ControlPIext
ControlPIext (FB)
ControlPIext (FB)FUNCTION_BLOCK ControlPIext
Short description
Proportional-integral acting controller (PI controller), parameters as inputs. The action (inverted / direct) is also configurable. Typical application: control loops with actuators that do not have storing characteristics.
Representation
Interfaces
Inputs
rX
REAL
Analog actual value
rW
REAL
Analog setpoint
xEn
BOOL
Enable of the controller
rYDisabled
REAL
0.0
Shutdown value
rInitValue
REAL
0.0
Initial value for the output signal
rKp
REAL
0.0 …
2.0
Gain factor
rTn
REAL
0.0 …
200.0
Reset time in seconds
rMin
REAL
0.0
Lower absolute limit of the output signal
rMax
REAL
100.0
Upper absolute limit of the output signal
Outputs
rY
REAL
0.0
Controller output signal
rDiff
REAL
Control deviation
rPartP
REAL
Proportional part of the output signal
rPartI
REAL
Integral part of the output signal
xLimitActive
BOOL
Status - limit exceedance
Setpoints / Parameters
rOffset
REAL
0.0
Offset
eAction
eControlMode
eControlMode.Inverted
Controller action (Inverted, Direct)
eManModeN
eManNum
eManNum.Auto
Operating mode for the controller output signal
rManValue
REAL
Output signal in manual mode
Function description
General
This function block contains a proportional-integral acting controller (PI controller). Some parameters are defined as inputs and thus not persistent. This allows the values to be changed continuously by the program. The controller's output signal rY is calculated when the controller is enabled ( xEn = TRUE ) and in the controller's automatic operating mode ( eManModeN = eManNum.Auto ) is calculated as follows: Output signal: rY = Proportional component + Integral component Proportional component: Proportional component = rKp * control deviation Control deviation: Control deviation = rW - ( rx + rOffset ) [ Action - Inverted: eAction = eControlMode.Inverted ] Control deviation = rX - ( rW + rOffset ) [ Action - Direct: eAction = eControlMode.Direct ] Integral component: Integral component = ( Proportional component * ( sampling time / reset time )) + Integral component ( t-sampling time ) Legend: t-sampling time … time point which was one sampling time before the current time t Sampling time … time interval between two calls of the function block t … current time\
Control / Properties - Reset time rTn
It may only take values > 0. rTn >>> Sampling time: The integral component remains constant Control deviation = 0: The integral component remains constant Depending on the controller action eAction the actual and set values are determined as follows:
| **eAction** | Control deviation | Function | |-------------------------|-------------------------------|-----------------------| | eControlMode.Inverted | *rW* - ( *rx* + **rOffset** ) | Action - Inverted | | eControlMode.Direct | *rX* - ( *rW* + **rOffset** ) | Action - Direct |
Integral component
The integral component is limited both upwards and downwards by the following absolute limits: Upper limit = rMax - Proportional component Lower limit = rMin - Proportional component\
Enable input xEn
If the enable input is not active ( xEn = FALSE ) the shutdown value rYDisabled is transferred to the output rY ( prerequisite: eManModeN = eManNum.Auto ) and limited by the absolute limits. The integral component is set to 0.0. With active enable input ( xEn = TRUE ) the output signal is calculated according to the formula above and to the output rY ( prerequisite: eManModeN = eManNum.Auto ) and limited by the absolute limits. On every rising edge at the enable input xEn the control process is restarted. \
Restarting the controller
On every rising edge at the enable input xEn the control process is restarted. ( Preconditions: eManModeN = eManNum.Auto and xEn = TRUE ) The integral component is set to the difference between rInitValue and the proportional component. \
Control deviation rDiff
The control deviation corresponds to the value of the control deviation according to the formula given above. \
Proportional part of the output signal rPartP
The proportional part of the output signal is always available at this output, see the description above. \
Integral part of the output signal rPartI
The integral part of the output signal is always available at this output, see the description above. \
Absolute limits rMin and rMax
The controller's output signal rY is limited downward by the absolute limits rMin and upward rMax . The absolute limit rMin is set to the current value of rMax - 0.1 if it >= the current value of rMax . The only exception is the manual operation for the controller's output signal (eManModeN = eManNum.Man ).\
Status - limit exceedance xLimitActive
The limit exceedance status is activated ( xLimitActive = TRUE ), if an upper or lower limit violation exists ( xEn = TRUE ). The status of the limit violation is not activated ( xLimitActive = FALSE ), if no limit violation exists or the enable signal is deactivated ( xEn = FALSE ). A limit violation exists if the controller's output signal rY reaches / exceeds the upper limit rMax or reaches / falls below the lower limit rMin . \
Operating mode for the controller output signal eManModeN
The parameter eManModeN allows switching the output signal rY from automatic to manual operation and vice versa. In manual mode the output signal takes over rY the output signal in manual mode rManValue. The integral component is set to the difference between rInitValue and the proportional component. \
eManModeN
rY
Function
eManNum.Auto
Signal according to formula / switch-off value
Automatic mode - output signal
eManNum.Man
rManValue
Manual mode - output signal
Visualization
\
Codesys
InOut:
Input
rX
REAL
Input
rW
REAL
Input
xEn
BOOL
Input
rYDisabled
REAL
0
Input
rInitValue
REAL
0
Input
rKp
REAL
2
Input
rTn
REAL
200
Input
rYMin
REAL
0
Input
rYMax
REAL
100
Input Const
rOffset
REAL
0
Input Const
eAction
eControlMode
eControlMode.Inverted
Input Const
eManModeN
eManNum
eManNum.Auto
Input Const
rManValue
REAL
Output
rY
REAL
0
Output
rDiff
REAL
Output
rPartP
REAL
Output
rPartI
REAL
Output
xLimitAktiv
BOOL
Last updated