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PLC User's Manual - Analog Control Edition
PID Instruction (FNC 88)
M-9
3 Parameter
3.2 Details of Parameters
K
FX
3U
-4AD-PNK
-ADP
L
FX
3U
-4AD-TC
-ADP
M
PID Instruction
(FNC 88)
3.2 Details of Parameters
3.2.1 Sampling time (TS): (S3)
Setting range: 1 to 32767 [ms]
Set the cycle time (ms) for the PID operation.
• In the PID control
Set the sampling time longer than the operation cycle of the PLC.
• In the auto-tuning
Set the sampling time to 1,000 ms (= 1 second) or more.
1. Maximum error
The maximum error of the sampling time (TS) is from "-(one operation cycle + 1 ms)" to "+(one operation
cycle)."
1) When the sampling time (T
S) is a small value
Fluctuation of the maximum error described above may cause a problem.
In such a case, execute the PID instruction in the constant scan mode, or program it in a timer interrupt
routine.
2) When the sampling time (T
S) is shorter than one operation cycle of the PLC
A PID operation error (K6740) occurs, however when PID operation is executed, the sampling time (T
S) is
equal to the operation cycle of the PLC.
In such a case, use the PID instruction in a timer interrupt (I6 to I8), and clear +7 just before
executing the PID instruction.
→ For a detailed description, refer to FX
3U/FX3UC/FX3G Series Programming Manual - Basic & Applied
Instruction Edition
S
3
X000
FNC 12
MOVP
K 0 D107
FNC 88
PID
D 0 D 1 D100 D150
+7 is reset.
(When the interrupt routine is executed for the
first time,the register for internal processing is
cleared by the pulse generation command.)
S
3
I610
The PID operation is
executed.