Shortridge Instruments Airdata ADM-870 - Appendix A: NIST Velocity Testing

ADM-870 05/23/0841
Where: P
b
= local barometric pressure (in Hg)
/ F = temperature of measured air stream
If the TemProbe is not attached during the flow measurement, the FlowHood meter will assume standard 70
/
F 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
electronic FlowHood automatically corrects 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 with a pitot tube 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 the flow or velocity measurement, 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 conditions.
14.7 BACKPRESSURE COMPENSATED COMPARISON READINGS
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 READINGS
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: FLOW
1
= flow calculated from duct traverse
FLOW
2
= flow in duct with FlowHood in place (flaps open)