Yokogawa EJX930A - Manual (Page 157)

<Appendix 8. Advanced Diagnostics>
A8-13
IM 01C25T02-01E
 Move the threshold toward the white.
• It becomes increasingly likely to give an alarm
due to the disturbance from environment
change.
• If flow/differential pressure is below DIAG_LIM
[10] or exceeds DIAG_LIM [9], pressure
fluctuation is likely too small or too large to
detect the blockage.
 Move the threshold toward the black.
• It enables to be insusceptible to disturbance
such as environment change and to detect the
blockage easier.
• It becomes giving an alarm of the blockage after
the blockage has been progressed.
The default values at the factory setting are the
values of DIAG_LIM [1] to [8] shown in Table A8. 2.
Change the threshold value to solve your problem
according to the above image
(1) Set “Stop” to DIAG_MODE.
(2) Change the unsuitable value of DIAG_
LIM corresponding to the each blockage
detection.
Note:Set to “Calculation” after setting the parameters.
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
A8.2.10.2 Sampling Period
If fluctuating around the threshold value, an
alarm may be often generated. When the above
phenomenon happens, the sampling time (DIAG_
PERIOD) can be changed as as to enhance the
accuracy of the blockage detection.
The longer the sampling time, better the expected
accuracy.
(1) Set “Stop” to DIAG_MODE.
(2) Enter the value to DIAG_PERIOD within
the range of 20 to 65535 (seconds).
Note: Set to “Calculation” after setting the parameters.
Also, the accuracy can be improved by increasing
the number of DIAG_COUNT.
A8.2.10.3 ILBD Range Setting
When the VALUE_DPAVG is less than the value of
the DIAG_LIM [10] or exceeds the value of DIAG_
LIM [9] shown in Table A8. 2, EJX gives an alarm of
“Outside Diagnosis Range”.
If flow/differential pressure is less than the default
threshold value of DIAG_LIM [10], pressure
fluctuation is not large enough to detect the
blockage. To prevent the fault blockage detection,
the threshold value should be changed to larger
value.
(1) Set “Stop” to DIAG_MODE.
(2) Enter the value to DIAG_LIM [10].
Note: Set to “Calculation” after setting the parameters.
A8.2.10.4 COMP_FLG
When “Compensation” is selected in COMP_FLG,
RATIO_FDP is compensated by following formula
and used as treatable monitoring value, CRATIO_
FDP.
X REFERENCE_DPAVG
CRATIO_FDP =
VALUE_DPAVG
VALUE_FDP
REFERENCE_FDP
On the other hand, if the compensation is not
necessary, “Non-compensation” is selected in
COMP_FLG and RATIO_FDP is used as NRATIO_
FDP.
= NRATIO_FDP
VALUE_FDP
REFERENCE_FDP
A8.2.11 Reset of Reference Value
When there are large flow change or the change of
fluid under the measured process conditions, obtain
the reference value again.
If flow change by a comparison of the reference
value is ±25% or more, you need to obtain the
reference value again.