Product Description
FLOWSIC100 Flare · Operating Instructions · 8013344/11L2/V 2-5/2018-10 · © SICK Engineering GmbH
69
Su
bj
ect
to
ch
an
ge
with
ou
t n
otic
e
2.3
Computations
2.3.1
Calculation and calibration of volume flow
Volume flow in operating state
Generally, the devices of the FLOWSIC100 Flare family are used to determine the volume
flow in closed pipelines. The volume flow Q
ac
is defined by the representative cross-
sectional area A and the mean gas velocity v
A
with respect to cross-section (area velocity):
FLOWSIC100 Flare, however, determines the representative average value of the flow
velocity on a sound path v (path velocity) between the two sender/receiver units. The sound
path is to be placed centrally above the cross-section of the pipeline.
Since the average values of path and area velocity are not identical, especially for small
pipe diameters, a functional, systematic relation between the determined path velocity v
and the average area velocity v
A
was introduced.
This functional relation is implemented by a calibrating function in the FLOWSIC100 Flare.
The coefficients of this function are determined at factory through comparison
measurement on a test bench and regression analysis, and stored in the MCUP control
unit. The coefficients for various nominal pipe diameters are activated during start-up.
Calculation of volume flow in the standard state
The volume flow can be converted as follows to the standard state:
Q
ac
:
Volume flow in actual state
Q
sc
:
Volume flow in standard state
p
pipe
:
Absolute pipeline pressure; usually entered as constant/default value typical
for the equipment.
If an optional analog module is used as an analog input for connection of a
separate pressure transducer, the volume flow can be normalized
with
current plant values.
p
normal
: 1013 mbar
T
pipe
:
Gas temperature (in K): In FLOWSIC100 Flare, a choice can be made here
whether to use a substitute constant temperature determined with ultrasonic
measurement or the substitute temperature read in via the optional analog
input (to increase precision).
T
normal
:
Standard temperature. In Europe 273 K, in the USA 293 K
κ
:
Compressibility (=1 for ideal gases); can be configured as a constant
The coefficients can be specified and entered into the measuring system by an
optional flow calibration, and the measuring precision thereby improved even
further.
Q
ac
= v
A
• A
k
f Re
(
)
v
A
v
Path
------------
=
=
0.9 < k < 1
(Re = Reynolds‘ number)
Q
sc
Q
ac
p
pipe
T
normal
•
p
normal
T
pipe
•
-------------------------------------
1
κ
---
•
•
=
