Yokogawa EJX930A - Manual (Page 162)

A8-12
IM 01C25R03-01E
 Simulation of Both-pressure-side
Blockage
1) Close the both-pressure-side valves.
2) Confirm the value of PRIMARY_VALUE is
stable. If unstable, open valve a little.
3) Set “Calculation” to DIAG_MODE so as to start
blockage detection operation.
4) Check that an alarm of “B Blocking” is
generated after the time that consists of DIAG_
PERIOD and DIAG_COUNT passed.
5) Check also the operation of the analog alert if
an analog alert is set.
6) Open the valves completely and check that
there are no alarms.
A8.2.9 Start ILBD Operation
If process condition and capability to detect a
blockage are confirmed, the ILBD operation can be
started according to the following procedure.
1) Check the value of sampling period
(DIAG_PERIOD).
2) Check the number of times that detect the
blockage consecutively in order to give an
alarm (DIAG_COUNT). The default value at the
shipment is set to 3 times.
3) Set “Calculation” status to DIAG_MODE.
If the reference value has not yet been
obtained, set “Reference” to DIAG_MODE.
After obtained the reference values, the ILBD
starts automatically. At the same time, DIAG_
MODE changes automatically from “Reference”
to “Calculation”.
A8.2.10 Tuning
When the pressure fluctuation amplitude in fluids is
not sufficiently large or an alarm is often generated
according to the process condition, tune up by
changing the threshold for the blockage detection
(DIAG_LIM) or the sampling period (DIAG_
PERIOD) to enhance the accuracy of the blockage
detection.
The ILBD operation must be stopped to tune up.
Set “Stop” to DIAG_MODE.
 Threshold Value
The figure below shows the image of tuning effect
with a monochrome bar.
FA0809.ai
0 1 3
Threshold (lower side) Threshold (upper side)
1) DIAG_LIM [2]
2) DIAG_LIM [4]
3) DIAG_LIM [6]
1) DIAG_LIM [1]
2) DIAG_LIM [3]
3) DIAG_LIM [5]
(a) The tuning image of the threshold values for
1) RATIO_FDP Sqrt
(VALUE_FDP/REFERENCE_FDP),
2) RATIO_FSPL Sqrt
(VALUE_FSPL/REFERENCE_FSPL),
3) RATIO_FSPH Sqrt
(VALUE_FSPH/REFERENCE_FSPH)
(b) The tuning image of the threshold values for
4) Sqrt (VALUE_BLKF/REFERENCE_BLKF)
0 -1 1
Threshold (lower side) Threshold (upper side)
4) DIAG_LIM [8] 4) DIAG_LIM [7]
Figure A8.7 Tuning Image of Threshold Value
 Move the threshold toward the white.
• It becomes increasingly likely to give an alarm
due to the disturbance from environment
change.
• If flow/differential pressure is below DIAG_LIM
[10] or exceeds DIAG_LIM [9], pressure
fluctuation is likely too small or too large to
detect the blockage.
 Move the threshold toward the black.
• It enables to be insusceptible to disturbance
such as environment change and to detect the
blockage easier.
• It becomes giving an alarm of the blockage after
the blockage has been progressed.