Novel Gas Concentration Measurements based on Harmonic Detection and a Broadband Light Source

Abstract

& The determination of gas concentration based on harmonic detection was studied theoretically and experimentally. The principle of second harmonic detection technology based on a broadband light source and the impact of modulation parameters on the harmonic signals were analyzed theoretically. The principles of multiple modulation were analyzed in order to improve the detection resolution. A fiber Bragg grating bonded to a carbon fiber cantilever was designed to achieve wavelength modulation. The impact of the modulation frequency and voltage amplitude on the second harmonic signals were studied experimentally. The output of the detector and the impact of the random noise were analyzed at different modulation frequencies and amplitudes. The optimum frequency and amplitude were determined to be 40 Hz and 2 V. The measurement of acetylene was carried out using this system. The results show that the gas measurement limit was 500 ppm, the stability was 3.92%, and the system sensitivity was 1 mV=ppm.