SICK DUSTHUNTER T - Page 231

Operating Instructions FLOWSIC100
Gas Velocity Monitor
Product Description
8012513/03-2008 © SICK MAIHAK GmbH · Germany · All rights reserved 39
2.4 Calculations
2.4.1 Calculating and Calibrating the Volumetric Flow
Volumetric flow under actual conditions
Acoustic velocity monitors from the FLOWSIC100 series are usually used to determine the
volumetric flow in closed pipes and ducts. The volumetric flow Q
a.c.
through the
representative cross-sectional area A and the mean gas velocity across the cross-section v
A
(surface velocity)
is defined as:
The FLOWSIC100, however, determines the representative mean value of the flow velocity
on a sound path v (path velocity) between the two sender/receiver units. The sound path is
generally arranged across the diameter (see Section 3.1.1).
Since the mean values of the path and surface velocity are not identical (particularly in small
duct diameters), a functional, systematic correlation between the calculated path velocity
and the mean surface velocity similar to the point-based flow measurement (for example, a
pitot tube probe) was introduced.
K = Correction function
The correction factor k can be used for K with unimpeded, axial-symmetric flow profiles in
round pipes.
0.9 < k < 1
In many cases, however, an unimpeded, axial-symmetric flow profile is not guaranteed due
to the installation conditions (short inlet sections, rectangular ducts, unsymmetrical flow
profiles, and so on). For this reason, a second degree calibration function was implemented
in FLOWSIC to map the correlation between the mean path and surface velocity.
Note If the flow in a round pipeline is unimpeded and axial symmetric, Cv_1 is equal to the
correction factor k.
The coefficients in this calibration function can be determined by means of network
measurements and regression analysis (see DIN EN 13284-1). The calculated regression
coefficients must then be entered in the measuring device using the SOPAS ET operating
software (see Section 4.3.2).
The default value from the factory is Cv2 = 0, Cv1 = 1, Cv0 = 0.
Q
ac
v
A
A⋅=
v
A
Kv⋅=
k
v
A
v
-----
=
v
A
Cv2 v
2
Cv1 v Cv0+⋅+⋅=