Shortridge Instruments Airdata ADM-870, Руководство по эксплуатации

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ADM-870 05/23/08 34
11.0 FLOWHOOD OPERATING PROCEDURE
The meter handle should be removed from the AirData Multimeter by unscrewing the captive fasteners on the
sides. The meter is inserted into the recess in the FlowHood base, using the captive fastener inside the base
to secure it. The two pneumatic tubes from the flow sensing grid attach to the pneumatic inlets on the meter.
The tube from the top side of the grid connects to the positive (+) pneumatic inlet on the meter; it is very
important that these connections are not reversed, since this will cause invalid flow measurements. The flaps
plug inserts into the flaps jack on the back of the meter.
The thumbswitch plug connected to the handgrip is inserted into the external read jack on the left side of the
meter. The TemProbe sensor is plugged into the temperature input jack on the back of the meter through the
cutout designed into the FlowHood base.
CAUTION
Avoid possible damage by removing all three electrical connections and both pneumatic connections before
removing the meter from the FlowHood base.
After being turned on, the meter will flash a full set of eights to test the display, and then pass through a brief
CAL phase. The display will then read FLO-HOOD, followed by CF: READ. After the operator presses the
READ key, either CF: UNCORR or CF: CORR will be displayed during the measurement period. CALC will
be displayed during the brief calculation period, followed by the results. Each subsequent measurement is
triggered by pressing the READ key. Pressing the READ key also clears all previous data from the registers
and the display. The meter will automatically turn off if not used for eight consecutive minutes unless readings
are stored in memory.
Place the FlowHood over the outlet (or inlet) diffuser or grille, so as to capture and direct the air flow through
the FlowHood base. The foam gasket around the edge of the top assembly should be firmly pressed against
the ceiling or the edges of the diffuser. Air flow through the unit should not be blocked or influenced by any
object within one foot of the FlowHood base. The unit should be supported with both hands, one on the handle,
and the other at any convenient point on the outside of the base. Set the flaps control knob to the open
position.
Press the READ key or the thumbswitch on the FlowHood handle and the reading will be displayed directly in
cfm or litres/sec. A negative number indicates that the air flow is being exhausted through a return outlet (or
that the hoses are crossed). A second reading with the flaps closed will be necessary to determine the
backpressure compensated air flow.
SAFETY NOTICE
When using the FlowHood to test air flow at ceiling outlets, be sure that you can safely raise and support the
unit throughout the measurement. This is especially important when working on a ladder.
11.1 AIR FLOW - NONBACKPRESSURE COMPENSATED READINGS
See Section 9.2 BACKPRESSURE COMPENSATION for a general discussion of backpressure and its effect
on any capture hood device before using the FlowHood for nonbackpressure compensated readings.
This technique measures air flow without compensating for FlowHood induced backpressure. This method is
used for both supply and return outlets.
After the meter and all of its connections have been attached to the FlowHood, as described previously, set
the flaps control knob to the open position. Place the FlowHood over the outlet (or inlet) diffuser or grille. Wait
two or three seconds to allow the air flow to stabilize, and then press the READ key or the thumbswitch on the
FlowHood handle. The displayed result will represent the flow value of the outlet while the FlowHood is in
place. This flow reading will generally be somewhat less than the actual flow, due to the backpressure effect
of the FlowHood.
Readings as low as 23 cfm may be taken with the flaps open. Readings as low as 17 cfm may be taken with
the flaps closed (see section 12.5 LINEAR SLOT DIFFUSERS). The meter will not permit nonbackpressure
compensated readings of more than 500 cfm if the flaps are closed. The flaps must be opened to continue.
11.2 AIR FLOW - BACKPRESSURE COMPENSATED READINGS
Air flow through an outlet (or inlet) is reduced to some degree by any capture hood device placed over the
opening. Correction curves had traditionally been used to provide an average correction factor for the
backpressure effects at different air flows. This method measures air flow with compensation for the FlowHood
induced backpressure automatically calculated into the displayed result.