Bubble meter, calibration method

Calibrate personal sampling pumps before and after each day of sampling, using either the electronic bubble meter method or the precision rotameter method (that has been calibrated against a bubble meter). 

Flow meters on field sampling instruments are calibrated using one of several methods. Primary standards are tliose which measure volume directly and are, therefore, preferred. Primary air flow standards include bubble meters, spirometers and Mariotti botdes. The time required to draw a measured volume of air through these systems is measured and the resulting flow rate is calculated. These methods are typically accurate to within one percent. 

Assemble the polystyrene cassette filter holder using the appropriate filter for the sampling method. If a cassette adapter is used, care should be taken to ensure that it does not come in contact with the back-up pad. When calibrating with a bubble meter, the use of cassette adapters can cause moderate to severe pressure drop in the sampling train, which will affect the calibration result. If adapters arc used for sampling, then they should be used when calibrating. 

Different methods used for calibrating samplers include rotometers, wet-test meters, pressure gauges across fixed orifices, mass flow meters, hot wire flow meters and bubble tubes. Each of these calibration devices requires an appropriate correction factor. Some of the devices measure mass flow rather than volumetric flow. Sampling requires volumetric flow calibration. 

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