Dual detector array with noise cancellation for a particle size

Abstract

In a particle detector, a stream carrying particles to be measured is passed through a laser beam. A pair of optical collection systems are arranged perpendicular to the laser beam, opposing each other. The optical collection system reflects light signals indicative of particles sensed in the sensing region to a pair of detector arrays. Each detector array has a plurality of detectors to detect the particle signals, as well as other noise. One detector from each array monitors the same sensing region. The signals from the detectors are processed through a noise cancellation circuit. The noise cancellation circuit first amplifies each detector signal through a photo-amp. Then, the signals of the detectors in one detector array are paired up with corresponding signals of detectors, spaced at least two detectors away, in the other detector array. The paired-up signals pass through differential amplifiers, which essentially cancel the light fluctuation noise. The remaining particle signals are further processed through an A/D converter to a user interface. The dual detector array is able to achieve a better than 0.10 micron sensitivity at a particle flow of 1.0 cubic foot per minute.