Siemens SIMATIC Manual page 41

Tuning at the Operating Point without Setpoint Step Change
The tuning manipulated variable (LMN0 + TUN_DLMN) is applied by setting the
start bit TUN_ST (transition Phase 1 -> 2). When you change the setpoint, the new
setpoint takes effect only when the point of inflection is reached (this is when the
controller switches to automatic).
The user is responsible for selecting the magnitude of the manipulated variable
change (TUN_DLMN) according to the permitted process variable change. The
sign of TUN_DLMN must be set depending on the intended process variable
change (take into account the direction in which the control is operating).
Caution!
If you excite the process with TUN_ST, there is no safety turn off at 75%. Tuning
is terminated when the point of inflection is reached. In noisy processes, the point
of inflection can, however, be significantly exceeded.
Protection Against Operator Input Errors
Operator Error
Setting TUN_ON and setpoint
step change or TUN_ST at the
same time
Effective TUN_DLMN < 5% (end
of Phase 1)
PID Temperature Control
A5E00125039-02
STATUS and Result
Transition to Phase 1,
however tuning is not started.
•
SP_INT = SPold or
•
TUN_ST = FALSE
STATUS_H = 30002
•
Transition to Phase 0
•
TUN_ON = FALSE
•
SP = SPold
Controller Tuning in FB 58 "TCONT_CP"
Comment
The setpoint change is canceled.
This prevents the controller
controlling to the new setpoint and
leaving the steady state operating
point unnecessarily.
Tuning is aborted.
The setpoint change is canceled.
This prevents the controller
controlling to the new setpoint and
leaving the steady state operating
point unnecessarily.
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