Description

Function description

The function block produces a velocity limiter of the 1st order with limiting of the manipulated variable.

The output Y follows the input X, but at the maximum gradient rate. Furthermore, the Y output is limited by ymax and ymin. This allows the function block to adjust signals to the technologically limited pace and limits from controlling elements.

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 ouputs may deliver wrong values.

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.

Properties

The function block has the following properties:

Operating modes Manual, Halt, Automatic
Manipulated variable limiting

Representation in FBD

Representation:

Representation in LD

Representation:

Representation in IL

Representation:

CAL VLIM_Instance (X:=Input, MODE:=OperatingMode, 
    PARA:=Parameters, YMAN:=ManualManipulatedValue, 
    Y:=Output, STATUS:=Output_Y_Status)

Representation in ST

Representation:

VLIM_Instance (X:=Input, MODE:=OperatingMode, 
    PARA:=Parameters, YMAN:=ManualManipulatedValue, 
    Y:=Output, STATUS:=Output_Y_Status)

VLIM parameter description

Description of input parameters:

Parameter	Data type	Description
X	REAL	Input
MODE	Mode_MH	Operating mode
PARA	Para_VLIM	Parameter
YMAN	REAL	Manually manipulated value

Description of input / output parameters:

Parameter	Data type	Description
Y	REAL	Output

Description of output parameters:

Parameter	Data type	Description
STATUS	Stat_MAXMIN	Y output status

Parameter description Mode_VLIM

Data structure description

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

Parameter description Para_VLIM

Data structure description

Element	Data type	Description
rate	REAL	Maximum velocity (maximum x’ / sec)
ymax	REAL	Upper limit
ymin	REAL	Lower limit

Parameter description Stat_MAXMIN

Data structure description

Element	Data type	Description
qmax	BOOL	"1" = Y has reached the upper control limit
qmin	BOOL	"1" = Y has reached the lower control limit

Runtime error

An error message is returned if

an invalid floating point number lies at input YMAN or X,
ymax < ymin.

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.