Crest factor

Block Diagram

Program parameters

The table below shows a list with important configuration parameters for the function block for calculating the crest factor.

Global constants

These parameters are defined in the global variable list as constants.

VAR_GLOBAL CONSTANT
    cOversamples  : UDINT := 10;    // oversampling factor
    cChannels          : UDINT := 2;     // number of channels
    cBufferLength      : UDINT := 2000;  // size of buffer 
END_VAR

Code for Control Task

Following code snippet shows the declaration in MAIN program:

VAR CONSTANT 
     cInitSource       : ST_MA_MultiArray_InitPars := ( eTypeCode := eMA_TypeCode_LREAL, nDims := 2, aDimSizes := [cChannels, cBufferLength]);
END_VAR

VAR 
     nInputSelection : UDINT := 1;
     aCrestFactor      : ARRAY[1..cChannels] OF LREAL; 
     nSampleIdx    : UDINT;
     nChannelIdx       : UDINT; 
     aEl3632 AT %I*    : ARRAY[1..cChannels] OF ARRAY[1..cOversamples] OF INT; // input from hardware e.g. EL3632
     aBuffer  : ARRAY[1..cChannels] OF ARRAY[1..cOversamples] OF LREAL; 
     fbSource      : FB_CMA_Source := (stInitPars := cInitSource, nOwnID := eID_Source, aDestIDs := [eID_Crest]); // Initialize source 
     fbSink        : FB_CMA_Sink := (nOwnID := eID_Sink);    
END_VAR

Method calls in Main program:

// Collect data in a source 
fbSource.Input2D(pDataIn := ADR(aBuffer),
          nDataInSize := SIZEOF(aBuffer), 
          eElementType := eMA_TypeCode_LREAL,
          nWorkDim0 := 0,
          nWorkDim1 := 1,
          pStartIndex := 0,
          nOptionPars := 0 ); 

// Push results to sink
fbSink.Output1D(pDataOut := ADR(aCrestFactor), 
          nDataOutSize := SIZEOF(aCrestFactor), 
          eElementType := eMA_TypeCode_LREAL, 
          nWorkDim := 0, 
          nElements := 0,
          pStartIndex := 0,
          nOptionPars := 0,
          bNewResult => bNewResult); 

Code for CM Task

Declaration in MAIN_CM program:

VAR CONSTANT 
     cInitCrest : ST_CM_CrestFactor_InitPars := ( nChannels := cChannels, nBufferLength := cBufferLength );
END_VAR

VAR 
     fbCrest : FB_CMA_CrestFactor := (stInitPars := cInitCrest, nOwnID:= eID_Crest, aDestIDs:= [eID_Sink]); // Initialize crest   
END_VAR

Method calls in MAIN_CM program:

fbCrest.Call();

The result of the sample code can be checked for a sinusoidal signal of arbitrary amplitude and frequency as the input signal. The crest factor, in this case first element of aCrestFactor, must be equal to 3.01 dB.

Requirements