MC_AxUtiAverageDerivative_BkPlcMc (from V3.0)

The function block determines the derivative of a value through numeric differentiation over more than one cycle.

Inputs

VAR_INPUT
    Input:      LREAL:=0.0;
    MinIdx:     DINT:=0;
    MaxIdx:     DINT:=0;
    pBuffer:    POINTER TO LREAL:=0;
END_VAR

Name	Type	Description
Input	LREAL	The raw value of the parameter to be filtered.
MinIdx	DINT	The index of the first filter buffer element to be used.
MaxIdx	DINT	The index of the last filter buffer element to be used.
pBuffer	POINTER	The address of the first filter buffer element.

Inputs/outputs

VAR_INOUT
    Axis:       Axis_Ref_BkPlcMc;
END_VAR

Name	Type	Description
Axis	Axis_Ref_BkPlcMc	Here, the address of a variable of type Axis_Ref_BkPlcMc should be transferred.

Outputs

VAR_OUTPUT
    Output:     LREAL:=0.0;
    Error:      BOOL:=FALSE;
    ErrorID:    UDINT:=0;
END_VAR

Name	Type	Description
Output	LREAL	The filtered value.
Error	BOOL	This output indicates problems with the transferred parameters.
ErrorID	UDINT	In the event of an error, coded information about the type of problem is reported here.

Behavior of the function block

With each call the function block checks the address of the filter buffer pBuffer and the indices of the elements MinIdx and MaxIdx to be used. If the transferred values are obviously nonsensical, the system responds with Error and coded information in ErrorID. Otherwise, with each call Input is entered in the filter buffer, and the average value of the modification over the set of values available in the buffer is formed and returned as Output.

	The set of values for averaging contains (MaxIdx - MinIdx + 1) values. The measuring time is determined by multiplication of this number with the cycle time.

	The principle of sliding averaging leads to a delay amounting to half the measuring time. If the filtered parameter can be used in a control loop, the resulting frequency-dependent phase shift can lead to restrictions for the parameter selection.

	The function block has no way to fully check the transferred values of pBuffer, MinIdx and MaxIdx. The user must ensure that these values can be used safely. Otherwise may behave in an unpredictable manner (overwriting of memory) or abortion of the PLC operation.