Yokogawa EJX440A - Manual (Page 51)

<4. Diagnostics>
4-11
IM 01C25T01-01E
NOTE
The alarms of “Invalid Ref xx” and “ILBD over
range” do not link to the 4-20 mA analog signal
and Status output.
4.2.2.6 Condition Check
After the EJX differential pressure/pressure
transmitter was installed, it is necessary to confirm if
Pres is stable under the normal operating condition
or if fluctuation amplitude under the normal
operating condition is large enough to detect the
blockage.
 Stability of Primary Value
1) Observe the value change of Pres under the
normal operating condition for 10 minutes.
2) Confirm the value change is less than 10%.
If the value change is more than 10%, the error
influences pressure fluctuation value so that the
blockage detection becomes impossible. Consider
the plant operating conditions.
 Fluctuation Value
NOTE
The blockage detection may not be carried
out correctly when pressure fluctuation
amplitude especially with the pressure and level
measurement, is small.
Confirm that each value of fDP, fSPl, fSPh, and
BlkF is more than the value specified in the below
table.
Table 4.2.4 Requirements to apply ILBD
Condition
fDP 7×10 -10 or more
fSPI 1×10 -10 or more
fSPh 1×10 -10 or more
BlkF -0.5 to 0.5
 fDP is not enough.
No blockage can be detected if fDP is not larger
than the specified value.
 Only fDP is enough.
“A Blocking” or “B Blocking” can be detected
if fSPl and fSPh are not larger than specified
values.
 fDP and fSPl are enough.
“H Side Blocking” and “Large Fluct H” can not
be detected if fSPh is not larger than specified
value.
 fDP and fSPh are enough.
“L Side Blocking” and “Large Fluct L” can not
be detected if fSPl is not larger than specified
value.
 fDP, fSPl and fSPh are enough.
All alarm modes can be detected even if BlkF is
not within the specified values.
4.2.2.7 Obtain Reference Values
The pressure fluctuation values are reduced
when the impulse line is plugged. Therefore, the
reference value is required to determine the degree
of reduction.
IMPORTANT
• If the impulse line is about to be plugged at
the time when a reference value is obtained,
blockages cannot be detected accurately.
The impulse lines on both the high-pressure
and low-pressure sides need to be cleaned
before a reference value is obtained.
• All air bubbles need to be adequately purged
before a reference value is obtained.
• Reference values must be obtained under
operating condition.
NOTE
Use Device description (DD) file for parameter
setting.