Optical discriminating fire sensor

Abstract

A fire sensor system that can discriminate between a hydrocarbon fire and the effects of a penetration flash has four channels. A first channel of the system detects electromagnetic radiation in a spectral band of relatively long wavelength and a second channel detects electromagnetic radiation in a spectral band of relatively short wavelength. A third channel compares the relative intensity of the radiation detected by the first two channels and will generate a control signal if the ratio of intensities deviates substantially from unity. This third channel control signal, when generated, will be delayed by a first predetermined period of time, and then will trigger an output signal if the first two channels still detect predetermined levels of radiation. The first predetermined delay period is set to be long enough to allow a substantial amount of the radiation of a flash subside. The sensor system also has a fourth channel that monitors the intensity of the relatively long-wavelength radiation detected by the first channel. If the long-wavelength component increases beyond a predetermined value during a second predetermined time period that begins a third predetermined time period after the third channel control signal is generated, then the output signal will be triggered. The output signal, when generated, can be used to trigger an electro-mechanical suppressant release mechanism. In another form of the four channel sensor system, the third channel generates its control signal only when the difference between the intensities of the radiation detected by the first and second channels exceeds a predetermined level.