An Aerosol Analyzer

Described is a simple device for measuring the total mass and total charge of a powder cloud. The instrument consists of a sensitive electrometer circuit and a metallic collection chamber. The powder is collected on a filter paper sealed between two aluminum tubes which, if their length is three times greater than their diameter, provides sufficient shielding of the charge collected on the filter paper to justify assumption of an ``Ice Pail.'' The shielding error is less than 0.5 percent. A null-reading circuit is used with a Cenco electrometer. The necessary counter voltage for the null-reading circuit is supplied by a potentiometer circuit, and a vacuum-tube voltmeter is used to measure the voltage. Because it is desired to obtain explicitly the mass and charge of a given cloud of particles rather than the ratio of charge to mass, enough mass must be collected for weighing and, in addition, the total charge measured. This is to be accomplished without disturbing appreciably the normal flow rate of powder from the aerosol generator.