Siemens SIMATIC Manual page 22

Continuous Temperature Controller FB 58 "TCONT_CP"
Manipulated Variable Limitation LMNLIMIT (LMN_HLM, LMN_LLM)
The value of the manipulated variable is limited to the LMN_HLM and LMN_LLM
limits by the LMNLIMIT function. If these limits are reached, this is indicated by the
message bits QLMN_HLM and QLMN_LLM.
If the manipulated variable is limited, the I-action is stopped. If the error moves the
I-action back in the direction of the manipulated variable range, the I-action is
enabled again.
Changing the Manipulated Variable Limits Online
If the range of the manipulated variable is reduced and the new unlimited value of
the manipulated variable is outside the limits, the I-action and therefore the value of
the manipulated variable shifts.
The manipulated variable is reduced by the same amount as the manipulated
variable limit changed. If the manipulated variable was unlimited prior to the
change, it is set exactly to the new limit (described here for the upper manipulated
variable limit).
Manipulated Variable Normalization LMN_NORM (LMN_FAC, LMN_OFFS)
The LMN_NORM function normalizes the manipulated variable according to the
following formula:
LMN = LmnN * LMN_FAC + LMN_OFFS
It can be used for the following purposes:
•
Manipulated variable adaptation with LMN_FAC as manipulated variable factor
and LMN_OFFS manipulated variable offset
The value of the manipulated variable is also available in the peripheral format. The
CRP_OUT function converts the LMN floating-point value to a peripheral value
according to the following formula:
LMN_PER = LMN * 27648/100
With the default values (LMN_FAC = 1.0 and LMN_OFFS = 0.0), normalization is
disabled. The effective manipulated variable is output at output LMN.
2-8
PID Temperature Control
A5E00125039-02