| 摘要 |
A suspended particle detector includes a housing (1,2) containing a radiation source (3) which shines radiation across the interior of the housing (1,2), a first radiation sensor (5) arranged to receive radiation scattered from the wall (1) of the housing (1,2) and radiation scattered from particles suspended in the housing (1,2) and to produce a first signal indicative of the total intensity of radiation incident on it. A second sensor (4) is arranged to produce a second signal indicative of the intensity of the radiation source (3). The detector also includes a signal combining circuit arranged to combine the two signals in opposition to produce a composite signal and the detector is constructed so that the composite signal has a first polarity when the density of suspended particles in the housing is less than a predetermined pressure or value and the opposite polarity when the said density is greater than the threshold value. A logic unit is arranged to detect when the polarity of the composite signal reverses and then to produce an alarm signal. |
