Shortridge Instruments ADM-860C, Руководство по эксплуатации

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ADM-860C 04/14/08 31
The standard AirFoil probe is a straight probe. It is often difficult to position the standard probe across an
exhaust hood opening if the hood opening frame has some relief depth on the sides and at the threshold.
Special pattern AirFoil probes are available that have the end of the probe at 90 degrees to the shaft. These
probes are more easily positioned in such hood openings and are designed to fit in the AirData Multimeter
accessory kit carrying case.
6.3.4 LAMINAR FLOW WORKSTATIONS - AIRFOIL PROBE
The AirFoil probe may also be used to measure face velocities and work zone velocities for very small sample
areas. The average of several readings must be used to represent small sample areas, due to the variability
of air flow at low velocities. Readings that vary ± 50% are not unusual when taking single point velocity
readings. The more variable the readings, the more readings must be included in the average obtained at each
location. Ten readings per sample point is usually adequate.
6.4 SINGLE POINT CENTERLINE AIR VELOCITY MEASUREMENTS
It may be necessary to take single point centerline air velocity readings using the AirFoil probe or pitot tube
under certain test conditions. These conditions may include very small ductwork (minimum size is four inches)
or other situations where it is very difficult to perform a full pitot tube traverse and it is not appropriate to use the
FlowHood.
Position the pitot tube or AirFoil probe carefully in the center of the duct. Take five or more velocity readings
and determine the average of the readings. Multiply the average of the readings by a factor of 0.9 to calculate
the approximate average velocity for the duct.
6.5 VELGRID AIR VELOCITY
IMPORTANT: See Section 6.1 VELOCITY CORRECTION FACTORS
The VelGrid accessory is designed especially for use in the measurement of general "face velocity" conditions,
such as HEPA clean room filter outlets; laminar flow work benches; exhaust hoods; terminal air face velocities;
and large filter bank and coil face velocity measurements. The measurement range using the VelGrid is 25 to
2500 fpm. Each reading represents 16 velocity points over a 14" x 14" area (1.36 sq ft).
The VelGrid unit is assembled by attaching the pushbutton handle to one of the captive knob screws of the
handle bracket, and attaching one or more of the extension rods to the other end of the handle bracket as
shown in Figure 6.3. The VelGrid swivel bracket is attached to the extension rod end. The two hoses are
connected to the VelGrid hose connectors and to the ports on the meter. The pushbutton handle cord plugs
into the external read jack on the left side of the meter. A neckstrap is provided with the VelGrid to support the
meter and allow hands free operation. The TemProbe must also be used as discussed if full density correction
for temperature is required. If the TemProbe is not used, the velocity will be calculated using the standard
temperature of 70
/ F or 21.1 / C.
After turning the meter on, press the MODE key until VelGrid is displayed, followed by FP: READ. Press the
READ key to initiate the actual measurement. (Press the STORE key if the memory function is desired).
STORE RDY will be displayed. Place the VelGrid directly on the face of the filter or coil, with the standoff
spacers of the grid against the outlet or inlet face. When placing the VelGrid near the edges of the filter, grille,
coil face, or other opening, the perimeter standoff spacers should be at least 1.5" from the edge of the
active
face area. This 1.5" margin maintains the proper "traverse" spacing of the velocity sample points at 3.5" centers
on a 14" x 14" area.
Overlapping of reading positions is better than getting too close to the face area edges. If the dimensions of
the outlet are smaller than the VelGrid, the orifices of the grid that are not directly exposed to the air flow must
be covered with tape. All unused orifice positions on
both sides of the grid manifold must be covered. Note:
The VelGrid temperature exposure limit is 0 / F to 140 / F.
The VelGrid is bidirectional in function. A negative sign will be displayed if the hose connections are reversed
or if the air flow direction is reversed in relation to the higher pressure side of the VelGrid. If the user knows that
the hoses are reversed, the negative sign may be disregarded.