8.5 Setting PID Constants (by Performing AT)
Notice
• Perform the AT during the trial run.
• During the AT, none of the setting items can be set.
• If power failure occurs during the AT, the AT stops.
• If AT is cancelled during the process, P, I, D and ARW values revert to the values before AT
was performed.
• AT will be forced to stop if it has not been completed within 4 hours.
• Sometimes the AT process will not fluctuate if AT is performed at or near room temperature.
Therefore AT might not finish normally.
To set PID constants, perform AT.
There are 2 types of AT.
(1) Usual AT
In order to set each value of P, I, D and ARW automatically, the AT process should be made to fluctuate
to obtain an optimal value.
For DC voltage, current inputs, the AT process will fluctuate around the SV for conditions of [A], [B] and
[C] below.
One of 3 types of fluctuation below is automatically selected depending on the deviation between SV
and PV.
[A] If there is a large difference between the SV and PV as the temperature is rising
When AT bias is set to 20 , the AT process will fluctuate at the temperature 20
lower than the SV.
(1) Calculating PID constants
(2) PID constants calculated
(3) Controlled by the PID constants
set by AT.
(4) AT bias value (Factory default: 20 )
(Fig. 8.5-1)
[B] When the control is stable
The AT process will fluctuate around the SV.
(1) Calculating PID constants
(2) PID constants calculated
(3) Controlled by the PID constants
set by AT.
(Fig. 8.5-2)
(1)
(2)
(3)
(4)
AT starting point
SV
Time
Temperature
AT starting point
(1)
(2)
(3)
SV
Time
Temperature
Temperature 20
lower than the SV
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