Shortridge Instruments Airdata ADM-870, Руководство по эксплуатации

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ADM-870 05/23/08 23
7.0 PRESSURE MEASUREMENT
7.1 DIFFERENTIAL PRESSURE
Differential pressure measurements can be made with static pressure probes, pitot tubes, or by connecting the
pneumatic tubing directly to any appropriate pressure source within the safe operating limits for the meter. The
manner in which a pitot tube is connected to the meter is critical to the type of differential pressure measurement
being made. The meter will display DIF PRES and read out in the same units for all types of differential
pressure measurements. The operator must use care to keep track of the type of differential pressure being
measured.
The positive (+) and negative (-) ports of the meter are connected as a pair to the pneumatic pressure source
for differential pressure measurements. Maximum safe pressures for differential pressure measurement are 20
psid (900% full scale) and 60 psia common mode. The length of each external pneumatic tube should not
exceed 18 feet of 3/16" ID tubing. The handle on the meter may be locked in various positions, allowing the
meter to be set upright in order to avoid kinking the pneumatic tubing.
The meter will automatically select the differential pressure mode when first turned on if the flaps plug is not
plugged in. The meter will display DIF PRES and then IN: READ. Press the READ key to obtain the pressure
measurement.
The differential pressure between two rooms, or any other two areas may be obtained by connecting the tubing
to the positive (+) port of the meter and leaving the negative (-) port open to the ambient air pressure. Place the
end of the tubing in one area and place the meter in the other. The meter will measure the pressure differential
between the two areas.
7.1.1 STATIC PRESSURE PROBES
Static pressures are measured with static pressure probes. These probes are brass colored and have a single
tubing connection in the magnetic base. Connect the tubing from the static pressure probe to the positive (+)
port on the meter. Leave the negative (-) port open to the room air. Insert the static pressure probe into a 3/8"
hole drilled into the duct until the magnet is flush with the surface of the duct. Point the tip of the static pressure
probe directly into the airstream. Press the READ key. The meter will read the differential between the pressure
within the duct and the ambient pressure on the negative port of the meter.
7.1 STATIC PRESSURE PROBE
7.1.2 PITOT TUBE "VELOCITY PRESSURES"
Velocity pressures are obtained when the pitot tube is used and the meter is set to read out in differential
pressure. The resulting reading is recorded as velocity pressure. Connect one of the tubing sections from the
positive (+) port of the meter to the total pressure connection (in line with the main shaft) on the pitot tube and
connect the negative (-) port to the static pressure connection (perpendicular to the main shaft). If the
connections are reversed, the readings will be negative. Insert the pitot tube into a 3/8" hole drilled into the side
of the duct, being careful to align the point of the pitot tube so that it is facing directly into the airstream. If the
negative (-) connection (perpendicular to the main shaft) of the pitot tube is upstream and parallel to the duct,
the point of the pitot tube should be facing directly into the airstream.
7.1.3 PITOT TUBE "STATIC PRESSURES"
Static pressures may be obtained using the pitot tube and the differential pressure mode by connecting the
positive (+) port on the meter to the static pressure connection (perpendicular to 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