| 摘要 |
A first channel including filter 1 and photodetector 2 senses emission from a flame in the wavelength range below 6 mu particularly that characteristic of carbon dioxide and produces signals to be used to operate alarm means. A second channel including filter 9 and detector 10 senses spurious emission produced by other thermal radiators in the wavelength range of a long-wave spurious emission above 6 mu m. Means 17, 18 interconnects the circuits of the first and second channels in such a way that, while taking account of the statistical distribution of the flame emission and the spurious emission, an output signal is produced in such a way that the further transmission of the signal of the first circuit is blocked if a unidirectional output signal of the second circuit occurs synchronously therewith whereas it is transmitted to the alarm means if the output signal of the second circuit is non-synchronous or of opposite phase with respect to the first circuit signal, is absent or does not occur unidirectionally. The first and second channel circuits utilize flame flicker frequency filters of the same band pass range. The gate circuit 18 output is applied to an integrator 19 to avoid spurious signals actuating the alarm, and a delay line 21 to delay initiation of an alarm. Construction of the filters 1, 9 is described, Figure 8. Various types of photodetector 2, 10 may be employed. Other circuits are described, Figures 10, 11, 12. <IMAGE> |
