Yokogawa EJX930A - Manual (Page 57)

<4. Diagnostics>
4-7
IM 01C25R02-01E
 H/L Blocking Detection
EJX differential pressure transmitter enables
to detect both-, a high-, or low-pressure-side
blockage. The blockage degree characterized
by a comparison of high-pressure side and low-
pressure-side fluctuation values, BlkF, is used to
detect it. The value changes within a range of –1
to +1. As BlkF approaches +1, the high-pressure-
side blockage progresses. On the other hand, if it
approaches –1, the low-pressure-side blockage
progresses.
1
0
1
0
F0404.ai
BlkF
Blockage detection for
high-pressure side
Threshold
Blockage Progress
BlkF
Blockage detection for
low-pressure side
Threshold
Blockage Progress
-1 -1
Figure 4.3 Relation between Blockage Progress
and BlkF
The each threshold value to detect the high- or low-
pressure-side blockage is set to Lim BlkFmax or
Lim BlkFmin.
 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.