39
38
Pitot tube and pressure probe
When measuring velocity with a Pitot tube, it is recommended to use the pressure probe
0638.1445 on account of its high accuracy level. The measuring range therefore extends to
approx. 40 m/s. Velocity
υ
is calculated in the instrument from the difference in pressure
³ p in the Pitot tube using the following formula:
υ [
m/s
]
= S x
200000 x ³p [hPa]
rho [g/m
3
]
To activate the conversion allocate one of the function buttons with “m/s”. To do this, a pressure
probe must be connected. When this button is pressed, the display changes from pressure to
velocity units and “hPa” is automatically allocated to the function button when the instrument is
switched on (in this way you can return to the pressure display). The volume flow display (m
3
/h)
can only be activated if there are m/s units in the display.
Pitot tube factor “S” and density “rho” can be set in the main menu under
SPECIAL
-
P
ARAMETER
(enter rho) or
SPECIAL
-
P
ITOT
-
FACTOR
(enter S).
The Pitot tube factor for testo Pitot tubes is a constant 1.00 and does not need to be changed. If
non-Testo Pitot tubes are used, ask the supplier for the Pitot tube factor and store it.
A volume flow funnel is required for calculating volume flow at a sucking opening (grid or button
tool with dual wall clearance). The funnel opening must cover the grid fully (max. 200 x 200 mm
with 0554.0400 or max. 350 x 350 mm with 0554.0410).
To measure, a volume probe (0635 1041 or 0635 9540) is placed in a hole in the funnel,
positioned in the middle and aligned. The probe is snapped into the funnel´s handle. Connect
the probe to the instrument and switch it on.
Allocate one of the 3 function buttons with the
function and press this function button to
allocate the third measurement duct with the volume flow unit (e.g. m
3
/h).
Enter 8.82 cm as the diameter for the funnels with Part nos. 0554.0400 and 0554.0410.
Press the funnel firmly on the opening when measuring. You can either accept the displayed
reading straightaway or you can calculate a timed mean if there are strong fluctuations in the
readings.
Vol.
Volume flow funnel
Velocity measurement
Averaging is called up via
and multi-point measurement is selected.
While the vane is moved over the duct cross-section, each
confirmation stores a single
value.
The number of logged single values appears at the top left of the display.
calculates the
arithmetic mean from these single values. This corresponds to the average velocity value and
the volume flow in m
3
/h.
sets up a new log.
extends the measurement series by a new “n x start” sequence.
Quit by pressing
.
Return to measurement menu by pressing
again.
Note:
Switching off volume flow calculation: Press
and leave the next window by pressing
.
Printing mean calculation
Press
button to print out the whole mean calculation
procedure (do not forget to switch on the printer).
Example:
Printout of a mean calculation with vane (incl.
volume flow)
Vol.
End
End
Continue
New
End
Start
Mean
Velocity measurement
2
26
6.
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09
9.
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:0
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0
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50
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m
m/
/s
s
2
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2
20
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45
5
m
m
3
3
/
/h
h
3
3
2
28
8.
.1
1
°
°C
C
2
26
6.
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0
1
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0:
:1
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0:
:4
48
8
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