FFT (One Time Signal)

FFT (One Time Signal)

Use this dialog box to run a fast Fourier transform (FFT) of one or several signal pairs. Various window functions, section-wise calculations with and without overlapping, and various averaging procedures are available for all FFT calculations.

Open Dialog Box in DIAdem

Settings

	Time channel (X)	Specifies the data channel containing the time values of the signal. The data channel must not contain NoValues and the values of the data channel must be strictly monotonic increasing and equidistant.
	Signal channels	Displays the data channels with the amplitude values of the signal. The data channels must not contain NoValues.
	Select Channels	Opens the channel selection list. You can select one or more channels.
	Generate index channel	Specifies whether DIAdem counts the number of FFTs in an index channel. This option is only available when DIAdem runs FFTs on several data channels or time intervals and does not average the amplitudes.
Window Functions
	Window type	Specifies the window function.
	Parameters of the window function	Specifies the parameters for parameter-related window functions.
	Channel	Specifies the data channel that contains the values of a user-defined window function.
	Amplitude attenuation correction	Specifies whether and how DIAdem corrects the damping effect of the window function on the amplitude.
FFT Functions
	Real/imaginary part	Specifies whether DIAdem calculates the real and imaginary parts.
	Phase	Specifies whether DIAdem calculates the phase spectrum.
	Cepstrum	Specifies whether DIAdem calculates the cepstrum. The cepstrum is the spectrum of the logarithmic spectrum of the signal.
	Amplitude	Specifies whether DIAdem calculates the amplitudes.
	Amplitude mode	Specifies the type of amplitude.
	Third/octave	Specifies whether DIAdem calculates third or octave analyses for the amplitudes.
	Average amplitudes	Specifies how DIAdem averages the amplitudes.
	Calculate average from	Specifies whether DIAdem calculates the average from the amplitudes or the autospectra.
Time Intervals
	User-defined parameters	Specifies which parameters the user defines and which are defined automatically.
	Number of intervals	Specifies the number of intervals for the data channel to be analyzed.
	Interval length	Specifies the length of the intervals. The interval length must be greater than 2
	Start	Specifies the start row in the data channel to be analyzed.
	Overlap (%)	Specifies the overlapping of the time intervals as a percentage of the interval length.
	NoValue Handling	Specifies how DIAdem handles intervals that contain NoValues. If you set this parameter, DIAdem searches for an interval with the specified length and calculates the FFT for the window. If you only specify one y-channel, or the interval length is not specified automatically, or the time channel has NoValues, the interval is searched for.

If you want to use waveform channels in this dialog box, follow Rule 2.2 for Calculating with Waveform Channels. The result channels with the frequency and the quefrency are not included. All other result channels, except the optional index channel, are waveform channels that have the frequency or the quefrency as the x-part.

Note  If you calculate the FFT across more than one time interval, DIAdem includes only the first signal pair. If you calculate the FFT with an odd number of values, the inverse FFT may show small deviations from the original values in the sampling frequency and the number of values.

Result

DIAdem generates at least two result channels. The first result channel contains the frequency. The other result channels contain the function values selected under FFT Functions.

Refer to the Help page Fourier Transform for further information.

To calculate quantity-based in DIAdem, click the Calculate Quantity-Based button on the DIAdem ANALYSIS toolbar. When executing quantity-based calculations, DIAdem checks whether the program can also execute calculations on physical quantities in the same calculation. If DIAdem cannot execute the calculation because the physical quantities are unsuitable, the program displays an error message. Refer to the Help page Calculating Quantity-Based and Non-Quantity-Based in DIAdem for the conditions and rules for quantity-based calculations.

Script Call

Call SUDDlgShow("Main", ResourceDrv & "AnaChnFFT1")

ChnFFT1

Procedures

Examining Measurement Signals in the Frequency Domain

Examples

AC/DC Coupling | Adapted DIAdem Functions | Calculate Characteristics of an Oscillation | Communicating with MATLAB | Frequency Weighting (A-, B-, C-Filtering) | Hysteresis Analysis | Optimized Heating Control