Omron E5EK, User Manual

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CHAPTER 4 APPLIED OPERATION
E5EK
4--26
4.10 LBA
•
The LBA (Loop Break Alarm) function can be used only on standard
type controllers.
•
The LBA function can be used only when it is assigned as an output.
Also, the LBA function does not work when a memory error or A/D
converter error results.
•
LBA (Loop Break Alarm) is a function for judging that an error has
occurred somewhere on the control loop and for outputting an alarm
when the process value does not change with the manipulated vari-
able at a maximum or minimum state. Accordingly, the LBA function
can be used as a means for detecting a malfunctioning control loop.
•
Normally, when output is set to maximum or minimum, the process
value rises or falls after the dead time has elapsed. LBA is output if
the process value does not change in the predicted direction after a
fixed amount of time has elapsed. This fixed amount of time is the
“LBA detection time.”
•
LBA operation sometimes becomes unstable when the process value
fluctuates considerably due to the control characteristics. The LBA
detection width is provided so that changes with respect to output can
be correctly detected. Changes smaller than the detection width due
to LBA detection timing are not regarded as changes.
•
The following example describes what happens when a heater burn-
out occurs at maximum output.
PV
LBA=ON
LBA detection time
LBA detection width
Output
Time
Heater burnout
LBA detection time
•
LBA judgment is carried out at each LBA detection time from the
point of maximum output. In the above figure, the process value (PV)
is changing greatly at the 1st judgment time band, so LBA remains
OFF.
•
At the 2nd judgment time band, the process value increases as indi-
cated by the broken line if the process value is normal. This means
that the change width exceeds the LBA detection width, and LBA out-
put remains OFF.
•
If the heater burns out at the point shown in the above figure, the
process value “decreases.” Accordingly, it is judged that “the process
value is not changing in the increasing direction” at the 2nd judg-
ment time band and the LBA output becomes ON.
F
LBA detection
time
F
LBA detection
width
F
LBA detection
example