Calibration vs. Setting & Verifying Flow Rates in Air Sampling

By: Aaron Apostolico, CIH, CSP, CIEC, Contributor

A traceable electronic flow meter setting the flow rate of a personal air sampling pump. (photo courtesy of Sensidyne, LP)

Air sampling is a critical process utilized in industries such as environmental monitoring, industrial hygiene and public health. It involves measuring the concentration of airborne contaminants to inform decisions about worker safety and public health. In this article, we will discuss the difference between the term “calibration” and the process of setting and verifying flow rates in air sampling, and why it is important to follow best practices to ensure accurate and reliable results.

Calibration of Electronic Flow Meters

Pump calibration is a term that is frequently misused in air sampling. Calibration generally refers to the adjustment or verification of the accuracy and precision of a measuring instrument to an established standard, such as NIST. Electronic flow meters are utilized in air sampling to set and verify the flow rate of a sampling pump. These flow meter devices should be calibrated to established, traceable standards for volume and time.

The calibration of an electronic flow meter is done using equipment with higher accuracy that has been demonstrated to be traceable to national or international meteorological standards.

Accredited organizations certified under ISO/IEC 17011 are responsible for performing traceable calibration of equipment according to ISO/IEC 17025.

A calibration laboratory accredited to ISO 17025 standards. (photo courtesy of Sensidyne, LP)

Setting and Verifying Flow Rates

Despite being often referred to as calibration, using an electronic flow meter to set and verify the flow of a sample pump is not the same as calibrating the pump itself. Setting the pump’s flow rate is achieved by adjusting the speed of a motor, which in turn adjusts the rate at which a volume of air is delivered. Once the motor speed is adjusted, the measured flow rate on the electronic flow meter is compared with the desired or expected flow rate of the pump, and any necessary adjustments are made to the pump’s motor speed to align it with the desired flow rate.

This process is crucial to ensure that air samples are collected at the desired flow rate, along with the necessary precision (e.g., +/-5%), and should be performed each time prior to air sample collection. Without following these best practices, errors can occur, and results can be inaccurate. Users should keep in mind that changing the pump to an alternate flow rate requires the pump’s values to once again be compared to that of the flow meter.

Traceable vs. Non-Traceable Flow Meters

It’s worth noting that, in older documents, flow meters with traceable calibrations have been referred to as “primary standards” and those without as “secondary standards.” However, in metrology, a primary standard and secondary standard have different definitions, so those terms should not be applied for devices used for setting and verifying flow rates.

For the purpose of calibrating an electronic flow meter, only traceable devices should be utilized, such as described in ASTM Standard D5337*.  Nevertheless, either a traceable or non-traceable device can be utilized for setting the flow rate of a pump. There are several devices without traceable calibration commonly used, such as a field rotameter. However, even the rotameter requires calibration, and such calibration should be at the same environmental conditions, in terms of temperature and ambient pressure, where the sampling will be performed.

* ASTM Standard D5337 – Standard Practice for Setting and Verifying the Flow Rate of Personal Sampling

A rotameter, without traceability, setting the flow rate of a personal air sampling pump. (photo courtesy of Sensidyne, LP)

Importance of Proper Calibration

Ensuring accurate and reliable air sampling is critical for determining exposures and the appropriate responses to be taken. The consequences of an improper pump flow rate can lead to false-positive or false-negative results, which can have a significant impact on worker safety or public health. Additionally, using improperly calibrated equipment may result in regulatory compliance issues, leading to fines, legal action and reputational harm. Therefore, it is essential to adhere to established guidelines and regulations concerning flow meter calibration and setting the flow rate on air sampling pumps.

Conclusion

In conclusion, setting and verifying pump flow rate is a critical process in air sampling that ensures the accuracy and precision of the equipment being utilized to assess exposures. By understanding the differences between the calibrations of electronic flow meters and following the best practices for setting and verifying the flow rates of sampling pumps, organizations can ensure that air samples are collected accurately—and that results are reliable.

About the Author

Aaron Apostolico is a Certified Industrial Hygienist and the Product Applications & Research Manager with Sensidyne, LP.  He is responsible for Sensidyne’s Corporate IH program and managing product applications across multiple business lines.