Spike Energy Spectrum

Analysis of peak energy of high-frequency signal components.

The documentation of the corresponding PLC function block can be found here: FB_CMA_SpikeEnergySpectrum

Configuration options

• FFT Length: is the length of the FFT. It must be greater than one and an integral power of two.
• Window Length: is the length of the analysis window in samples. The length must be greater than one and an even number.
• Sample Rate: sampling rate of the incoming time signal. The value is used for the scaling of the result in Hz.
• IIR Filter Order: defines the order of the IIR filter used.
• WindowType: Defines the used window function (of the type E_CM_WindowType). A good default value is the window type eCM_HannWindow.
• Scaling Type: Enables the selection of the scaling (of the type E_CM_ScalingType) to be used, in case absolute scaling is required. The default value is eCM_DiracScaling. When selecting the scaling the type of signal should be considered: either deterministic signals or wide-band signals with stochastic portion. Both types require different scalings.
• Number of Channels: defines the number of independent channels. This must be greater than zero.
• Transform to Decibel: is a 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).
• Window Overlap: defines the number of overlapping samples. This must be greater than or equal to zero.
• Decibel Threshold: is a 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. (The purpose is the avoidance of value range errors. The logarithm of zero is not defined and strives infinitely towards minus for the limit value of small arguments. The same applies to the argument of the number zero, arg(0). The smallest possible value is 2.3e-308)
• Use Recommended Overlap: if selected, a recommended overlap is calculated internally (see F_CM_CalculateRecommendedOverlap).
• Config: Ch x [decay, fmin, fmax]: definition of the configurable parameters: the decay time and the considered frequency band (by lower and upper limits). The decay time should optimally be chosen so that the peak energy can completely decay, i.e. 'decay time' > 1 / 'error frequency'.
• Window Parameters: contains the free parameters of selected window functions. When using eCM_KaiserWindow, the first entry defines the parameter beta; if eCM_FlatTopWindow is used, all parameters are used. See section Window functions.

Output values

• Output: Output array of length N / 2 + 1 (for FFT length N), which contains the calculated spectral lines of the spike energy spectrum.
• Cnt Results: specifies the number of output arrays calculated.
• New Result: is a Boolean value that indicates whether a new result was obtained in the current cycle.