Description

Function description

The function block represents a differentiator element with an output OUT delayed by the lag time constant LAG.

The function block contains the following operating mode:

Tracking
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 for OUT is:

The formula of calculation is:

Meaning of the sizes

Variable	Description
	Value of the input IN from the current cycle
	Value of input IN from the previous cycle
	Value of the output OUT 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_Instance (IN:=InputVariable, 
    GAIN:=DifferentiationGain,  LAG:=TimeDelayConstant,  
    TR_I:=InitializationInput, TR_S:=InitializationType, 
    OUT=>OutputDerivativeUnit)

Representation in ST

Representation:

LEAD_Instance (IN:=InputVariable, 
    GAIN:=DifferentiationGain,  LAG:=TimeDelayConstant,  
    TR_I:=InitializationInput, TR_S:=InitializationType, 
    OUT=>OutputDerivativeUnit) ;

Parameter description

Description of input parameters:

Parameter	Data type	Description
IN	REAL	Input value
GAIN	REAL	Gain of the differentiation
LAG	TIME	Delayed time constants
TR_I	REAL	Initialization input
TR_S	BOOL	Initialization type "1" = Operating mode Tracking "0" = Automatic operating mode

Description of output parameters:

Parameter	Data type	Description
OUT	REAL	Output derivative unit with smoothing

Runtime error

For a list of all block error codes and values, see Conditioning.

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.