F:\MARKETING\TECHNICAL MANUALS\Air Samplers\DF Battery TECH MANUALS\DF-75 LPM SERIES.doc
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21
CORRECTIONS TO A REFERENCE TEMPERATURE
AND PRESSURE
FLOW RATES:
The differential pressure measurements of the differential flow sensor as a function of flow rate are
determined during the calibration process and stored in the system microprocessor.
The calculated flow rate value at the pressure and temperature conditions of the field flow
measurements (often referred to as actual flow) is determined and subsequently corrected to a
reference temperature and pressure condition that has been set at the factory.
One atmosphere pressure is the default reference pressure.
The equation utilized to correct the flow at field conditions to a reference T and P is as follows:
Flow (REF) =
Flow (Actual)
•
T REF
•
P ACTUAL
T ACT 29.92:
Hg (760mm Hg)
Reference temperature options that are factory settable are 0ºC, 20ºC, 70ºF and 25ºC.
Definitions of different reference T and P conditions
Classical STP
0Cº, 1 Atm
Normal T and P
20ºC, 1 Atm
Modified Normal T and P
21.1ºC (70ºF), 1 Atm
Standard Ambient T and P
25ºC, 1 Atm
TOTALIZED SAMPLE VOLUME:
Totalized sample volume values are corrected to standard temperature and pressure also. Totalized
volume is calculated by adding up the incremental volume calculations stored in the memory for the
collection period frequency. The incremental corrected volume is calculated from the formula.
V
incremental = Flow Rate (Corrected) × Time Interval
Totalized Volume n
V (Incremental) i
i = 1
