Averaging
9.4.9 Volume Flow Measurement
The
volume flow
in flow channels can be cal-
culated by multiplying the average flow velocity
v
and the cross-section surface. The func-
tions needed for this purpose can be accessed
via the ´User menu´ U3
Volume flow
(see on
the right); these are a flow channel with avera-
ging, the functions ´diameter´ and ´cross-secti-
on´, and a function channel for volume flow (s.
10.3.10) If the volume flow channel has not yet
been programmed or if other functions are nee-
ded, e.g. factor or length and width for rec-
tangular cross-sections, please refer to the help
menu
Volume flow
.
As unstable measured values can be easier read out when an analog display is
used, this menu, besides a small digital display, also provides a
bar chart
.
The display range of the bar chart can be set by using the functions ´
Analog
Start
´ and ´
Analog End
´ in the menu ´Special Functions´ (s. 10.4.4). The va-
lues can also be edited directly below the scale, when programming.
Volume flow
VF = average flow velocity
v
• cross section area CS:
VF =
v
. CS
. 0.36
VF = m
3
/h,
v
= m/s, CS = cm
2
For rough air volume measurements at air vents the
average flow velocity
v
can be determined by a
time-based averaging
(s. 9.4.5 a. man. 3.5.5).The
rotating vane must be applied at one end, the averaging has to be started and
it is necessary to proceed uniformly over the whole cross-sectional area and to
stop the averaging when the other end of the cross-sectional area is reached.
Alternatively, the average flow velocity can also be determined by single
net
measurements
according to VDI/VDE 2640 (s. 9.4.4 and manual 3.5.5) (e.g.
13.24 m/s).
The average velocity
v
is displayed in function:
Average value: 13.24m¡
Input of the diameter in mm (max. 2000):
Diameter: 0150 mm
Input of the cross section area CS directly in cm
2
:
CrossSection: 0175c¥
(max. 32000 cm
2
)
Display of the volume flow VF
in a function
Volume flow:
channel
in m
3
/h:
11: 834.¦¢
Output of all function values of the menu by using:
<PRINT>
For outputting and storing the number of measuring operations, the
function channel ´
n(t)
´ is provided (s. 10.3.9, 10.3.10).
ALMEMO
®
2690-8
37
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±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±
01: 11.67 mls Volocity
|¹¹¹¹¹¹¹¹¹¸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
