Fig. 1. Structure of NDIR gas sensor

Fig. 2. Measuring device of gas absorption spectra

Fig. 3. Spectra of air，sulfur hexafluoride and filter

Fig. 4. Dual-channel IR sensor with TO-packaged

Fig. 5. Transmissivity spectrum of silicon wafer

Fig. 6. Spectral curves of Ge and ZnS films

Fig. 7. Transmission spectrum of narrow band main film

Fig. 8. Transmittance spectrum of the cut-off film

Fig. 9. Spectra of the filter