600
35 CPU MODULE BUILT-IN ANALOG FUNCTION
35.5 Function (PID Control Via Instruction)
*1 (s3)+20 to +24 become used only if b1, b2, or b5 are set to "1" to determine the action (ACT) (s3)+1.
*2 For supported version of each setting, refer to Page 942 Added and Enhanced Functions.
Details of parameters
This chapter describes the details of parameters.
Sampling time (s3)
Set the cycle time (ms) for the PID operation. Setting range: 1 to 32767 (ms)
• In PID control and auto-tuning (Limit cycle method)
Set the sampling time longer than the operation cycle of the PLC.
• In auto-tuning (Step response method)
Set the sampling time to 1000 ms (= 1 second) or more.
■Maximum error
The maximum error of the sampling time (TS) is from "- (one operation cycle+1 ms)" to "+ (one operation cycle)."
• When the sampling time (TS) 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.
• When the sampling time (TS) is shorter than one operation cycle of the PLC
A PID operation error occurs, however when PID operation is executed, the sampling time (TS) is equal to the operation cycle
of the PLC. In such a case, use the PID instruction in a timer interrupt, and clear (s3)+7 just before executing the PID
instruction.
Operation setting (s3)+1
■Forward operation/backward operation
Set the PID control direction (forward or backward).
• During auto-tuning for the limit cycle method
It is necessary to set the PID control direction (forward or backward) for auto-tuning.
• During auto-tuning for the step response method
The PID control direction (forward or backward) is not required, as the direction is automatically set when auto-tuning is
complete.
■The following setting is required when using the timeout time after maximum ramp (b6 and b8 of the operation setting (ACT) ((s3)+1) are "0" and "1") with the
step response method.
(s3)+25 Timeout time setting value after
maximum ramp (R) detection
1 to 32767[s] It is valid when b4, b6, and b8 of the operation
setting (ACT) ((s3)+1) are "1", "0", and "1".
(s3)+26
(s3)+27
These devices are occupied for internal processing of PID operation. Do not change data.
Operation setting (s3)+1: b0 Operation
Forward
operation
(b0=OFF)
As the measured value (PV) becomes larger than the target value
(SV), the output (MV) increases.
For example, cooling is a forward operation.
Backward
operation
(b0=ON)
As the measured value (PV) becomes smaller than the target value
(SV), the output (MV) increases.
For example, heating is a backward operation.
Set item Description/Setting range Remarks
Temperature
Measured value (PV)
Time
Target value (SV)
Temperature
Measured value (PV)
Time
Target value (SV)
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