Difference between revisions of "NVGate FFT"

Use: [[NVGate_Software_overview#GoToResult|GoToResult]]

Diplay windows can be done in 2 ways.

[[Image:FFT_05.png|framed|none]]

There are sevral ways to access the settings :

We advice the first one.

Contains the settings related to the source input.

* '''Weighting window''': window used to weighting the signal before the processing. There are six set windows: Uniform, Hanning, Hamming, Kaiser Bessel, Flat top, and three customized windows: Force, Response and Dual exp (see the Time Windows chapter). For the window characteristics, see the Appendix.

Contains the settings related to trigger events and how to start, and stop signal computation.

''Hidden/fixed: The Trigger frequency is enabled when FFTx/Average/Domain is set to Frequency Synchronous.''

Contains the settings related to the type of averaging of the signals to be computed.

* '''Reference channel''': channel to be used as a reference in the Referenced Peak hold averaging mode. This setting is only available when this averaging mode is selected. You can choose between the channels that are plugged into the FFT plug-in, if <nowiki>’</nowiki>None<nowiki>’</nowiki> is selected the average processing is the same as the Peak hold mode.

Contains the settings related to the type of analysis of the signals to be computed.

* '''Autobandwidth''': manages the analysis and recording bandwidths automatically. The ''Inputs selection'' window '''allows the use of 2 different sampling rates for the dynamic inputs'''. It gathers inputs with the same physical quantity into groups, maintaining the same sampling into each group. When inputs are associated with '''the analysis plug-in, it adjusts its analysis bandwidth to match the inputs ones'''. Mixing input bandwidths in one analysis plug-in lead to set its bandwidth to the lowest one. ''Autobandwidth'' is set by default in the FFT plug-ins.  it adjusts the setting :  FFT Analysis\Range .When it is enabled in the plug-in, these settings "switch to informative status"

Unlike the display zoom function; the analysis zoom function allows you to zoom into a selected bandwidth increasing the analysis resolution.

* Set '''Factor''' and '''Center''' (min and max values are update automatically with the center frequency) if the zoom would be done around a central frequency well defined. By modifying Factor, max and min frequencies will be automatically set to define zoom limits.

* Set '''max''' and '''min''' frequencies (center and factor are update automatically) if the limits in frequency would be fixed on specific values.

[[NVGate_Envelope_analysis|Read the user note for more info about envelope analysis.]]

[[category:FFT]]

Contains the settings related to constant band tracking operations.

[[NVGate_CBT_principle_and_settings|Read the dedicated CBT page for more info.]]

'''Note''': This set up don<nowiki>’</nowiki>t change the spectrum phases and consequently don<nowiki>’</nowiki>t change the orders phases extracted from a waterfall of spectra.

Calculation of the Auto Correlation and the Cross Correlation.

[[File:Correlation2.png|left]]<br>

* Use appropriate trigger mode and trigger delay. The trigger mode should be different from free run. The trigger Delay must be set to –T/2 (where T is the time signal block length) with the Uniform and Centered Zero Padding correlation weighted window (and 0 for the Left Zero Padding window). But in some cases, especially with the Centered Zero Padding and Left Zero Padding window (as these function types attenuate parts of the trigger signal block), the trigger Delay must be adjusted to position the input signal with respect to time.

Calculation of the FFT bands sum.

* '''Upper frequency''': Specifies the upper frequency of the overall computation frequency range.

All status are available for the control panel. Statuses are refreshed all the time at roughly 10 Hz.

In structural mode, a state <nowiki>’</nowiki>Waiting<nowiki>’</nowiki> is available and is waiting for the <nowiki>’</nowiki>Accept/Reject<nowiki>’</nowiki> event to continue.

This status displays the averaging count processed. This status is expressed in analyzed block.

This status displays if the averaging is in real-time or not (i.e. the current block is analyzed or not). If the corresponding signal were not available at this time, the acquisition is not real-time. That means that the treatment is longer than the acquisition. There are three values for this state:

* '''<nowiki>’</nowiki>-<nowiki>’</nowiki>''': The acquisition is currently not real-time (current block is not analyzed an averaged).

This status corresponds to the instantaneous overload indication within 1 FFT trigger block, for instance amplitude overload occurred in the current analyzed block. It is useful in structural mode if for one hammer impact one channel is overloaded. Note that overloaded block may be automatically rejected (see accept mode).

This status corresponds to overload indication over the measurement period. It means that during the whole measurement period there was (or not) an overload. It memorizes block overloaded.