Envelope
Calculates the envelope of a time signal.
The documentation of the corresponding PLC function block can be found here: FB_CMA_Envelope
For time-synchronous presentation and further processing, see the section Timeshift.
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.
- Number of Channels: defines the number of independent channels. This must be greater than zero.
Output values
- Output: output array with half window length containing the calculated envelope.
- 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.
Time shift
Due to the use of the Welch method (50% overlap) for the analysis as well as a segmented convolution of the analytical signal in the synthesis, four complete data buffers of length nWindowLength/2 are needed to calculate a valid output signal. Furthermore, the result is delayed by (nFFTLentgth + nWindowLength)/2 samples. This can be corrected by a suitable selection of the Time Shift at the channel of the output.
