ADM-870 05/23/0818
and the TemProbe into 3/8" holes drilled into the side of the duct, being careful to align the AirFoil tip as
discussed above. Press the READ key to obtain the air velocity measurement. As soon as the display reads
CALC, the AirFoil probe may be moved to another position.
6.2 AIRFOIL PROBE
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 static pressure connector should point downstream with the air
flow.
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 AirFoil probe measurement depth. It is helpful to apply a single wrap of
electrical tape around the 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 - AIRFOIL
The AirFoil probe may be used to test the downflow air pattern and average velocity in the horizontal plane at
the sash height of fume hoods and 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 of the downflow grid should be recorded to establish the "evenness" 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 blank off part of the opening, depending upon the size of the
cabinet.
The AirData Multimeter default air density correction is to local air density with reference to barometric pressure.
Comparison with "hot wire" anemometer readings may require the correction of the "hot wire" readings to local
density conditions. See Section 13.5 HOT WIRE ANEMOMETER VS AIRDATA MULTIMETER. Also, see
Section 6.5 VELOCITY: LOCAL VS STANDARD DENSITY.
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