ControlPIext
ControlPIext (FB)
ControlPIext (FB)FUNCTION_BLOCK ControlPIext
Short description
Proportional-integral acting controller (PI controller), parameters as inputs. The direction of action (inverted / direct) is also adjustable. Typical application: control loops with actuators that have no storing character.
Representation
Interfaces
Inputs
rX
REAL
Analog measured value
rW
REAL
Analog setpoint
xEn
BOOL
Enable of the controller
rYDisabled
REAL
0.0
Disabled value
rInitValue
REAL
0.0
Initialization 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 exceeded
Setpoints / parameters
rOffset
REAL
0.0
Offset
eAction
eControlMode
eControlMode.Inverted
Direction of action of the controller (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) as follows: Output signal: rY = Proportional part + Integral part Proportional part: Proportional part = rKp * control deviation Control deviation: Control deviation = rW - (rx + rOffset) [Direction of action - Inverted: eAction = eControlMode.Inverted] Control deviation = rX - (rW + rOffset) [Direction of action - Direct: eAction = eControlMode.Direct] Integral part: Integral part = (Proportional part * (sampling time / reset time)) + Integral part (t-sampling time) Legend: t-sampling time … time point that 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 part remains constant Control deviation = 0: The integral part remains constant Depending on the controller's direction of action eAction the measured and set values are determined as follows:
| **eAction** | Control deviation | Function | |-------------------------|-------------------------------|-----------------------| | eControlMode.Inverted | *rW* - ( *rx* + **rOffset** ) | Direction of action - Inverted | | eControlMode.Direct | *rX* - ( *rW* + **rOffset** ) | Direction of action - Direct |
Integral part
The integral part is limited both upwards and downwards by the following absolute limits: Upper limit = rMax - Proportional part Lower limit = rMin - Proportional part
Enable input xEn
If the enable input is not active (xEn = FALSE) the disabled value rYDisabled is transferred to the output rY (precondition: eManModeN = eManNum.Auto) and limited by the absolute limits. The integral part is set to 0.0. If the enable input is active (xEn = TRUE) the output signal is calculated according to the formula above and passed to the output rY (precondition: eManModeN = eManNum.Auto) and limited by the absolute limits. On each rising edge of the enable input xEn the control process is restarted.
Restart of the controller
On each rising edge of the enable input xEn the control process is restarted. (Preconditions: eManModeN = eManNum.Auto and xEn = TRUE) The integral part is set to the difference between rInitValue and the proportional part.
Control deviation rDiff
The control deviation corresponds to the value of the control deviation according to the above formula.
Proportional part of the output signal rPartP
This output always provides the proportional part of the output signal, see description above.
Integral part of the output signal rPartI
This output always provides the integral part of the output signal, see description above.
Absolute limits rMin and rMax
The controller's output signal rY is limited downwards by the absolute limit rMin and upwards by rMax . The absolute limit rMin is set to the current value of rMax - 0.1 if it is >= the current value of rMax . The only exception is manual operation for the controller output signal (eManModeN = eManNum.Man).
Status - limit exceeded xLimitActive
The limit-exceeded status is activated (xLimitActive = TRUE) if a limit is exceeded upwards or downwards (xEn = TRUE). The limit-exceeded status is not activated (xLimitActive = FALSE) if no limit is exceeded or the enable signal is deactivated (xEn = FALSE). A limit is considered exceeded 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 mode and vice versa. In manual mode the output signal rY takes over the output signal in manual mode rManValue. The integral part is set to the difference between rInitValue and the proportional part.
eManModeN
rY
Function
eManNum.Auto
signal according to formula / disabled value
Automatic mode - output signal
eManNum.Man
rManValue
Manual mode - output signal
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
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