ADM-860C 04/14/0853
14.5 DUCT TRAVERSE COMPARISONS, INCLINED MANOMETER, MICROMANOMETER
An inclined manometer or standard micromanometer does not correct for density effects due to barometric
pressure or temperature.
The density correction necessary for duct traverse readings which are to be compared with FlowHood readings
taken with the TemProbe in place is as follows:
Where: P
b
= local barometric pressure (in Hg)
/ F = temperature of the measured airstream
If the TemProbe is not attached during the flow measurement, the FlowHood meter will assume standard 70
/ F
(or 21.1
/ C) conditions (as do the inclined manometer and the standard micromanometer). In this case, it is not
necessary to correct the duct traverse velocity for the density effect due to temperature. However, since the
FlowHood does automatically correct for the density effect of barometric pressure, the duct traverse readings
must be corrected as follows:
Where: P
b
= local barometric pressure (in Hg)
14.6 DUCT TRAVERSE USING THE AIRDATA MULTIMETER
No corrections for density are necessary when the AirData Multimeter is used for the comparison pitot tube
traverse if use of the TemProbe is consistent during both the air flow measurement using the FlowHood and the
velocity measurement using the AirData Multimeter and pitot tube. This means that, if the TemProbe is used,
it must be used for both types of measurements.
If the TemProbe is not used for either flow or velocity, it must not be used for the other type of measurement.
In this case, both sets of measurements will be calculated using standard 70
/ F (or 21.1/ C) conditions.
14.7 BACKPRESSURE COMPENSATED COMPARISON READING
Perform a multipoint pitot tube traverse of a supply duct which serves a single supply diffuser. Calculate the air
flow with careful attention to all of the factors discussed in this section. A backpressure compensated reading
on this same diffuser should be within ± 5% of the air flow calculated from this traverse.
14.8 NONBACKPRESSURE COMPENSATED COMPARISON READING
After determining the air delivery by duct traverse, measure and record the duct centerline velocity, both with and
without the FlowHood (flaps open) in place. (A reduction in the duct centerline velocity when the FlowHood is
placed over the diffuser, is caused by the flow resistance (backpressure) of the FlowHood).
A flaps open, nonbackpressure compensated FlowHood reading on this same diffuser should be within ± 3% of
FLOW
2
(calculated from the ratio of the two centerline readings).
FLOW
2
is obtained from the following calculation:
Where: F
1
= flow calculated from duct traverse
F
2
= flow in duct with FlowHood in place (flaps open)
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