APPARATUS FOR SENSING AIRBORNE PARTICULATE MATTER

摘要

1317362 Measuring air-borne particles electrically SUSQUEHANNA CORP 22 April 1971 [11 May 1970] 10886/71 Heading G1N Apparatus 10 for determining mass of particulate matter in the atmosphere comprises a housing 12 with inlet 14 through which air-borne particles flow and impinge on a sticky coating 20 on a quartz crystal 18 oscillating in a shear mode so that its oscillation frequency is inversely proportional to its mass which frequency is fed to a mixer 28 with a signal from a matched reference crystal 24 and the differency frequency signal 30 which is proportional to particle mass adhered on the crystal is fed to a display, recording or control device (not shown). In a preferred embodiment an inner housing 32 is rotatable by motor 34 between a position in which inlet nozzle 44 is aligned with collector plate 52 and nozzle 62 in a block 60 whilst outlet opening 46 of the inner housing is aligned with opening 50 in outer housing 12 and with jar 54. In use, the jar draws air through a baffle 64 in which it achieves the ambient temperature of the apparatus and is accelerated through the nozzle 62 so particles in excess of a predetermined size impinge on the collector 52. The smaller particles are accelerated by nozzle 44 to impinge on the sticky coating, which is of a sulfated ricinoleic acid, on the crystal 18. It is stated that the difference frequency signal 30 is converted to voltage which is differentiated to yield rate of change of mass so that for a known volumetric flow rate of air the particulate mass concentration is directly proportional to the rate change signal. For a step function frequency change the differentiated signal is a pulse of which the height represents the mass of a single particle.