FB_CTRL_PI

FB_CTRL_PI 1:

The function block provides a PI transfer element in the functional diagram.

Behavior of the output

Step response

FB_CTRL_PI 3:

ARW

FB_CTRL_PI 4:

VAR_INPUT

VAR_INPUT
    fSetpointValue    : FLOAT;
    fActualValue      : FLOAT;
    fManSyncValue     : FLOAT;
    bSync             : BOOL;
    eMode             : E_CTRL_MODE;
    bHold             : BOOL;
END_VAR

Name	Type	Description
fSetpointValue	FLOAT	Setpoint of the controlled variable
fActualValue	FLOAT	Actual value of the controlled variable
fManSyncValue	FLOAT	Input with which the PI element can be set.
bSync	BOOL	A rising edge at this input sets the PI-element to the value "fManSyncValue".
eMode	E_CTRL_MODE	Input that specifies the operation mode of the function block.
bHold	BOOL	A TRUE at this input will hold the internal state (and therefore also the output) constant at its current value, independently of the control deviation.

VAR_OUTPUT

VAR_OUTPUT
    fOut          : FLOAT;
    bARWactive    : BOOL;
    eState        : E_CTRL_STATE;
    eErrorId      : E_CTRL_ERRORCODES;
    bError        : BOOL;
END_VAR

Name	Type	Description
fOut	FLOAT	Output of the PI element
bARWactive	BOOL	A TRUE at this output indicates that the PI-element is being restricted.
eState	E_CTRL_STATE	State of the function block
eErrorId	E_CTRL_ ERRORCODES	Supplies the error number when the output `bError` is set.
bError	BOOL	Becomes TRUE, as soon as an error occurs.

VAR_IN_OUT

VAR_IN_OUT
    stParams        : ST_CTRL_PI_PARAMS;
END_VAR

Name	Type	Description
stParams	ST_CTRL_PI_ PARAMS	Parameter structure of the PI element

stParams consists of the following elements:

TYPE ST_CTRL_PI_PARAMS:
STRUCT
    tCtrlCycleTime     : TIME := T#0ms; 
    tTaskCycleTime     : TIME := T#0ms; 
    tTn                : TIME := T#0ms; 
    fKp                : FLOAT := 0; 
    fOutMaxLimit       : FLOAT := 1E38; 
    fOutMinLimit       : FLOAT := -1E38; 
    bARWOnIPartOnly    : BOOL := FALSE; 
END_STRUCT
END_TYPE

Name	Type	Description
tCtrlCycleTime	TIME	Cycle time with which the control loop is processed. This must be greater than or equal to the TaskCycleTime. The function block uses this input value to calculate internally whether the state and the output values have to be updated in the current cycle.
tTaskCycleTime	TIME	Cycle time with which the function block is called. If the function block is called in every cycle this corresponds to the task cycle time of the calling task.
tTn	TIME	Integral action time
fKp	FLOAT	Controller amplification / transfer coefficient
fOutMaxLimit	FLOAT	Upper limit at which integration is halted and to which the output is limited (ARW measure). Reaching this limit is indicated by a TRUE at the `bARWActive` output.
fOutMinLimit	FLOAT	Lower limit at which integration is halted and to which the output is limited (ARW measure). Reaching this limit is indicated by a TRUE at the `bARWActive` output.
bARWOnIPartOnly	BOOL	If this parameter is FALSE (the standard setting), the integration of the I-component is halted if the complete controller output reaches the upper or lower limit. If it is TRUE, the integration is halted if the I-component (the output of the integrator) reaches some limit. (Cf. functional diagram.)