Shortridge Instruments AIRDATA ADM-880C, Руководство по эксплуатации

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ADM-880C 07/20/09 34
NOTE: The AirFoil probe readings will be displayed with a negative sign if the hoses are connected backwards to the meter
or to the probe. The AirFoil probe lee side pressure connector should point downstream with the air flow.
FIGURE 6.2 AIRFOIL PROBE
The AirFoil probe lee side pressure port is not equivalent to the static pressure port on a pitot tube, and must not be used
to obtain static pressure readings.
6.3.1 DUCT VELOCITY USING AIRFOIL PROBE
The scribed rings on the AirFoil probe shaft are located at one inch increments from the tip orifice, and are provided to assist
in controlling the probe measurement depth during duct velocity readings. It is helpful to apply a single wrap of electrical
tape around the probe shaft at each desired depth increment to mark measurement points.
Negative air velocities may exist in some areas of a duct traverse due to turbulence or eddy currents. The AirFoil probe
tip is designed to provide equal differential pressure for velocity in either direction across the tip. Therefore, it is
recommended that the negative velocity readings be
included in the averages of the readings taken with the AirFoil probe.
6.3.2 FUME HOODS AND SAFETY CABINETS
The AirFoil probe may be used to test the downflow air pattern and average velocity in the horizontal plane at the sash
height of safety cabinets. This test is usually done at 6" centers on a 6" x 6" traverse pattern and at 8" or 10" above the work
opening threshold. This is normally 9" to 11" above the work surface pan.
Position the AirFoil probe horizontally and up against the bottom edge of the sash door. Tape markers on the AirFoil probe
and along the sash door edge at 6" centers will aid in accurate positioning of the AirFoil probe. The individual readings for
the downflow grid should be recorded to establish the uniformity, or zone velocity profile, and compliance with the standards
required. Also the average of the downflow readings may be used to calculate the downflow cfm if required. The work
opening face velocity on total exhaust cabinets may be tested in a manner similar to procedures for fume exhaust hoods.
The velocity sample grid should be a 4" square grid for 8" sash height and a 5" grid for 10" sash settings. When calculating
average velocity or total flow, the "K
v
" factor must be taken into account as discussed in Section 6.1 VELOCITY
CORRECTION FACTORS.
The exhaust filter face velocity may also be tested with the AirFoil probe to determine exhaust air flow. The cabinet
manufacturer's probe position schedule should be used as a guide. The AirFoil probe readings have been found to be
essentially the same as "hotwire" anemometer readings taken in laboratory and field condition testing of filter discharge face
velocity.
NOTE: The exhaust air flow is most accurately determined by direct air flow measurement using the FlowHood. The 1' x
4' top assembly should be positioned so as to capture all of the intake air at the work opening. This may require the use
of masking tape and materials to block off part of the opening, depending upon the size of the cabinet.
6.3.3 EXHAUST HOODS - AIRFOIL PROBE
The AirFoil probe provides single point air velocity samples and may be used to collect data for graphing face velocity
profiles at exhaust hoods.
Air flow at the extremely low velocities (50 to 150 fpm) used in chemical exhaust hoods and safety cabinets will show
significant percentage variability at any given point (slight fluctuations in velocity represent a very large percentage
fluctuation at low velocities). Readings should be repeated several times at each sampling point to obtain an average
velocity reading for that point.