Acoustical particle detector and method
The capability for differentiating particles according to size is provided in an improved acoustical detection apparatus and method for detecting particulate matter in air or other gases. This is accomplished by controlling the flow of the gas through the capillary section of an acoustic sensor such that the flow conforms to a predetermined Reynolds number selected according to the particle size of interest. It has been found that acoustical sensors exhibit a threshold for particle size detection which varies with the Reynolds number of the flow of a gas through it. Thus, the detection of particles above a given size is achieved by controlling the flow parameters to yield a Reynolds number appropriate for detecting particles of such size.