Particle monitoring system

Claim 1

A particle monitoring apparatus for sensing particles in a flowing fluid comprising: first means having a first passage for carrying air and particles, second means having a second passage for carrying air and particles, said second passage being substantially parallel to and offset from the first passage, a housing connecting the first means with the second means, said housing having a chamber in communication with the first passage and second passage and a wall facing the chamber, said wall connecting the first means with the second means and having an angled portion located in general alignment with the longitudinal axis of the first passage, said chamber having a cross sectional area larger than the cross sectional area of either the first or second passage, a particle sensor mounted on said angled portion of said wall, said sensor located in alignment with the first passage so that the particles moving from the first passage are directed toward the sensor, said sensor operable to detect particles that strike the sensor and establish electrical signals related to the number of particles that strike the sensor, said sensor comprising a piezoelectric crystal having a surface exposed to the chamber upon which the particles impinge, said crystal being mounted on the angled portion of said wall and having a shape that conforms to the general shape of the inside of the wall whereby the crystal has a minimum extension into the chamber, an electronic circuit connected to the crystal to sense said electrical signals, and an output device operatively coupled to said circuit whereby said electrical signals are transformed to readable information related to the number of particles that strike the crystal.