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FLOWSIC600 · Technical Information · 8010125 V 4.0 · © SICK AG
Product Description
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2.4
Path failure compensation
The measured value of the failed path is substituted with a calculated replacement value.
This replacement value is calculated on the basis of the current valid values measured for
other paths, and the relationship of gas velocities between the individual paths. The rela-
tionship between the paths for valid measurements is defined by the individual flow profile
value in the installation. This relationship is continuously calculated and saved during
undisturbed measurement operation of the meter.
Field studies have shown that it is useful to distinguish between two ranges (low velocity
and high velocity). The relationship of gas velocities between the paths is stored separately
for each of these two ranges.
Automatic determination and learning of path relationships
During normal operation, the individual path relationship P
Path
is calculated continuously.
These relationships are used in an adaptive mean value calculation routine for each
individual path. Statistical variation caused by turbulence is sufficiently suppressed with
the help of this mean value calculation. This algorithm further allows the measuring
system to adapt to different flow profiles caused by changes in operating conditions.
NOTICE:
Type approval
A 4-path FLOWSIC600 is able to compensate for the failure of one or more
paths using a static or an adaptive compensation routine as described below.
Path failure may be caused by a received ultrasonic signal which is invalid, i.e.
the quality of the ultrasonic signal received will not allow the determination of a
correct signal travel time and therefore correct gas velocity for this path.
●
A 4-path FLOWSIC600 configured for custody transfer application (custody
configuration) will indicate the compensation of one path failure with the
meter status "Check Request". If two or more paths fail, the meter status
"Data invalid" will be activated.
●
A 4-path FLOWSIC600 configured for process applications will indicate the
compensation of up to three path failures with the meter status "Check
Request". If the remaining last path fails, the meter status "Data invalid" will
be activated.
v
A:
Mean area
velocity
N:
Number of
measuring
paths
w
i
: Weighting factor
of a:
measuring path
Due to the unique path relationships of each individual installation, every
meter must determine the path relationships during the commissioning
procedure (
).
In order to ensure that the system is able to compensate for path failure at
both high and low flow velocities, it is recommended that the FLOWSIC600
meter be run for 20 minutes at low gas velocities (< 8 m/s) (< 26.25 ft/s) first
and then for 20 minutes at high gas velocities (> 8 m/s) (> 26.25 ft/s) during
commissioning.
P
Path i
=
v
Path i
v
A
1
v
A
=
w
i
·
v
Path i
N
i = 1
N
(1)
The mean area velocity is calculated as follows:
(2)
