Siemens SIMATIC Manual page 24

Continuous Temperature Controller FB 58 "TCONT_CP"
Note
•
The controller parameters are only written back to the controller with
UNDO_PAR or LOAD_PID when the controller gain is not 0:
LOAD_PID copies the parameters only if the relevant GAIN is <> 0 (either of
the PI or PID parameters). This strategy takes into account the situation that
no tuning has yet been made or that PID parameters are missing. If
PID_ON = TRUE and PID.GAIN = FALSE were set, PID_ON will be set to
FALSE and the PI parameters copied.
•
D_F, PFAC_SP are set to default values by the tuning. These can then be
modified by the user. LOAD_PID does not change these parameters.
•
With LOAD_PID, the control zone is always recalculated
(CON_ZONE = 250/GAIN) even when CONZ_ON = FALSE is set.
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PID Temperature Control
A5E00125039-02