7 APPLICATION INSTRUCTIONS
7.18 PID Instruction
743
7
Auto tuning
This section explains the auto tuning function of the PID operation instruction.
The auto tuning function automatically sets the proportional gain and integral time that are important constants in order to
optimize PID control. The auto tuning function can be implemented in two methods: limit cycle method and step response
method.
Limit cycle method
■Parameters set by auto tuning (limit cycle method)
• (S3)+3 (proportional gain (K
P
))
• (S3)+4 (integral time (T
I
))
• (S3)+6 (derivative time (T
D
))
■Auto tuning procedure
When tuning is completed, the the auto tuning flags (bits 4 and 6) of (S3)+1 (action setting (ACT)) are set to OFF.
No. Procedure Description
1 Set the direct action or reverse action. Set the direct action or reverse action flag (bit 0) of (S3)+1 (action setting
(ACT)).
2 Select the auto tuning method. (Limit cycle method) Set the auto tuning method (bit 6) of (S3)+1 (action setting (ACT)) to ON. (If it is
set to OFF, auto tuning is performed in Page 745 Step response method.)
3 Set the auto tuning flag to ON. Set bit 4 of (S3)+1 (action setting (ACT)) to ON.
4 Set the input filter. Set (S3)+2 (input filter constant ()).
5 Set the sampling time. Set (S3) (sampling time (T
S
)).
6 Set the maximum output value (ULV). Set the maximum output value (ULV) in (S3)+26 (upper limit of output value
(ULV)).
7 Set the minimum output value (LLV). Set the minimum output value (LLV) in (S3)+27 (lower limit of output value
(LLV)).
8 Set the threshold value (hysteresis) (SH
PV
). Set (S3)+25 (PV value threshold (hysteresis) width (SH
PV
).
9 Set the set value (SV). Set the set value (SV) in (S1) of the PID operation instruction.
10 Set the command input of the PID operation instruction to ON
to start auto tuning.
Auto tuning is performed according to the process value (PV).
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