniques in power transformer oil have the problems of cross sensitivity and insecurity factor. Based on Beer-Lambert spectral absorption law, low concentration methane detection with tunable diode laser absorption spectrum is proposed in this paper for the advantages of high sensitivity and resolution. Firstly, the central wavelength of 1653.72 nm in near infrared spectrum is selected. Then long optical length gas cell by means of refraction and reflection more than 20 times is built in the laboratory. At last, at different concentrations ranging from 50~1000 μL/L, the harmonic signal waveforms are obtained. Experimental results show that the lower detection limit of this developed methane system can detect 1.28 μL/L approximately and the deviation is less than 0.02 V, which proved to be a prospective sensing technique to be utilized in power transformers.