Description

Function description

The function block implements a PD element with following low-pass filter.

The function block has the following properties:

Definable delay of the D-component
Operating modes Manual, Halt, Automatic

NOTE: This function block performs an internal initialization in the first program cycle after a warm start or cold start (e.g. application download or power cycle) of the PLC program.

Due to this, you have to make sure that the function block is invoked in the first program cycle. In case of inkoving the function block in a later program cycle, the internal initialization will not be performed and the ouput may deliver a wrong value.

WARNING

UNEXPECTED OUTPUT BEHAVIOUR

Make sure that the function block is always invoked in the first program cycle.

Failure to follow these instructions can result in death, serious injury, or equipment damage.

and can be configured as additional parameters.

Formula

The transfer function is:

The formula of calculation is:

Meaning of the sizes

Variable	Description
	Value of input X from the previous cycle
	Value of the output Y from the previous cycle
dt	is the time differential between the current cycle and the previous cycle

Representation in FBD

Representation:

Representation in LD

Representation:

Representation in IL

Representation:

CAL LEAD_LAG_Instance (X:=Input, MODE:=OperatingModes, 
    PARA:=Parameter, YMAN:=ManualControlValue, Y:=Output)

Representation in ST

Representation:

LEAD_LAG_Instance (X:=Input, MODE:=OperatingModes, 
    PARA:=Parameter, YMAN:=ManualControlValue, Y:=Output) ;

Parameter description LEAD_LAG

Description of input parameters:

Parameter	Data type	Description
X	REAL	Input
MODE	Mode_MH	Operating mode
PARA	Para_LEAD_LAG	Parameter
YMAN	REAL	Manual value manipulated value

Description of input / output parameters:

Parameter	Data type	Description
Y	REAL	Output

Parameter description Mode_MH

Data structure description

Element	Data type	Description
man	BOOL	"1" = Manual operating mode
halt	BOOL	"1" = Halt mode

Parameter description Para_LEAD_LAG

Data structure description

Element	Data type	Description
gain	REAL	Gain factor
lead	TIME	Derivative time constant
lag	TIME	Delayed time constants

Runtime error

An error message is returned when an invalid floating point number lies at input YMAN or X.

NOTE: For a list of all block error codes and values, see CLC_PRO.

REAL

The REAL type is encoded in a 32 bit format.

The possible value ranges are shown in the figure below:

When a result is:

between -1,175494e-38 and 1,175494e-38, it is considered to be a DEN;
less than -3.402824e+38, the symbol -INF (for - infinity) is displayed;
greater than +3.402824e+38, the symbol INF (for + infinity) is displayed;
undefined (square root of a negative number), the symbolNAN is displayed.

NOTE: The IEC 559 standard defines two classes of NAN: the silent NAN (QNAN) and the signaling NAN (SNAN). A QNAN is a NAN with a most significant fraction bit while an SNAN is a NAN without a most significant fraction bit (bit number 22). QNANs can be propagated via most arithmetic operations without throwing an exception. As for SNANs, they generally indicate n invalid operation when they are used as operands in arithmetic operations (see %SW17 and %S18).

NOTE: When a DEN (non-standardized number) is used as an operand, the result is not significant.