the worksheet labeled Operational Flow Rate is where the side tap reading is recorded which is taken
with only a clean filter in place. With this side tap reading, Pf and Po/Pa are calculated with the same
equations listed above. This reading should be between 1.02 to 1.24 m3/min (36 to 44 CFM), the
acceptable operating range.
This completes the calibration of this sampler.
Example Problems
The following example problems use data from the attached VFC sampler calibration worksheet.
After all the sampling site information, calibrator information, and meteorological information have been
recorded on the worksheet, actual air flows need to be determined from the orifice manometer readings
taken during the calibration using the following equation:
1. Qa = 1/m[Sqrt((H2O)(Ta/Pa))-b] Where:
2. Qa = actual flow rate as indicated by the calibrator orifice, m3/min
3. “ H2O = orifice manometer reading during calibration, in. “H2O
4. Ta = ambient temperature during calibration, K ( K = 273 + C)
5. Pa = ambient barometric pressure during calibration, mm Hg
6. m = slope of Q actual orifice calibration relationship
7. b = intercept of Q actual orifice calibration relationship.
Note that the ambient temperature is needed in degrees Kelvin to satisfy the Qa equation. Also, the
barometric pressure needs to be reported in millimeters of mercury (if sea level barometric pressure is
used it must be corrected to the site elevation). In our case the two following conversions may be
8. degrees Kelvin = [5/9 (degrees Fahrenheit - 32)] + 273
9. millimeters of mercury = 25.4(inches of H2O/13.6)
Inserting the numbers from the calibration worksheet test number one we get:
10. Qa = 1/.99[Sqrt((3.2)(295/747))- (- 0.02866)]
11. Qa = 1.01[Sqrt((3.2)(.3949129)) (- 0.02866)]
12. Qa = 1.01[Sqrt(1.2637212) ( - 0.02866)]
13. Qa = 1.01[1.1241535 ( - 0.02866)]
14. Qa = 1.01[1.1528135]
15. Qa = 1.164
It is possible that your answers to the above calculations may vary. This is most likely due to different
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