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AP473
S1
…
AP473
S4
P
ITOT
T
UBE
P
ROBES FOR THE
M
EASUREMENT OF AIR VELOCITY EQUIPPED WITH
SICRAM
MODULE
The Pitot tube is an easy method to measure air velocity in hard-to-reach positions, such as air
ducts, and in applications where air velocity and temperature are very high. As no air passes
through it, the Pitot tube is particularly suitable for measurements in hostile environments.
Measuring Principle
Static pressure holes
Total pressure hole
static pressure
velocity pressure
total pressure
The pressure inside the duct is the result of three different pressures:
1) atmospheric pressure (barometric B)
2) static pressure Ps
3) dynamic pressure Pv due to the non-null velocity of the air inside the duct.
The following formula provides the air velocity: as you can see, it depends on the three pressures
and on air temperature.
(1)
⎥⎦
⎤
⎢⎣
⎡
•
+
•
•
•
=
Pv
Ps
100.000
100.000
289
T
B
1000
1.291
v
K
[T]
Pa
[Ps]
[Pv]
mbar
[B]
m/s
[v]
°
=
=
=
=
=
The Pitot tube provides the difference between the pressure available on the front mouth and the
one measured through the lateral holes, that is Pv dynamic pressure:
(Ps+Pv) – Ps = Pv
If Ps is lower than 2500 Pa (=25mbar), the term
Ps
100.000
100.000
+
can be disregarded as the error
is of approx. 1%.
