Lba - Omron E5EK User Manual

4.6 LBA

F LBA detection
time
F LBA detection
width
F LBA detection
example
• The LBA (Loop Break Alarm) function can be used only on standard
type controllers.
• The LBA function can be used only when assigned as an output. Also,
the LBA function does not work when a memory error or A/D con-
verter error results.
• LBA (Loop Break Alarm) is a function for judging that an error has
occurred somewhere on the control loop and 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 at maximum output.
LBA detection time
PV
• LBA judgment is carried out at each LBA detection time from the
point of maximum output. In above figure, the process value (PV) is
changing greatly at the 1st judgment timing, so LBA remains OFF.
• At the 2nd judgment timing, the process value increases as indicated
by the broken line of the process value is normal. This means that the
change width exceeds the LBA detection width, and LBA output
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 timing and the LBA output becomes ON.
LBA detection time
Heater burnout LBA=ON
4.6 LBA
LBA detection width
Output
Time
4--15