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FX2N-2LC Temperature Control Block
7.2.31
BFM #49 (CH1) and BFM #68 (CH2): Loop breaking alarm judgement time
In BFM #49, set the loop breaking alarm judgement time of CH1. In BFM #68, set the loop
breaking alarm judgement time of CH2.
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.
The allowable set range is from 0 to 7,200 sec.
When BFM #49/#68 is set to "0", the loop breaking alarm function is disabled.
Abnormality judgment criteria
Table 7.5: 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 7.6: 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
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 breaking
change criteria (2 °C) within loop breaking set time, an alarm is issued.
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 breaking
change criteria (2 °C) within loop breaking set time, an alarm is issued.
Buffer Memory (BFM) 7
7-20
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