| 摘要 |
A fire or explosion detection arrangement has a housing with first and second adjacent radiation-transmitting windows. The first window includes a filter having a passband corresponding to a narrow predetermined wavelength band. A radiation sensor mounted within the housing receives radiation from a fire or explosion through the first window, the predetermined passband corresponding to a wavelength band within which a fire or explosion to be detected generates radiation. An external source generates testing radiation having wavelengths capable of passing through the second radiation transmitting window but not through the filter. This radiation is directed to the sensor. There, means (either the sensor itself or, for example, an FET which is provided to process the normal output of the sensor) responds to the level of the testing radiation and a circuit determines from this level whether the obscuration of the second window is excessive. This is used to assess whether the obscuration of the first window is above or below a predetermined level. |
