ST_PMA_Harmonics_InitPars

Function block-specific structure with initialization parameters that are evaluated when the function blocks FB_PMA_Harmonics_1Ph and FB_PMA_Harmonics_3Ph are initialized.

Syntax

Definition:

TYPE ST_PMA_HarmonicAnalysis_InitPars :
STRUCT
    fSampleRate          : LREAL := 1000;    // Sample rate
    fBaseFreq            : LREAL := 50.0;    // Multiple of base frequence is used for band limit definition
    nFFT_Length          : UDINT := 512;     // Length of FFT
    nWindowLength        : UDINT := 400;     // Length of FFT window
    nNumBands            : UDINT := 10;      // Number of bands
    fBandwidth           : LREAL := 4.0;     // Whole bandwidth for each frequency band, min 1.0
    eWindowType          : E_PMA_WindowType := E_PMA_WindowType.HannWindow; // Window  function used
    bTransformToDecibel  : BOOL  := TRUE;    // Transform result to decibel
    fDecibelThreshold    : LREAL := 1.3E-308;// Logarithm threshold for decibel transformation
    bTransformToPercent  : BOOL := FALSE;    // Transform result to percent (1^st harmonic=100%)
END_STRUCT
END_TYPE

Parameter

Name	Type	Parameter
fSampleRate	LREAL	Indicates the sampling rate (samples per second) of the input signal.
fBaseFreq	LREAL	Frequency of the first harmonic.
nFFT_Length	UDINT	Length of the FFT. It must be greater than one and an integral power of two.
nWindowLength	UDINT	Length of the analysis window in samples. The length must be greater than one and an even number.
nNumBands	UDINT	Indicates the number of bands for which the RMS is calculated.
fBandwidth	LREAL	Total bandwidth of each RMS band
eWindowType	E_PMA_WindowType	Defines the window function that is used. The window type "„HannWindow" is a good default value. The windowing can be switched off by the use of the window type "RectangularWindow". Further explanations and the list of possible window functions can be found in the introductory section Window functions.
bTransformToDecibel	BOOL	Boolean value that indicates whether the result of the FFT is to be transformed to the decibel scale, according to transformation x → 20 * log10(x).
fDecibelThreshold	LREAL	Very small floating point value greater than zero. Values that are less than this number are replaced with this value before any transformation to the decibel scale, since the logarithm of zero is not defined mathematically. The smallest possible value is 3.75e-324.
bTransformToPercent	BOOL	Boolean value indicating whether the result should be output in percent. The first harmonic corresponds to 100%.

	Window length The value of nWindowLength must be less or equal the value of nFFT_Length. The length of the FFT can orient itself to the required frequency resolution. Typically a value of about 3/4 of the FFT length is used as the window length.

If nFFT_Length is greater than nWindowLength, the frequency resolution of the FFT (and therefore also the length of the return values vector) is increased. The length difference is filled with zeros before the Fourier transform . This can be useful for achieving a higher frequency resolution, or for avoiding circular aliasing in calculations with inverse transformation in the time domain . Despite the higher frequency resolution, however, the result contains no more information.