Yokogawa EJX930A - Manual (Page 56)

<4. Diagnostics>
4-6
IM 01C25R02-01E
4.2.2.1 Blockage Detection
 Limit parameter
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 Limit parameter shown
in below table.
• Procedure to call up the display
DD (HART 5/7)
DTM (HART 7)
[Root Menu] → Diag/Service → Diag
Parameters → ILBD Parameters →
Configuration → Diag Lim →
DTM (HART 5) Diag and Service → Advanced Diag
Configurations → Impulse Line
Blockage Detection → Threshold
→ Sensitivity →
Table 4.2 Limit Parameter
# Parameter Threshold value
[1] Lim fDPmax Threshold to detect “A
Blocking” by using Ratio fDP
[2] Lim fDPmin Threshold to detect “B
Blocking” by using Ratio fDP
[3] Lim fSPlmax Threshold to detect “Large
Fluct L” by using Ratio fSPl
[4] Lim fSPlmin Threshold to detect “L Side
Blocking” by using Ratio fSPl
[5] Lim fSPhmax Threshold to detect “Large
Fluct H” by using Ratio fSPh
[6] Lim fSPhmin Threshold to detect “H Side
Blocking” by using Ratio fSPh
[7] Lim BlkFmax Threshold to detect “H Side
Blocking” by using BlkF
[8] Lim BlkFmin Threshold to detect “L Side
Blocking” by using BlkF
[9] Lim DPAvgmax Threshold to detect “ILDB over
range” by using DPAvg and to
detect “Invalid Ref xx” by using
Ref DPAvg
[10] Lim DPAvgmin Threshold to detect “ILDB over
range” by using DPAvg and to
detect “Invalid Ref xx” by using
Ref DPAvg
Table 4.3 shows the default values at the factory
setting.
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 Limit parameters
according to the procedure described in
subsection 4.2.2.10. Tuning
Table 4.3 Default Values of Limit Parameter
# Parameter
Multivariable Transmitter
EJX910A, EJX930A
[1] Lim fDPmax 3
[2] Lim fDPmin 0.3
[3] Lim fSPlmax 5
[4] Lim fSPlmin 0.5
[5] Lim fSPhmax 5
[6] Lim fSPhmin 0.5
[7] Lim BlkFmax 0.6
[8] Lim BlkFmin -0.6
[9]
Lim DPAvgmax
Note 1
1
[10] Lim DPAvgmin
Note 1
0.05
Note 1: It indicates the threshold value for “ILBD over range”
(refer to subsection 4.2.2.5).
 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 (fDP / Ref
fDP) is used to detect A/B blocking. Ref 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
Lim fDPmax, EJX gives basically an alarm of “A
Blocking”. On the other hand, if this value is below
the value of Lim fDPmin, EJX gives an alarm of “B
Blocking.
As a high- or low-pressure-side blockage
progresses, 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, fDP decreases.
Therefore, “B Blocking” with a differential pressure
transmitter indicates that both-side 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.