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Calibration and Auditing Procedures
Sampler Calibration
The MiniVol sampler is designed to operate at a total actual flow rate of 5.0 L/min. To ensure correct fractionation of particles at the inlet, this flow rate must be maintained within ±10% of 5.0 L/min.
Accurate calibration data for each MiniVol sampler is essential for the following:
- To determine sampler flow rate set points.
- To calculate sampler flow rate during routine QC field flow checks and QA performance audits.
- To calculate total sample volume for the computation of PM10/PM2.5 mass concentrations.
Calibration of the sampler rotameter must be traceable to the U. S. National Institute of Standards and Technology (NIST) standards. A primary standard is used to calibrate a transfer standard, which in turn is used to calibrate the sampler rotameters.
Several commercially-available transfer standards can be used in calibrations. This procedure is applicable to orifice meter transfer standards, specifically, the Airmetrics MiniFlo Transfer Standard. The following are essential considerations in choosing another transfer standard for subsequent rotameter calibrations.
- The transfer standard must be traceable to NIST through the calibration procedures referenced.
- The transfer standard must be calibrated in the appropriate flow range.
- The transfer standard should not have a significant pressure drop that affects normal sampler operation.
Regardless of the transfer standard employed, a leak-free adaptive device must be used to connect the transfer standard to the sampler inlet. The MiniFlo transfer standard is designed to connect to the inlet tube of the MiniVol filter holder. Adaptors for other devices may be purchased from Airmetrics or fabricated in-house. Obviously, the corresponding outlet on the transfer standard will determine how the transfer standard will be attached.
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