ST_CM_OrderPowerSpectrum_InitPars

Function block-specific structure with initialization parameters, which are analyzed when the function block is initialized.

TYPE ST_CM_OrderPowerSpectrum_InitPars EXTENDS ST_CM_Object_InitPars :
STRUCT
    fSampleRateSignal    : LREAL := 1000;                             (* Sample rate in Hertz of vibration signal. *)
    fSampleRatePosition  : LREAL := 1000;                             (* Sample rate in Hertz of positions. *)
    fPositionScaling     : LREAL := 1;                                (* One rotation needs to be represented by 1. *)
    fMaxRPM              : LREAL := 1800;                             (* Max. rotations per minute. *)
    nFFT_Length          : UDINT := 512;                              (* Length of FFT. *)
    nWindowLength        : UDINT := 400;                              (* Length of analysis window. *)
    fDecibelThreshold    : LREAL := cCM_MinArgLog10;                  (* Minimum argument of decadic logarithm for 64- bit IEEE 754 arithmetic. *)
    bTransformToDecibel  : BOOL := TRUE;                              (* Transform to decibel. *)
    eWindowType          : E_CM_WindowType := eCM_HannWindow;         (* Window type. *)
    aWindowParameters    : T_CM_WindowParameters := [2.5,1,1,1,1];    (* Window parameters for specific windows, e.g. FlatTop. *)
    nOverlap             : UDINT := -1;                               (* Size of overlap in samples. *)
    eScalingType         : E_CM_ScalingType := eCM_DiracScaling;      (* Scaling type. *)
    nChannels            : UDINT := 1;                                (* Number of channels. *)
END_STRUCT
END_TYPE

• fSampleRateSignal defines the sampling rate of the incoming vibration signal in Hertz.
• fSampleRatePosition defines the sampling rate of the incoming position signal in Hertz. This may be unequal to fSampleRateSignal.
• fPositionScaling is the scaling factor for the position signal. A full revolution must be represented by this value. If the position signal is scaled in degrees, fPositionScaling = 360 must be set. If the position signal is scaled so that a full revolution of the shaft produces the value 2*pi, then fPositionScaling = 2 * pi.
• fMaxRPM is the maximum number of revolutions per minute. With the fSampleRateSignal, this parameter defines the maximum resolvable order of the order spectrum.

All other parameters are analogous to the parameterization of the power spectrum, see ST_CM_PowerSpectrum_InitPars.

• nFFT_Length is the length of the FFT. It must be greater than one and an integral power of two.
• nWindowLength is the length of the analysis window in samples. The length must be greater than one and an even number.
• fDecibelThreshold 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, which is equivalent to the constant cCM_MinArgLog10.)
• bTransformToDecibel 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).
• eWindowType defines the used window function (of the type E_CM_WindowType). A good default value is the window type eCM_HannWindow.
• aWindowParameters 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.
• nOverlap defines the number of overlapping samples. This must be greater than or equal to zero. If the value cCM_OverlapRecommended is selected, a recommended overlap is calculated internally (see F_CM_CalculateRecommendedOverlap); the value cCM_OverlapInactive deactivates the internally used buffer and sets the value to zero.
• eScalingType enables the selection of the scaling to be used (of the type E_CM_ScalingType), 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.
• nChannels defines the number of independent channels. This must be greater than zero.