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1. Pf = 25.4 (in. H2O/13.6) where:
2. Pf is recorded in mm Hg
3. in. H2O = sampler side pressure reading with filter in place
4. Pf = 25.4(21.75/13.6)
5. Pf = 25.4(1.5992647)
6. Pf = 40.62 mm Hg
Po/Pa is calculated next. This is done using the following equation:
7. Po/Pa = 1 - Pf/Pa
8. where: Pa = ambient barometric pressure during calibration, mm Hg.
Inserting the numbers from the worksheet:
9. Po/Pa = 1 40.62/747
10. Po/Pa = 1- .0543775
11. Po/Pa = .946
Use Po/Pa and the ambient temperature during the calibration (Ta) to locate the flow for the calibration
point in the Look Up table.
Po/Pa = .946 Ta = 22 Look up table reading = 1.178 m3/min
This reading should be between 1.02 to 1.24 m3/min (36 to 44 CFM), the acceptable operating
range. Record this in the column titled Look Up.
Calculate the percent difference using the following equation:
12. % Difference = (Look Up flow - 1.13)/1.13 * 100
13. % Difference = (1.178 - 1.13)/1.113 * 100
14. % Difference = (0.048)/1.13 * 100
15. % Difference = (0.0424778) * 100
16. % Difference = 4.24778
In this case the % Difference has to be + or - 10% of 1.13 or 40 CFM which is 1.02 to 1.24 m3/min or
36 to 44 CFM, the acceptable operating range.