Yokogawa EJX440A - Manual (Page 54)

<4. Diagnostics>
4-14
IM 01C25T01-01E
The default values at the factory setting are the
values of Lim fDPmax to Lim BlkFmin shown in
Figure 4.2.2.
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 Limit
parameters corresponding to the each
blockage detection.
Note: Set to “Calculation” after setting the parameter.
Limit parameter
# Parameter Threshold value
[1] Lim fDPmax Threshold to detect “A
Blocking” by using Ratio fDP
[2] Lim fDPmin Threshold to detect “B
Blocking” by using Ratio fDP
[3] Lim fSPlmax Threshold to detect “Large
Fluct L” by using Ratio fSPl
[4] Lim fSPlmin Threshold to detect “L Side
Blocking” by using Ratio fSPl
[5] Lim fSPhmax Threshold to detect “Large
Fluct H” by using Ratio fSPh
[6] Lim fSPhmin Threshold to detect “H Side
Blocking” by using Ratio fSPh
[7] Lim BlkFmax Threshold to detect “H Side
Blocking” by using BlkF
[8] Lim BlkFmin Threshold to detect “L Side
Blocking” by using BlkF
 Sampling Period
If fluctuating around the threshold value, an
alarm maybe often generated. When the above
phenomenon happens, the sampling time ( Diag
Period) can be changed so 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 (sec).
Note: Set to “Calculation” after setting the parameter.
Also, the accuracy can be improved by increasing
the number of Diag Supp Count.
 ILBD Range Setting
If flow/differential pressure is less than the default
threshold value of Lim DPAvgmin pressure
fluctuation is not large enough to detect the
blockage. To prevent the fault blockage detection,
the threshold should be changed to larger value.
(1) Set “Stop” to Diag Mode.
(2) Enter the value to Lim DPAvgmin or Lim
DPAvgmax.
Note Set to “Calculation” after setting the parameter.
 Ratio fDP Compensation
When the flow change is too large or small, an
alarm maybe often generated. When the above
case happens, the Ratio fDP can be compensated
so as to enhance the accuracy of the blockage
detection.
 Diag DPComp
When “Compensation” is selected in Diag
DPComp, Ratio fDP is compensated by following
formula and used as treatable monitoring value,
CRatio fDP.
=
CRatio fDP CRatio fDP
Ref fDP
fDP
DPAvg
Ref DPAvg
On the other hand, if the compensation is not
necessary, “Non-compensation” is selected in Diag
DPComp and Ratio fDP is used as NRatio fDP.
=
NRatio fDP
Ref fDP
fDP
4.2.2.11 Reset of Reference Value
When there are large flow change or the change of
fluid conditions, obtain the reference value again. If
flow change by a comparison of the reference value
is ±25% or more, obtain the reference value again.