DeltaOHM HD31, Operating Manual

Page: 38 / 154

HD31
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V1.6
Fig. 4.5.10: positioning the Pitot tube
The error committed in the event of a misalignment is shown in the graph below:
+0.6
+0.4
+0.2
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
0 5° 10° 15° 5° 10° 15°
P
v %
E
R
R
O
R
ANGLE
Fig. 4.5.11: misalignment error of the Pitot tube
The rotation angle around its own vertical axis with respect to the flow direction (yaw) is
shown in the abscissa (x-axis), while the % error on the measurement of the Pv differential
pressure is displayed in the y-axis (ordinate). As can be seen, a difference greater than 10°
leads to an error in the measurement of the differential pressure of less than 0.5%.
4.5.6 Z
EROING AIR SPEED PROBES
With hot-wire and Pitot probes, the probe zero should be corrected before performing a meas-
urement, i.e., ensure that - under wind-free conditions – the speed and flow rate values pro-
vided by the probe are equal to zero, at a temperature close to that of the air flow to be
measured.
1. As to AP471 S1, AP471 S2 and AP471 S3 probes, slide the cylindrical shield upwards until the
window of the air speed sensor on top of the probe is completely closed. As to the AP471 S4
probe, close the probe head with the protection cylinder. As to Pitot probes, leave the two
inputs of AP473S...module open, so as they detect the same pressure.