Patent ID: 7162057

Claim:
An apparatus for monitoring particulate material in a flowing fluid comprising: a passageway, through which fluid to be monitored is passed, at least a portion of the passageway being translucent to enable radiation to pass through that portion; a camera, which is arranged to receive such radiation and which is constructed to generate electrical signals having a multiplicity of different values respectively representative of different values of a grey scale, the signals being representative of the images received by the camera; a frame grabber connected to the camera to isolate a frame from the signals generated by the camera; a background memory connected to the frame grabber to store data indicative of the value of background signals of the images seen by the camera; subtraction means connected to the background memory and to the frame grabber to subtract the stored values of the background signals from the values of the signals of a subsequent frame isolated by the frame grabber; an image analyzer configured to receive signals of successive frames from the frame grabber after said subtraction of values by said subtraction means, so as to provide data on successive isolated frames relating to particulate material within the flowing fluid; and out-of-focus elimination means, said out-of-focus elimination means being configured to eliminate a particle image which is out of focus by checking the rate of change in the value of signals received for successive pixels from a position away from the particle to a position within a boundary of the particle image and eliminating that particle image if the rate of change of the values of the signals does not exceed a threshold value.