Yokogawa EJX930A - Manual (Page 153)

<Appendix 8. Advanced Diagnostics>
A8-3
IM 01C25R03-01E
A8.2.1 Blockage Detection
 DIAG_LIM
When the parameter based on pressure fluctuation
exceeds the preset value, EJX diagnoses an
impulse line as blockage and gives an alarm. The
threshold values are set to DIAG_LIM [1] to [10] in
the SENSOR Transducer block.
TableA8.2 shows the default values at the factory
setting, which are different according to the model.
NOTE
When ILBD is performed for the first time, use
the default value. If the pressure fluctuation
amplitude is low or a false alarm is often
generated after ILBD is performed, change the
values of DIAG_LIM according to the procedure
described in A8.2.10.
DIAG_LIM
# Parameter Threshold value
[1] fdpmax Threshold to detect “A Blocking” by
using RATIO_FDP
[2] fdpmin Threshold to detect “B Blocking” by
using RATIO_FDP
[3] fsplmax Threshold to detect “Large
Fluctuation of Low Side” by using
RATIO_FSPL
[4] fsplmin Threshold to detect “Low Side
Blocking” by using RATIO_FSPL
[5] fsphmax Threshold to detect “Large
Fluctuation of High Side” by using
RATIO_FSPH
[6] fsphmin Threshold to detect “High Side
Blocking” by using RATIO_FSPH
[7] blkfmax Threshold to detect “High Side
Blocking” by using VALUE_BLKF
[8] blkfmin Threshold to detect “Low Side
Blocking” by using VALUE_BLKF
[9] dpavgmax Threshold to detect “Outside
Diagosis Range” by using VALUE_
DPAVG and to detect “Invalid
Ref xx” by using REFERENCE_
DPAVG.
[10] dpavgmin Threshold to detect “Outside
Diagosis Range” by using VALUE_
DPAVG and to detect “Invalid
Ref xx” by using REFERENCE_
DPAVG.
Table A8.2 Default Values of DIAG_LIM
# Parameter
Multivariable transmitter
EJX910A / EJX930A
[1] fdpmax 3
[2] fdpmin 0.3
[3] fsplmax 5
[4] fsplmin 0.5
[5] fsphmax 5
[6] fsphmin 0.5
[7] blkfmax 0.6
[8] blkfmin -0.6
[9] dpavgmax *1 1
[10] dpavgmin *1 0.05
*1: It indicates the threshold value for “Outside Diagnosis
Range” (refer to A8.2.5).
 A/B Blocking Detection
“A Blocking” and “B Blocking” indicates the result
estimated from blockage degree based on the
difference of the high- and low-pressure-side
fluctuation values. RATIO_FDP, SQRT (VALUE_
FDP / REFERENCE_FDP) is used to detect A/B
Blocking.
REFERENCE_FDP is the average value of the sum
of squares of differential pressure fluctuations under
normal condition. As the value of RATIO_FDP
exceeds the value of DIAG_LIM [1], EJX gives
basically an alarm of “A Blocking”. On the other
hand, if this value is below the value of DIAG_LIM
[2], EJX gives an alarm of “B Blocking. As a high- or
low-pressure-side blockage progresses, VALUE_
FDP increases. Therefore, “A Blocking” with a
differential pressure transmitter indicates that a
single-side impulse line is plugged for a differential
pressure transmitter.
As the both-side blockages progress
simultaneously, VALUE_FDP decreases.
Therefore, “B Blocking” with a differential pressure
transmitter indicates that bothside impulse lines are
plugged.
NOTE
A single-side impulse line blockage may
generate “B blocking” under the condition where
the fluctuation amplitude is much different
between high- and low-pressure sides.
With a transmitter to measure pressure or tank
level, “B Blocking” only is detected.