Yokogawa EJX930A - Manual (Page 149)

A8-5
IM 01C25T02-01E
 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.
A8.2.2 Combination of Reference Result
and Blockage Detection
An EJX differential pressure transmitter can detect
four modes of impulse line blockage: both-sides,
high-pressure side, low-pressure side, and/or
single-side when all the reference values are
properly measured. However, the detectable alarm
mode combination is limited when some of the
reference values are invalid. The relation between
the detectable blockage modes and reference value
results are shown in the below figure.
NOTE
• REFERENCE_FDP must be larger than the
specified level shown in Table A8.3 (refer
A8.2.6). No blockage can be detected when
VALUE_FDP is not large enough.
• The plausibility of blockage detection needs
to be confirmed by blockage simulation test.
The simulation test can be performed by
the appropriate manifold operation (refer to
A8.2.8).
[Differential pressure transmitter]
Fluctuation Parameters Simulation Test Available Blockage Detection
REFERENCE_FDP OK
REFERENCE_FSPL OK
REFERENCE_FSPH OK
REFERENCE_BLKF OK

• Test for low-pressure side
• Test for high-pressure side
• Test for both-pressure sides

• B Blocking detection
(by using RATIO_FDP)
• Low side blockage detection
(by using RATIO_FSPL)
• High side blockage detection
(by using RATIO_FSPH)
• High/Low side blockage detection
(by using VALUE_BLKF )
REFERENCE_FDP OK
REFERENCE_FSPL OK
REFERENCE_FSPH OK
REFERENCE_BLKF NG

• Test for low-pressure side
• Test for high-pressure side
• Test for both-pressure sides

• A/B Blocking detection
(by using RATIO_FDP)
• Low Side Blocking detection
(by using RATIO_FSPL)
• High Side Blocking detection
(by using RATIO_FSPH)
REFERENCE_FDP OK
REFERENCE_FSPL NG
REFERENCE_FSPH OK
REFERENCE_BLKF NG
 • Test for high-pressure side 
• A Blocking detection
(by using RATIO_FDP)
• High Side Blocking detection
(by using RATIO_FSPH)
REFERENCE_FDP OK
REFERENCE_FSPL NG
REFERENCE_FSPH NG
REFERENCE_BLKF NG
 • Test for both-pressure sides 
• B Blocking detection
(by using RATIO_FDP)
[Transmitter for gauge/absolute pressure and level measurement]
Fluctuation Parameters Simulation Test Available Blockage Detection
REFERENCE_FDP OK  • Test for high-pressure side 
• B Blocking detection
(by using RATIO_FDP)