Yokogawa EJX930A - Manual (Page 154)

A8-4
IM 01C25R03-01E
 High/Low 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”.
 Large Fluctuation Detection
When a pump or compressor starts, the large
fluctuation is generated as process condition
changes rapidly. This phenomenon affects process
fluctuation measurement, so correct blockage
detection is not performed.
If “Large fluctuation of Low Side” or “Large
fluctuation of High Side” is detected, consider
whether a blockage result is correct.
The threshold values to detect large fluctuation are
set to DIAG_LIM [3] and [5].
Since these values are enough to detect large
fluctuation, it is not almost necessary to change
them.