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S. AT1
(11) PID constant calculation processing
The response speed (R), equivalent dead time (L) and AT1 stepped manipulated value (AT1STEPMV) are assigned to
the adjustment rule to calculate the PID constants.
(a) Control system
The control system is selected according to the integral constant TI (I) and derivative constant TD (D).
Integral constant TI (I)
Derivative constant TD (D)
TI  0
––
TI > 0
Control method
Proportional control (P operation) only
TD  0
PI control (PI operation)
TD > 0
PID control (PID operation)
(b) Adjustment rule
The ZN process: adjustment rule based on the stepped response of Ziegler and Nichols is used.
Control
Rate example gain Kp (P)
method
Integral constant TI (I)
Derivative constant TD (D)
P
1
R L
|AT1STEPMV|
100
0
0
PI
0.9
R L
|AT1STEPMV|
100
3.33 × L
0
PID
1.2
R L
|AT1STEPMV|
100
2×L
0.5 × L
(c)
PID constant storage
The following processing is performed and the S. AT1 instruction is terminated.
1) The PID constants are stored into the gain (P), integral constant (I) and derivative constant (D).
2) The auto tuning completed (BB16) is turned to 1.
3) The AT1 stepped manipulated value (AT1STEPMV) is subtracted from the manipulated value (MV), and the
result is stored into the manipulated value (MV).
MV = MV - AT1STEPMV
Operation Error
In the following cases, the error flag (SM0) turns ON and the error code is stored in SD0.
Error code
Error definition
When an operation error occurs
4100
When the value of
S1
is either a non-numeric or non-normalized number
When AT1ST < 0, AT1TOUT1 < 0 or AT1TOUT2 < 0
When the execution cycle (SD1500) < 0
250
QnPHCPU
QnPRHCPU