Yokogawa EJX930A - Manual (Page 148)

A8-4
IM 01C25T02-01E
 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.
 H/L Side Blocking Detection
EJX differential pressure transmitter enables
to detect both-, a high-, or low-pressure-side
blockage. The blockage degree characterized
by a comparison of high-pressure side and low-
pressure-side fluctuation values, VALUE_BLKF, is
used to detect it. The value changes within a range
of –1 to +1. As VALUE_BLKF approaches +1, the
high-pressure-side blockage progresses. On the
other hand, if it approaches -1, the low-pressure-
side blockage progresses.
1
0
1
0
FA0803.ai
VALUE_BLKF
Blockage detection for
high-pressure side
Threshold
Blockage Progress
VALUE_BLKF
Blockage detection for
low-pressure side
Threshold
Blockage Progress
-1 -1
Figure A8.2 Relation between Blockage Progress
and VALUE_BLKF
The each threshold value to detect the high- or
low-pressure-side blockage is set to DIAG_LIM [7]
or [8].
 Low Side Blocking Detection
VALUE_BLKF is preferentially used to "Low Side
Blocking" detection. If VALUE_BLKF cannot
be used, RATIO_FSPL, SQRT (VALUE_FSPL
/ REFERENCE_FSPL) is used to "Low Side
Blocking" detection. REFERENCE_FSPL is
the average value of the sum of squares of low-
pressure-side static pressure fluctuations under
normal condition. As the value of RATIO_FSPL
is below the value of DIAG_LIM [4], EJX gives an
alarm of "Low Side Blocking". On the other hand, if
this value exceeds the value of DIAG_LIM [3], EJX
gives an alarm of “Large Fluctuation of Low Side”.
 High Side Blocking Detection
VALUE_BLKF is preferentially used to "High
Side Blocking" detection. If VALUE_BLKF cannot
be used, RATIO_FSPH, SQRT (VALUE_FSPH
/ REFERENCE_FSPH) is used to "High Side
Blocking" detection. REFERENCE_FSPH is the
average value of the sum of squares of high-
pressure-side static pressure fluctuations under
normal condition.
As the value of RATIO_FSPH is below the value
of DIAG_LIM [6], EJX gives an alarm of "High Side
Blocking". On the other hand, if this value exceeds
the value of DIAG_LIM [5], EJX gives an alarm of
“Large Fluctuation of High Side”.