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FX2N-2LC Temperature Control Block
5.6
Loop breaking alarm function (LBA)
The loop breaking alarm function starts to detect the variation of the measured value (PV), at
every loop breaking alarm judgment time when the output becomes more than 100% (or the
output limiter upper limit) or less than 0% (or the output limiter lower limit), then sets to ON the
loop breaking alarm (CH1: BFM #1 b8, CH2: BFM #2 b8) when judging that there is an abnor-
mality in the control loop.
Abnormality judgment criteria
Table 5.1: Heating control (reverse operation)
When output is less than 0% or
output limiter lower limit
When output is more than 100%
or output limiter upper limit
Table 5.2: Cooling control (normal operation)
When output is less than 0% or
output limiter lower limit
When output is more than 100%
or output limiter upper limit
Abnormality targets
1) Abnormality in control target: Heater disconnection, lack of power supply, wiring mistake,
etc.
2) Abnormality in sensor: Sensor disconnection, short-circuit, etc.
3) Abnormality in operating machine: Molten relay, wiring mistake, etc.
4) Abnormality in output circuit: Molten relay inside instrument, etc.
5) Abnormality in input circuit: No change in the measured value (PV) even after input has
changed
Note:
- When the auto tuning function is used, the LBA set time is automatically set to the inte-
gral time result multiplied by 2.
The LBA set time does not change even if the integral value changes.
- While auto tuning is performed, the loop breaking alarm function is disabled.
- If the LBA set time is too short or is not suitable to control targets, the loop breaking
alarm may repeatedly turn on and off or may not turn on.
In such a case, change the LBA set time in accordance with the situation.
- The loop breaking alarm function judges abnormalities in the control loop, but cannot
detect positions in which abnormalities occur.
Check each part of the control system in turn.
When measured value (PV) does not decrease at least by loop
breaking change criteria (2 °C) within loop breaking set time, an
alarm is issued.
When measured value (PV) does not increase at least by loop break-
ing change criteria (2 °C) within loop breaking set time, an alarm is
issued.
When measured value (PV) does not decrease at leas by loop break-
ing change criteria (2 °C) within loop breaking set time, an alarm is
issued.
When measured value (PV) does not increase at least by loop break-
ing change criteria (2 °C) within loop breaking set time, an alarm is
issued.
Introduction of Functions 5
5-9
5
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