Yokogawa EJX115A - Manual (Page 55)

<4. Diagnostics>
4-8
IM 01C25T01-06EN
4.2.2.2 Combination of Reference Result
and Blockage Detection
 Diag Applicable
The transmitter can detect four modes of impulse
line blockage: both-sides, high-pressure side, low-
pressure side, and/or single-side and abnormal
fluctuation when all the reference values are
properly measured. However, the detectable alarm
mode combination is limited when some of the
reference values are invalid. Available Blockage
Detection are shown in the below figure.
NOTE
• Ref fDP must be larger than the specified
level shown in Table 4.4 (refer to subsection
4.2.2.6). No blockage can be detected when
Ref fDP is not large enough.
• The plausibility of blockage detection needs
to be confirmed by blockage simulation test.
The simulation test can be performed by
the appropriate manifold operation (refer to
subsection 4.2.2.8).
 L Side Blocking Detection
BlkF is preferentially used to "L Side Blocking"
detection. If BlkF cannot be used, Ratio fSPl,
SQRT ( fSPl / Ref fSPl) is used to "L Side Blocking"
detection. Ref fSPl is the average value of the sum
of squares of low-pressure-side static pressure
fluctuations under normal condition.
As the value of
Ratio fSPl is below the value of Lim
fSPlmin, EJX gives an alarm of "L Side Blocking".
On the other hand, if this value exceeds the value of
Lim fSPlmax, EJX gives an alarm of “Large Fluct
L”.
 H Side Blocking Detection
BlkF is preferentially used to "H Side Blocking"
detection. If BlkF cannot be used, Ratio fSPh,
SQRT ( fSPh / Ref fSPh) is used to "H Side
Blocking" detection. Ref fSPh is the average value
of the sum of squares of high-pressure-side static
pressure fluctuations under normal condition.
As the value of
Ratio fSPh is below the value
of Lim fSPhmin, EJX gives an alarm of "H Side
Blocking".
On the other hand, if this value exceeds the value of
Lim fSPhmax, EJX gives an alarm of “Large Fluct
H”.
 Large Fluctuation Detection
When a pump or compressor starts, the large
fluctuation is generated as process condition
changes rapidly. This phenomenon affects process
fluctuation measurement; so correct blockage
detection is not performed.
If “Large Fluct L” or “Large Fluct H” is detected,
consider whether a blockage result is correct.
The threshold values to detect large fluctuation are
set to Lim fSPlmax and Lim fSPhmax.
Since these values are enough to detect large
fluctuation, it is not almost necessary to change
them.