Patent ID: 6369890
Filing Date: 2002-04-09
Classification: G01N

Abstract:
A particle detecting apparatus for detecting the presence of particles in a gaseous fluid, comprisinga measuring chamber for receiving the gaseous fluid and defined by wall means, light sensing means having a field of view extending in the chamber, means for defining a sampling volume in the chamber, means for defining a light path in the chamber and which intersects the sampling volume, at least one pair of light emitters mounted to direct emitted light across the chamber in opposite directions along the light path towards the sampling volume, whereby particles carried by the gaseous fluid into the sampling volume scatter some of the light therein for detection by the light sensing means, the light emitters of the pair normally simultaneously emitting light and at least one thereof having a selectable light detecting mode, and control means operative intermittently to switch said one of the light emitters into the light detecting mode so that said one light emitter when switched into the light detecting mode responds to light directly received from the other emitter of the pair along the light path and produces a corresponding output which is dependent on contamination in the light path.