OvervÕkning av partikler i en fluidström

Apparatus for use in monitoring particles in a fluid flow comprises: a duct ( 1 ) for receiving the fluid flow; light generating means ( 6 ) adjacent the duct for transmitting light into the fluid flow via a first at least partially light-transmissive part ( 4 ) of the duct; light-responsive detection means ( 7 ) adjacent a second at least partially light-transmissive part ( 5 ) of the duct for receiving light from the light generating means which has passed through the fluid flow; processing means ( 8 ) for location remotely from said duct; and means ( 9 ) for coupling the processing means with the detection means, the processing means being adapted for processing signals therefrom to provide data relating to particles in the fluid flow.