Yokogawa EJX115A - Manual (Page 65)

<4. Diagnostics>
4-18
IM 01C25T01-06EN
Combination of threshold for sensitivity parameter
High Medium Low
Lim fDPmax 1.50 3.00 3.00
Lim fDPmin 0.40 0.30 0.20
Lim fSPlmax 5.00 5.00 5.00
Lim fSPlmin 0.50 0.50 0.30
Lim fSPhmax 5.00 5.00 5.00
Lim fSPhmin 0.50 0.50 0.30
Lim BlkFmax 0.60 0.60 0.80
Lim BlkFmin -0.60 -0.60 -0.80
 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 (seconds).
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.
• Procedure to call up the threshold display
DD and DTM
(excluding EJX_
HART 5[1.2])
[Root Menu] → Diag/Service
→ Diag Parameters → ILBD
parameters → Configuration →
Diag Lim →
EJX_HART 5[1.2]
DTM
Diag and Service → Advanced
Diag Configuration → Impulse Line
Blockage Detection → Threshold →
 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
• Procedure to call up the display
DD and DTM
(excluding EJX_
HART 5[1.2])
[Root Menu] → Diag/Service
→ Diag Parameters → ILBD
parameters → Status → Diag
Vriables → CRatio fDP/NRatio fDP
EJX_HART 5[1.2]
DTM
Diag and Service → Advanced Diag
Variables → CRatio fDP/NRatio 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.