9.6
Limitation, general (LIM)
9.6.1
Purpose and activation
The LIM function (general limiting function) overrides the sequence controller's
normal control function.
Purpose of LIM
To activate the function, select input identifier SAT for the room and the supply air
temperature and, in the configuration, in setting value STRATGY, control strategy
LIM for controller 1 (also refer to subsection 9.2.1 “Selecting the control strategy”).
Activation:
Controller 1, type A
To activate the function, assign an input Xx to the LIM label at the controller 2
function block.
Activation:
Controller 2, type A
controllers 1+2, type U
If other influences act on the sequence controller at the same time, the order of
priorities applies as shown in subsection 9.1.4 “Function priorities”.
9.6.2
Operating principle
If the controlled variable crosses one of the limit setpoints, the limitation function
with PI control (LIM XP, LIM TN) overrides the normal control function to maintain
the limit setpoint. We distinguish between:
Limitation with PI
control
•
Absolute limitation
•
Relative limitation
If you only want one of these functions, you can disable the other by setting the
setpoints a long way out of range.
You can define one setpoint each for maximum and minimum limitation (LIM MAX,
LIM MIN).
Absolute limitation
Supply air temperature or supply air humidity limitation:
Application example
x
w
T
T
[
LIM MAX
]
[
LIM MIN
]
−
[
LIM COOL
]
Limitation max
Limitation min
31
01
S
33
en
Acts an all sequences
!! Not meaningful with cascade control !!
Setpoint adjustment
121 / 174
Siemens
Universal Controllers RLU2…
CE1P3101en
Building Technologies
Controller (CTLOOP x)
29.08.2008
