Aalborg DFM Digital - Manual (Page 30)

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Figure b-20, Zero Calibration (Completed)
If the device was unable to adjust Sensor reading to within 120 ± 2 counts, then
Auto Zero is considered as unsuccessful and user will be prompted with "Auto
Zero is Failed!" screen.
5.3.11 Flow Conditions Settings
For DFM 27/37/47 models the flow reading can be displayed for standard or actu-
al conditions (Temperature / Pressure adjusted). Since mass flow sensors are sen-
sitive to changes in gas density and gas velocity, all mass flow meters indicate flow
rates with reference to a set of standard conditions. For Aalborg
7 Instruments,
standard conditions are defined as 21.1° C (70° F) and 101.3 kPa (14.7 psia).
Other manufacturers may use different values. Standard flow rate is the flow rate
the gas would be moving if the temperature and pressure were at standard condi-
tions. It is usually the most convenient measure of the gas flow because it defines
the heat-carrying capacity of the air. Actual (volumetric) flow rate is the true vol-
ume flow of the gas exiting the flow meter. In some instances, actual (volumetric)
flow rate rather than standard flow rate may be of interest. To display actual (vol-
umetric) flow rate, the DFM will multiply the standard flow measurement by the
following density correction factor:
Where:
Ta = Actual gas temperature measured by the DFM in units of degrees Celsius
Pa = Actual absolute pressure measured by the DFM in units of PSI
Note: The Actual Flow reading will not be calculated for % F.S.
engineering unit.
In order to select Standard or Actual flow measurement user would traverse the
menu tree until reaching the "Flow Conditions" menu. The following screen will
appear:
,