Azbil C1M - Page 87

5-29
Chapter 5. Functions
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Operation while AT is running
During AT, PID constants are calculated using limit cycles.
(1) A limit cycle operation is performed using the MV switching point specified
by “Type of MV switching point at AT”
During AT, two values are output repeatedly. One of the values is “MV low
limit” (OL-1 to 8) or “MV low limit at AT”(At.OL), whichever is greater, and
the other is “MV high limit” (OH-1 to 8) or “MV high limit at AT” (At.OH),
whichever is smaller.
(2) When the limit cycle has stabilized, the PID constants are changed, and AT
ends.
If C26 (heat/cool control ) is set to 1 (use (individual PID)), AT is executed using
both heating and cooling MVs.
In the first half, the MV changes to its low and high limits. In the second half, it
changes within a relatively narrow range.
If C26 (heat/cool control ) is set to 2 (use (shared PID)), AT is executed using only
heating MV.
The figures below illustrates AT with the following settings:
C26 (heat/cool control ) = 1 (use (individual PID), heating/cooling control dead
zone = 0.0 %, MV low limit = 0.0 %, MV high limit = 100.0 %
MV (%)
100.0
Time
50.0
0.0
Heating MV (%)
100.0
Time
50.0
0.0
Cooling MV (%)
100.0
Time
50.0
0.0
PV
Time
SP
Switching
point
AT in progress