Research of Examination Technology of the Second-harmonic in Coal Mine Gas Detector

In view of the flaws of the former chemistry examination method, according to the principle of laser absorption spectrum technology, it proposes that using the wavelength scanning and the current tuning of the diode laser to realize the gas absorption curve second-harmonic examination. The theoretical analysis and the result of experiment indicate that: the signal which is detected by the second-harmonic relates with not only gas absorption characteristic, but also wavelength scanning parameter and current modulation parameter. Along with the amplitude of modulation signal increasing, the amplitude of second-harmonic signal also increases, and the waveform even more tends to be regular and stable. The experiment shows that it has improved the performance of signal examination, enhanced the measuring accuracy and the examination sensitivity, and enabled the stability of the second-harmonic curve to be the best.