11. Measuring with the measuring menus
11.4.9 Volume flow measurement
The
volume flow
in flow channels can be cal-
culated by multiplying the average flow velocity
and the cross-section surface.
v
The functions
needed for this purpose can be accessed via
the user menu U3
Volume flow
(see right);
these are a flow channel with averaging, the
functions “diameter” and “cross-section”, and a
function channel for volume flow (see 12.3.10).
If the volume flow channel has not yet been pro-
grammed or if other functions are needed, e.g.
profile factor or length and width for rectangular
cross-sections, you can use the wizard menu
Volume flow
.
Volume flow
VF = average flow velocity
v
• Cross-section surface CS
VF =
v
. CS
. 0.36
VF = m
3
/h,
v
= m/s, CS = cm
2
The average flow velocity
v
For rough air volume measurements at air vents
and gratings the average flow velocity can be determined by means of
time-
based averaging
(see 11.4.5 and Manual 3.5.5). You apply the rotating vane
at one end, start averaging, and proceed uniformly over the whole cross-sec-
tion; when you reach the other end of the cross-section stop averaging.
Or alternatively the average flow velocity can also be determined by means of
single array measuring operations
as per VDI/VDE 2640 (see 11.4.4 and
Manual 3.5.5) (e.g. 13.24 m/s).
To display, output and save the number of measuring operations the
function channel ´
n(t)
´ is also provided (see 12.3.9, 12.3.10).
With Pitot tubes, in order to calculate actual velocity, temperature compensation
and atmospheric pressure compensation must be provided.
The average velocity is shown by the function
v
Averagevalue: 3.24m¡
Enter the diameter in mm (maximum 2000):
Diameter : 0150 mm
Enter the cross-section surface CS directly in cm
2
:
Cross-section: 175c¥
Display the volume flow VF
in a
volume flow
function channel
in m
3
/h:
11: 834.¦¢
To output all function values of the menu press
<PRINT>
Converting to standard conditions
With all flow sensors it is possible to convert the actual measured values to
standard conditions, i.e. temperature = 20°C and atmospheric pressure = 1013
mbar. To do this ´
#N
´ must be programmed in the designation either in the
speed channel or in the volume flow channel only; this then automatically pro-
duces the standard volume flow.
46 ALMEMO
®
5690-2M
C © REC COM l© ©l R01 * ´´´´´´µµµµ¶
±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±
01: 11.67 mls Volocity
|¹¹¹¹¹¹¹¹¹¸¹¹¹¹¹¹¹¹¹¸¹¹¹¹¹¹¹¹¹¸¹¹¹¹¹¹¹¹¹¸¹¹¹¹¹¹¹¹¹|¹¹¹¹¹¹®®®¸®®®®®®®®®¸®®®®®®®®®¸®®®®®®®®®|
5.00 S220 mls 15.00
Damping:
20
Averaging mode:
CONT
Average value:
13.24 mls
Counts:
12
Volume flow:
11: 8343. m
3
/h
Diameter:
150 mm
Cross section:
175 c¥
START MANU M PRINT ESC
