| 摘要 |
<p>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. </p> |
