Fluke CO-220 Fluke Air Quality Measurement - Making the Number Add Up Understa - Page 1

Making the numbers add up: Understanding specifications and performance of indoor air quality test instruments Application Note Air quality test instruments must deliver accurate and verifiable performance, both to ensure precise and reliable air quality diagnosis, and to provide credible answers if results or procedures are challenged. The air quality professional's reputation depends on the quality and performance of the test tools in use, as well as on the user's understanding of instrument specifications, technologies, applications and maintenance. In this paper we examine: • Measurement issues and air quality standards. Though firm standards for indoor air quality outside the industrial setting are limited, accurate measurement is important nonetheless. • Instrument specifications. Not all specs are created equal. Definitions of instrument performance and accuracy may vary from one manufacturer to another, making it a challenge to determine which instrument delivers the required performance. • Instrument drift and calibration. Over time, test instruments can and will drift out of spec. Instrument testing and calibration, following the schedule and methods recommended by the manufacturer, are vital to ensuring the accuracy of air quality measurement. Calibration should be documented for verification. • The characteristics of test technologies. The sensor tech- nologies used to measure some air quality parameters have limited stability. Instrument performance may be affected by such factors as altitude, ambient temperature and barometric pressure unless the user takes steps to compensate. Issues in air quality measurement The measurement of indoor air quality is influenced by a variety of factors, including the characteristics air exhibits as a fluid and gas, the standards of accuracy we must meet when making measurements, the performance characteristics of air quality test instruments and the way we use and maintain those instruments. The fluid nature of air. The subtleties of air quality measurement begin with the very nature of air. Measuring air quality is not like measuring a two by four. Because it is a gas, air is compressible. Its density varies with changes in altitude, temperature and barometric pressure. Unless compensation is dialed in when instruments are set up, or compensation circuits are built into the instruments, changes in air density can affect the accuracy of some air quality measurements. Unless it carries large quantities of pollutants, air is invisible. Instruments are needed to determine the levels of chemicals or particles borne along by the air. The principal indoor air quality characteristics we measure include: • Air temperature • Humidity • Airborne particle sizes and numbers. In sensitive environments such as medical facilities, the type of particles (such as the species of mold or bacteria) is important. • Gases, such as carbon dioxide (CO2), a byproduct of respiration that can indicate the rate of fresh air exchange into an indoor space, and carbon monoxide, a poison. From the Fluke Digital Library @ www.fluke.com/library