Characteristics of an aerosol photometer while automatically controlling chamber dilution-air flow rate.
Trials were conducted to determine those factors that affect the accuracy of a direct-reading aerosol photometer when automatically controlling airflow rate within an exposure chamber to regulate airborne dust concentrations. Photometer response was affected by a shift in the aerosol size distribution caused by changes in chamber flow rate. In addition to a dilution effect, flow rate also determined the relative amount of aerosol lost to sedimentation within the chamber. Additional calculations were added to a computer control algorithm to compensate for these effects when attempting to automatically regulate flow based on a proportional-integral-derivative (PID) feedback control algorithm. A comparison between PID-controlled trials and those performed with a constant generator output rate and dilution-air flow rate demonstrated that there was no significant decrease in photometer accuracy despite the many changes in flow rate produced when using PID control. Likewise, the PID-controlled trials produced chamber aerosol concentrations within 1% of a desired level.
O'Shaughnessy
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PT
Department of Occupational and Environmental Health, University of Iowa, 100 Oakdale Campus, #180 IREH, Iowa City, IA 52242-5000, USA. patrick-oshaughnessy@uiowa.edu
Hemenway
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D000336:Aerosols; D000392:Air Movements; D000393:Air Pollutants / Q000032:analysis; D000818:Animals; D001273:Atmosphere Exposure Chambers; D001331:Automation / Q000295:instrumentation*; D005246:Feedback; D006801:Humans; D019570:Inhalation Exposure; D010783:Photometry / Q000295:instrumentation*; D015203:Reproducibility of Results
D000336:Aerosols; D000393:Air Pollutants