YOKOGAWA DPharp EJXC40A, Руководство пользователя

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<7. HART Communication>
7-44
IM 01C25W05-01EN
Move the threshold toward the white.
• It becomes increasingly likely to give a
false alarm due to the disturbance from
environment change.
Move the threshold toward the black.
• Impulse line blockage detection becomes
possible with less effect from environment
change.
• Alarms occur after the blockage has
progressed to a certain degree.
• Recalling threshold parameters
Recall
parameters
[Root menu] → Diag/Service → Diag
Parameters → ILBD parameters →
configuration → Diag Lim →
Table 7.3.2 shows the factory default threshold
values.
Change the threshold according to the following
procedure while considering the effects mentioned
above.
1) Set the Diag Mode parameter to Stop.
2) Change the Diag Lim parameter values.
Limit parameter
Parameter Threshold value
Lim fDPmax Threshold for detecting “A Blocking”
using Ratio fDP
Lim fDPmin Threshold for detecting “B Blocking”
using Ratio fDP
Lim fP1max Threshold for detecting “ Large Fluct
Pres 1” using Ratio fP1
Lim fP1min Threshold for detecting “Pres 1 Side
Blocking” using Ratio fP1
Lim fP2max Threshold for detecting “ Large Fluct
Pres 2” using Ratio fP2
Lim fP2min Threshold for detecting “Pres 2 Side
Blocking” using Ratio fP2
Lim BlkFmax Threshold for detecting “Pres 1 Side
Blocking” using BlkF
Lim BlkFmin Threshold for detecting “Pres 2 Side
Blocking” using BlkF
■ Adjusting the sampling period
If the pressure fluctuation parameter value
fluctuates around the threshold, alarm will be
generated frequently. If this happens, increase the
sampling period to increase the blockage detection
accuracy.
To change the sampling period, follow the
procedure below.
1) Set the Diag Mode parameter to Stop.
2) Set the Diag Period parameter value in the
range of 20 to 65535 (seconds).
In addition, increasing the detection count, a
condition for generating alarms, with the Diag Supp
Count parameter may also increase the blockage
detection accuracy.
■ Setting the ILBD detection range
If DPAvg exceeds DPAvgmax or falls below
DPAvgmin, the transmitter generates an “ILBD over
Range” alarm.
If flow/differential pressure is less than the default
threshold value of Lim DPAvgmin, pressure
fluctuation is not large enough to detect the
blockage. This may cause erroneous alarms that
have nothing to do with blockage.
To prevent such errors, change the threshold to a
larger value.
1) Set the Diag Mode parameter to Stop.
2) Change Lim DPAvgmin or Lim DPAvgmax.
• Recalling the threshold (Lim DPAvgmin/Lim
DPAvgmax)
Recall
parameters
[Root menu] → Diag/Service → Diag
Parameters → ILBD parameters →
Configuration → Diag Lim →
■ Ratio fDP compensation
When the flow change is too large or small, alarms
that have nothing to do with blockage may be
generated. In such a case, pressure fluctuation
parameter Ratio fDP can be compensated to
suppress such alarms.
If the Diag DPComp parameter is set to
Compensation, pressure fluctuation parameter
CRatio fDP based on the following formula can be
used in place of Ratio fDP to monitor the value.
CRatio fDP = fDP / Ref fDP × Ref DPAvg / DPAvg
If compensation is not necessary, set the Diag
DPComp parameter to Non-compensation. In
this case, Ratio fDP is treated as NRatio fDP for
monitoring purposes.
• Recalling the differential pressure fluctuation
parameter (CRatio fDP/NRatio fDP)
Recall
parameters
[Root menu] → Diag/Service → Diag
Parameters → ILBD parameters →
Status → Diag Vriables → CRatio fDP/
NRatio fDP