FB_CTRL_PTt

FB_CTRL_PTt 1:

The function block provides an PTt transfer element in the functional diagram.

Transfer function

This function block contains internally an array of 500 elements with which the input values can be delayed. When using the tCtrlCycleTime this results in a maximum delay of "500 * tCtrlCycleTime". If this maximum delay is insufficient, the sampling time is extended internally to make it possible to reach the requested dead time. It should, however, be remembered that this process involves increasing the time between the discretization steps. If a new sampling time has been calculated, this is indicated by a TRUE on the bSampleRateChanged output.

VAR_INPUT

VAR_INPUT
    fIn            : FLOAT;
    fManSyncValue  : FLOAT;
    bSync          : BOOL;
    eMode          : E_CTRL_MODE;
END_VAR

Name	Type	Description
fIn	FLOAT	Input value of the PTt element
fManSyncValue	FLOAT	Input value to which the PTt element can be set, or that is issued at the output in manual mode.
bSync	BOOL	A rising edge at this input sets the PTt element to the value "fManSyncValue".
eMode	E_CTRL_MODE	Input that specifies the operation mode of the function block.

VAR_OUTPUT

VAR_OUTPUT
    fOut                : FLOAT;
    bSampleRateChanged  : BOOL;
    eErrorId            : E_CTRL_ERRORCODES;
    bError              : BOOL;
END_VAR

Name	Type	Description
fOut	FLOAT	Output of the PTt element
bSampleRate Changed	BOOL	Output that indicates whether the function block has internally reduced the sampling rate because of the array being used to delay the input signal not otherwise providing sufficient room.
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_PTt_PARAMS;
END_VAR

Name	Type	Description
stParams	ST_CTRL_PTt_ PARAMS	Parameter structure of the PTt element

stParams consists of the following elements:

TYPE ST_CTRL_PTt_PARAMS :
STRUCT
    tCtrlCycleTime  : TIME := T#0ms; 
    tTaskCycleTime  : TIME := T#0ms; 
    fKp             : FLOAT := 0; 
    tTt             : TIME := T#0ms;
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.
fKp	FLOAT	Controller amplification / transfer coefficient
tTt	TIME	Dead time