Mitsubishi Electric MELSEC-Q/L - Page 747

7 APPLICATION INSTRUCTIONS
7.18 PID Instruction
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7
Step response method
■Parameters set by auto tuning (limit cycle method)
• (S3)+1 (action setting (ACT)) bit 0 (action direction)
• (S3)+3 (proportional gain (K
P
))
• (S3)+4 (integral time (T
I
))
• (S3)+6 (derivative time (T
D
))
■Auto tuning procedure
1. Transfer the output values for auto tuning to (D) (manipulated value (MV)).
Set the output value for auto tuning to the "maximum output allowable for the output equipment  0.5 to 1".
2. Set the parameters (S3), (S1) (set value (SV)), which are not set by auto tuning, according to the system.
If the following precautions are not observed, auto tuning may not be performed correctly.
[Setting items]
[Precautions on setting]
• Difference between the set value (SV) and process value (PV)
To perform correct auto tuning, the difference between the process value and set value must be 150 or more at the beginning
of auto tuning. If the difference is less than 150, set the SV for auto tuning.
After completion of auto tuning, set the SV back to the original value.
• Setting time of sampling time (T
S
)
Set the sampling time for auto tuning to 1s (100ms) or more.
Set it also as is sufficiently larger than the output change period.
3. Setting bit 4 of (S3)+1 (action setting (ACT)) to ON starts auto tuning.
When the rate of change from the process value at the start of auto tuning to the set value is 1/3 or more, auto tuning is
complete and bit 4 of (S3)+1 (action setting (ACT)) is set to OFF automatically.
Start auto tuning when the system is stable. If not, auto tuning may not be performed correctly.
Setting item Remark
(S1) Set value (SV) The difference from the process value (PV) is 150 or greater([Precautions on setting]).
(S3) Sampling time (T
S
) 1000 (ms) or more ([Precautions on setting])
(S3)+2 Input filter () 
(S3)+5 Derivative gain (K
D
) When the input filter is set, the derivative gain should normally be set to 0.
Others To be set as needed
Setting item Remark
(S1) Set value (SV) Set the value so that the difference from the set value at the beginning of auto tuning is 150 or more.