Abstract
Many sampling machines are so designed that a check of the flow rate or a calibration of a fitted flow meter is straightforward. There are others, however, such as the MSA electrostatic sampler, which present serious difficulties when attempts are made to use the standard methods. The development of a simple, accurate, and rapid null-point method for determining the air flow rate is described, The apparatus required is an air mover capable of delivering a flow rate in excess of the sampler being tested, a vessel about 20 liters in capacity, and a manometer, hot-wire anemometer, or other flow-sensitive device. The method has been validated by comparison with others, based on different principles.