Settling Of The Manipulated Variable; Principle - Siemens LMV51 Series Basic Documentation

Settling of the
manipulated variable

Principle

Description (graph)
Siemens Building Technologies
HVAC Products
Settling of the manipulated variable is used in modulating mode to avoid unnecessary
drive pulses, thus extending the life of the controlling elements.
Settling of the manipulated variable is active across the entire working range so that a
neutral zone is no longer required.
For setting the settling of the manipulated variable, a parameter is used that can be set
by the user, it is called «Minimum possible step of the controlling element».
Parameter: MinActuatorStep
Based on this value, the «currently smallest step of the controlling element» (ASmincur)
is calculated, depending on the control differential.
If the difference between the newly calculated manipulated variable and the manipulated
variable delivered last is smaller than ASmincur, the last manipulated variable will be
maintained and the newly calculated manipulated variable rejected.
Calculation of the «currently smallest possible step of the controlling element» (ASmincur)
is made differently for the 2 ranges:
a) Value of control differential smaller than setpoint * MinActuatorStep
b) Value of control differential greater than setpoint * MinActuatorStep
Currently smallest
step of controlling
element
(ASmincur)
1
MinActuatorStep
7550d10E/0502
Setpoint MinActuatorStep
Parameter: MinActuatorStep: (0.5...10 %)
Settling of the manipulated variable is based on the following considerations:
Sector 1
Actual value very close to the setpoint
-
Range of a small number of large steps of the controlling element
-
In this range, the setpoint can be maintained with a small number of steps of the
controlling element. If required, large changes of the controlling element are possible - in
contrast to the classical neutral band.
Sector 2
Actual value near the setpoint
-
Range of a large number of small steps of the controlling element
-
In this range, to ensure control, the smallest steps of the controlling element are possible.
Sector 3
Actual value far away from the setpoint
-
Range of a small number of large steps of the controlling element
-
In this range, small steps of the controlling element are suppressed since they would
not yet have any major impact.
Basic Documentation LMV51...
5 Temperature or pressure controller (internal load controller LC)
2 3
Control differential
65/157
CC1P7550en
29.05.2002