Siemens SIMATIC S7-1200 Function Manual page 479

Manual value processing (MAN_ON, MAN)
You can change over between manual and automatic mode. In manual mode, the
manipulated variable is corrected to a manually selected value.
The integral action (INT) is set internally to LMN - LMN_P - DISV and the derivative action
(DIF) is set to 0 and synchronized internally. Changeover to automatic mode is therefore
bumpless.
Note
The MAN_ON parameter has no effect during tuning.
Output value limit LMNLIMIT (LMN_HLM, LMN_LLM)
The LMNLIMIT function is used to limit the output value to the limits LMN_HLM and
LMN_LLM. If these limits are reached, this is indicated by the message bits QLMN_HLM and
QLMN_LLM.
If the output value is limited, the integral action is halted. If the control deviation moves the
integral action back in the direction of the output range, the integral action is enabled again.
Changing the Manipulated Value Limits Online
If the range of the output value is reduced and the new unlimited value of the output value is
outside the limits, the integral action and therefore the output value shifts.
The output value is reduced by the same amount as the output value limit changed. If the
output value was unlimited prior to the change, it is set exactly to the new limit (described
here for the high output value limit).
Scaling of output value LMN_NORM (LMN_FAC, LMN_OFFS)
The LMN_NORM function normalizes the output value according to the following rule:
LMN = LmnN * LMN_FAC + LMN_OFFS
It can be used for the following purposes:
● Output value scaling with LMN_FAC as output value factor and LMN_OFFS as output
value offset.
The output value is also available in I/O format. The CRP_OUT function converts the LMN
floating-point value to an I/O value according to the following rule:
LMN_PER = LMN * 27648/100
The scaling is switched off with the default values (LMN_FAC = 1.0 and LMN_OFFS = 0.0).
The effective output value is sent to output LMN.
PID control
Function Manual, 03/2017, A5E35300227-AC
Instructions
9.4 PID basic functions
479