Event-based frequency analysis

Block diagram

Program parameters

The table below shows a list of important parameters for the configuration of the magnitude spectrum function block.

Event-based buffering of the input signal

The program block CollectData controls the event-based sampling of the input signal. The input parameters are defined as follows:

PROGRAM CollectData
VAR_INPUT
    bTrigger     : BOOL;     // Trigger signal, start with rising edge
END_VAR
VAR_IN_OUT
    aInputSignal : ARRAY[1..cOversamples] OF LREAL;  // input time signal
END_VAR

The inverse of the trigger signal bTrigger_ and the current state of buffer are stored locally.

VAR
    bTrigger_          : BOOL := FALSE;
    nSourceState       : UINT := 0;
    nActualBuffersSent : ULINT := 0;
    nBuffersToSent     : ULINT := 2;

    // ...

END_VAR

Event-controlled sampling of the signal takes place when the trigger signal has a rising edge and the buffer is ready, i.e. state 0.

IF (bTrigger AND NOT bTrigger_) AND nSourceState = 0 THEN
    nActualBuffersSent := fbSource.nCntResults;  // check number of sent MultiArrays from fbSource
    fbSourceState := 1;
END_IF
bTrigger_ := bTrigger;

The following code shows the actual event-based buffering of the signal via the source function block.

CASE nSourceState OF

    1: // if <nBuffersToSent> MultiArrays has been sent, stop buffering

       fbSource.Input1D( pDataIn      := ADR(aInputSignal),
                         nDataInSize  := SIZEOF(aInputSignal),
                         eElementType := eMA_TypeCode_LREAL,
                         nWorkDim     := 0,
                         pStartIndex  := 0,
                         nOptionPars  := 0);

       IF (fbSource.nCntResults-nActualBuffersSent) = nBuffersToSent THEN
           nSourceState := 2;
       END_IF

    2: // reset Source Buffer and wait for next trigger hit

       fbSource.ResetData();
       nSourceState := 0;

END_CASE;

The buffered signal data is subsequently relayed to the magnitude spectrum function block. The buffered signal is processed in the same way as shown in the Magnitude spectrum: sample.

Requirements