Multi Band RMS

Calculated RMS value for single- and multi-channel real-valued time series for configurable frequency bands.

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

The documentation of the TwinCAT 3 Condition Monitoring PLC library can be found here: Overview.

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.
Max Number of Bands: this value specifies the maximum number of frequency bands for which the RMS value is calculated.
WindowType: Defines the used window function (of the type E_CM_WindowType). A good default value is the window type eCM_HannWindow.
Config: MaxBands x [fmin, fmax]: definition of the configurable lower and upper limit of the frequency bands.
Sample Rate: sampling rate of the incoming time signal. The value is used for the scaling of the result in Hz.
Number of Channels: defines the number of independent channels. This must be greater than zero.
Use Recommended Overlap: if selected, a recommended overlap is calculated internally (see F_CM_CalculateRecommendedOverlap).
Window Overlap: defines the number of overlapping samples. This must be greater than or equal to 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).
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)
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: channel and band specific RMS values.
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.