Flame detector.

摘要

A flame detector arranged to detect flames includes a non-microphonic infra-red sensor 7 having a broad band frequency response. To maximise sensitivity to radiation from flames in the 4.3 pm solar absorption band a narrow band optical interference filter 6 is transmissive in the band 4.54 µm to 4.38 µm, the filter being chosen such that the integrated solar energy transmitted thereby is less than an alarm threshold.

A filter 9 prevents re-radiated heat from filter 6 reaching the sensor 7. A filter 10 prevents radiation of wavelengths less than 4.38 µm from reaching the filters 6 and 9 reducing heating thereof and also provides a series of filters to stop direct broad band transmission to the sensor through pin holes in the filters. A signal processor 11 detects flames by virtue of the flame flicker frequencies and includes provision for compensating for the effects of low frequency components on the amplitude of radiation produced by flames.