Filter
Top Products
9 PID CONTROL FUNCTION
9.6 Details of Parameters
59
9
9.6 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.
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.
Temperature
Measured value (PV)
Time
Target value (SV)
Temperature
Measured value (PV)
Time
Target value (SV)