Ionisation detector cell for smoke particles - has screening plate to simulate smoke for test facility

摘要

An aerosol detector, partic. for use with smoke or fire sensors, has an ionisation chamber with a test device to attenuate the current. A probe head for a smoke detector has a first chamber (17) with an outer electrode (12) and an isolated inner electrode (22). The end (15) of a stopper member (32) carries a radioactive source which ionises the gas in the chamber. Communication holes (15) permit ingress of air together with smoke particles which have the effect of reducing the ion current between the two electrodes. A similar chamber (24), but without the communication holes, is provided as a reference standard. To provide a test facility, a sprung shutter member (80) is interposed between the two electrodes in the test chamber to attenuate the current and thus simulate the effect of smoke particles.