Eliminating the effects of refractive indices for both white smokes and black smokes in optical fire detector

Existing optical fire smoke detectors would take more time or even fail to trigger alarms of black smokes because the optical scattering efficiencies of black smokes are much lower than those of white smokes. In this paper, we design an optical fire smoke detector with consistent response to white smokes and black smokes based on dual-wavelength technology and multiple scattering signals. The proposed detector utilizes the incident lights of dual wavelengths to measure the surface area concentration and volume concentration of fire smokes respectively. The particle size distribution of the smokes can be estimated by these concentrations. The refractive indices are deduced by the third scattering signal and more observing angles are helpful to reduce the measurement errors. As a result, a 4-channel detector [140°-950 nm, 45°-950 nm, 140°-450 nm, 45°-450 nm] is developed, which can accurately measure the concentrations of both smoldering cotton (white smoke) and open fire of polyurethane (black smoke).