7.3 Using a Rotameter
Calibrating the PQ100 Air Sampler with a Rotameter is to be avoided for two reasons.
The PQ100 is more accurate (.5% of the expected flow rate) than the typical rotameter
(within 3% of Full Scale). Secondly, the rotameter, unlike the bubble meter, has a
reference condition calibration and requires a correction for ambient conditions.
The procedure for using a rotameter is best illustrated by example.
Example 4:
Referring to the conditions cited in example 1 (Appendix A), the required set point is
9.74 Lpm. If a rotameter is used, they are typically calibrated at 760 millimeters of
Mercury and 70 degrees Fahrenheit (21.11 degrees Celsius or 294.29 degrees Kelvin).
The room conditions in Example 1 were 19 degrees Celsius and 765 millimeters of
Mercury. The equation for the rotameter correction is;
PT TI 2
QI = QT ( --- x --- )
PI TT Equation #4
760 292.18 2
QI = 9.74 ( ---- x ------- ) = 9.66 Lpm
765 294.93
where;
QT is the Rotameter Calibration Condition flow rate in Liters per
minute (Lpm)
QI is the calibrator reading (Lpm) at a given Time, Temperature and
Barometric Pressure
PT is the Rotameter Calibration Condition Barometric Pressure (760)
in millimeters of mercury (mm of Hg)
PI is the Indicated Barometric Pressure reading (mm of Hg.) at the
time of the calibrator flow reading
TT is the Rotameter Calibration Condition Temperature (21.11) in
degrees Celsius.
TI is the Indicated Temperature reading (degrees Celsius) at the time
of the calibrator flow reading.
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