Shortridge Instruments ADM-860C, Operating Instructions Manual

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ADM-860C 04/14/08 28
FIGURE 6.1 PITOT TUBE
If the hoses are connected incorrectly, the readings will show as negative air velocity and the meter will display
NEG PITOT. All passages and connections must be dry, clean, and free of leaks, sharp bends and other
obstructions.
After turning the meter on, press the MODE key until PITOT TUBE is displayed. Use the retractile cord to
connect the TemProbe to the meter. Insert the pitot tube and the TemProbe into 3/8" holes 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 of the pitot tube is exactly parallel to the duct, the point of the pitot tube should be facing
directly into the airstream. The shaft of the pitot tube is marked at one inch intervals to make it easier to control
the location of the pitot tube within the duct. Press the READ key to obtain the air velocity measurement.
The accuracy of pitot tube results depends heavily upon uniformity of air flow and completeness of the duct
traverse. Careful technique is critical to good results. Pitot tubes are available in several different sizes and
configurations to simplify different applications which may be encountered.
When a pitot tube is used in internally insulated ducts, small particles of fiberglass may be dislodged and
become caught in the openings of the tube. This will effect the accuracy of the readings and eventually clog
the tube. Remove the connections to the meter and blow compressed air through the bottom of the inside tube
to discharge fiberglass particles from the tip of the pitot tube.
NEG PITOT will be displayed if the pitot tube readings are negative. This will occur if the positive (+) and
negative (-) hoses have been incorrectly connected to the inlet ports of the meter; if the probe has been
improperly positioned in the airstream; or if the pitot tube tip has been placed in an area of flow reversal or eddy.
It is common practice, although not a purely accurate procedure, to consider negative pitot tube readings as
zero in the averages of pitot tube traverse readings. If a memory sequence has been started, a NEG PITOT
display will be stored as zero. This zero will be calculated in the velocity sum and average, and will be displayed
as a minimum reading of NP 0. It will also be recalled as nns NP 0.
A memory sequence cannot be
started with a NEG PITOT reading.