FB_CTRL_PI

Behaviour of the output:

Step response:

ARW:

VAR_INPUT

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

fSetpointValue : Set value of the controlled variable.

fActualValue : Actual value of the controlled variable.

fManSyncValue : Input with which the PI element can be set.

bSync : A rising edge at this input sets the PI element to the value fManSyncValue.

eMode : Input that specifies the block's operating mode.

bHold : A TRUE at this input will hold the internal state (and therefore also the output) constant at its current value, independently of the system deviation.

VAR_OUTPUT

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

fOut : Output of the PI element.

bARWactive : A TRUE at this output indicates that the PI element is being restricted.

eState : State of the function block.

eErrorId : Supplies the error number when the bError output is set.

bError : Becomes TRUE, as soon as an error occurs.

VAR_IN_OUT

VAR_IN_OUT
    stParams        : ST_CTRL_PI_PARAMS;
END_VAR

stParams : Parameter structure of the PI element. This consists of the following elements:

TYPE ST_CTRL_PI_PARAMS
:
STRUCT
    tCtrlCycleTime     : TIME     :=  T#0ms; (* controller
cycle time [TIME] *)
    tTaskCycleTime     : TIME     :=  T#0ms; (* task cycle time
[TIME] *)
    tTn        : TIME     :=  T#0ms; (* integral action
time Tn *)
    fKp        : FLOAT    :=  0;     (* proportional
gain *)
    fOutMaxLimit       : FLOAT    :=  1E38;  (* maximum output
limit *)
    fOutMinLimit       : FLOAT    := -1E38;  (* minimum output
limit *)
    bARWOnIPartOnly    : BOOL     := FALSE;  (* FALSE: Hold the
I-part if the entire control output reaches a limit. *)
                         (* TRUE: Hold the
I-part if only the I-part reaches a limit. *)
END_STRUCT
END_TYPE

tCtrlCycleTime : 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 : 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 : Integral action time

fKp : Controller amplification / transfer coefficient

fOutMaxLimit : 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 : 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: If this parameter is FALSE (the default 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)

Requirements