ADM-870 05/23/0824
discussed under VELOCITY PRESSURES above. The resulting pressure differential is recorded as static
pressure.
7.1.4 PITOT TUBE "TOTAL PRESSURES"
Total pressure measurements may be obtained using the pitot tube and the differential pressure mode by
connecting the positive (+) port on the meter to the total pressure connection (in line with the main shaft) of the
pitot tube and leaving the negative (-) port exposed to the ambient pressure. Insert the pitot tube into the
airstream as discussed under VELOCITY PRESSURES above. The resulting differential pressure represents
total pressure.
7.2 ABSOLUTE PRESSURES
The absolute pressure function is intended mainly to provide automatic air density correction for velocity and flow
measurements. Absolute barometric pressure measurements are obtained when the negative (-) port is open
to the atmosphere and the meter is in the absolute pressure mode. The measurement range is 10-40 in Hg.
Specific absolute pressure source measurements may be obtained by connecting the pressure source directly
to both the positive (+) and negative (-) ports (in common) of the meter. Press the MODE key until ABS PRES
is displayed. The meter will then display Hg: READ (or BAR READ). Press the READ key to take a reading.
CAUTION
If an absolute pressure source is likely to be greater than 60 in Hg (30 psia), the pressure
source must be connected in common to both the positive (+) and negative (-) meter ports
simultaneously. This avoids excessive differential pressure input which will damage the
differential pressure transducer. Maximum safe pressure is 60 psia common mode and 20 psi
differential pressure.
The absolute pressure measuring accuracy should be checked regularly. Readings taken with the negative port
(-) open to the atmosphere should be within ± 2% of the actual barometric pressure to assure rated accuracy
of density corrected flow and velocity readings.
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