CFM-88L 07/20/0912
7.0 ABSOLUTE PRESSURE
The absolute pressure function is intended mainly to provide automatic air density correction for the 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 the 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 precaution avoids excessive differential pressure input which will damage the 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.
Weather service or airport reports of barometric pressure have usually been adjusted for altitude, so the pressure can be
used for altimeter adjustment. The barometric pressure announced on television or radio stations is generally obtained from
weather service reports. This altitude corrected barometric pressure must not be used in density correction equations for
comparison with a FlowHood. An estimation of the actual barometric pressure may be obtained by deducting approximately
1.0 in Hg for each 1000 feet above sea level.
To Next Page
Loading...
Need help?
General
