Applied Research On Composite Technology Of Photoacoustic And Light Scattering In Fire Detection For Smoke Particles And Gas

With the development of science and technology and increasing demand for social safety,fire detection technology develops continuously from initial smoke detection and heat detection to current gas detection.Photoacoustic technology is widely used in fields of trace gas detection due to its high sensitivity.Therefore apply PA technology to fire detection is very appropriate for enhancing sensitivity of system and detecting fire more early as the components generated fist in the process of fire combustion is gaseous products.The paper selects carbon monoxide as target gas for fire detection according to combustion product in fire,and combines smoke particles to make multiple detection. Wavelength of light source of photoacoustic detection is chosen in term of theory of infrared absorption of gas,and photoacoustic signal,normal mode,loss mechanism are analyzed in detail in term of theory of photoacoustic spectrum.The attenuation of PA signal picked up is arose by both CO absorption and smoke extinction because combustion product in fire is a mixture including gaseous product and smoke particle. So we combine photoacoustic technology with smoke scattering according to scattering theory of particle,and establish a model of multiple detection combined fire gases with smoke particle.According to the signal analysis of the multiple model,gas concentration and smoke concentration signal are picked up from total photoacoustic signal. Analyze harmonic mode,quality factor and other parameters of photoacoustic cell in detail in theory.Improve filtering performance of photoacoustic cell according to fundamental theory of expansion-chamber muffler,which plays an important role to attenuate noise generated by absorption of incident beam on the windows. A wavelength modulation approach not conventional mechanical modulation is used, which makes window of photoacoustic cell has the same light absorption coefficient in a range of wavelength modulation.In this case the background noise generated is very weak as absorption of window material is almost same.According to theoretical analysis and calculation in paper,a photoacoustic cell is...