Siemens SIMATIC Manual page 37

The schematic below illustrates the phases of tuning at the operating point started
with TUN_ST = TRUE:
Temperature
PHASE = 0 PHASE = 1 PHASE
TUN_DLMN
At the end of the tuning (see Section 3.9, Page 3-11), when the block returns to
Phase 0 and TUN_ON = FALSE is set, you can recognize whether or not the
tuning was error free by the STATUS_H parameter.
PID Temperature Control
A5E00125039-02
PHASE = 3, 4, 5
(one cycle)
PHASE = 7
= 2
Point of inflection
LMN
Reset by Block
Controller Tuning in FB 58 "TCONT_CP"
PHASE = 0
PV
Operating point process value
Operating point
manipulated variable
TUN_ON
TUN_ST
Time
3-5