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[[category:FFT]] | [[category:FFT]] | ||
=====Order analysis===== | |||
Contains the settings related to constant band tracking operations. | |||
[[Image:Order_analysis_03.png|framed|none]] | |||
* '''Associated tach''': The selected Tach enables the FFT plug-in to perform Constant Band Tracking. | |||
'''Warning''': Do not select an associated tach if you do not use one, the FFT will not start. | |||
* '''Center on peak''': This setting is used to center the spectral lines used to compute the total power around a peak (if it exists) close to the order frequency. | |||
* '''Refresh mode''': When displaying some order profile results, this setting is used to choose between two methods of adding a new measurement point to the curve. | |||
* | |||
{|border="2" cellspacing="0" cellpadding="4" width="92%" align="center" | |||
|'''Mode''' | |||
|'''Description''' | |||
|- | |||
|Delta time | |||
|A new point is added periodically. The Time Resolution settings set the refreshing period. | |||
|- | |||
|Delta RPM | |||
|A new point is added each time the Tach speed has increased the Speed Resolution setting value. | |||
|}<br clear="all"> | |||
* '''Duration profile''': The size of the profile window time axis. | |||
* '''Time resolution''': used to set the refreshing period for the order profile results. This setting is visible if the Refresh Mode setting value is Delta time. | |||
* '''Max speed''': The Max speed that the Tach selected with the Associated Tach setting can handle. This value is for information only; it cannot be set directly. This setting is visible if the Refresh Mode setting value is Delta RPM. | |||
* '''Min speed''': The Min speed that the Tach selected with the Associated Tach setting can handle. This value is for information only; it cannot be set directly. This setting is visible if the Refresh Mode setting value is Delta RPM. | |||
* '''Speed resolution''': used to set the refreshing conditions for the order profile results. A new point is added each time the Tach speed has increased of the setting value. This setting is visible if the Refresh Mode setting value is Delta RPM. | |||
* '''Orders Phase ref''': This function allows to use the cross-spectrum phase value for the phase of the order (relative phase). The cross-spectrum phase is the relative phase between the input signal of the current channel and the reference input signal associated to this channel. Whatever the average mode, the average cross-spectrum is always used to calculate the orders phase. | |||
[[Image:Order_analysis_04.png|framed|none]] | |||
'''- Not activated''': The phase of the order is the spectrum phase of the frequency corresponding to the order value (absolute phase). If the average mode is spectral, the inst-spectrum is used and if the average mode is time, the average spectrum is used. | |||
- '''Activated''': choose the channel used to calculate the orders phase. | |||
If a channel is selected, the cross-spectrum matrix is not available anymore. | |||
'''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. | |||
=====Correlation===== | |||
Calculation of the Auto Correlation and the Cross Correlation. | |||
The cross-correlation function | |||
[[Image:Order_analysis_05.gif|framed|none]] | |||
gives a measure of the extent to which two signals correlate with each other as a function of the time displacement | |||
[[Image:Order_analysis_06.gif|framed|none]] | |||
between them. | |||
[[Image:Order_analysis_07_150.png|framed|none]] | |||
Where: | |||
[[Image:Order_analysis_08.gif|framed|none]] | |||
is the time displacement, | |||
[[Image:Order_analysis_09.gif|framed|none]] | |||
is the convolution symbol | |||
The auto-correlation is a special case where | |||
[[Image:Order_analysis_10.gif|framed|none]] | |||
. | |||
* '''Correlation: '''Allows to activate or not the calculation of the correlation. | |||
All results of the correlation are in the time domain with –T/2 et T/2 where T equal to the duration of the block trigger of the FFT. | |||
* '''Weighting window: '''Choose between following values of this setting: | |||
Three types of correlation window are available: | |||
'''Uniform '''<nowiki>[</nowiki>-T/2, T/2<nowiki>]</nowiki> (where T is the trigger block length): All the window coefficients are equal to 1. For best results with the Uniform weight window, you should use signal sources that are self-windowing, such as transients, burst, and periodic waveforms (signal period must be a multiple of the weight window length). In order to have the trigger point (T0) at the center of the time trigger block, the trigger Delay must be set to –T/2'''.''' | |||
[[Image:Order_analysis_11.png|framed|none]] | |||
'''Centered Zero Padding '''<nowiki>[</nowiki>-T/4, T/4<nowiki>]</nowiki> (where T is the trigger block length): Only the central part of the window (representing the half-length) is not null. This weight window must be used with random noise. In order to have the trigger point (T0) at the center of the time trigger block, '''the trigger Delay must be set to –T/4 '''(where T is the trigger block length) | |||
<font color="#FF00FF"> | |||
[[Image:Order_analysis_12.png|framed|none]] | |||
</font> | |||
'''Left Zero Padding''' <nowiki>[</nowiki>0, T/2<nowiki>]</nowiki> (where T is the trigger block length): Only the first half of the window is not null. This weight window must be used with random noise. In order to have the trigger point (T0) at the beginning of the time trigger block, '''the trigger Delay must be set to 0.''' | |||
<font color="#FF00FF"> | |||
[[Image:Order_analysis_13.png|framed|none]] | |||
</font> | |||
If the correlation is activated then all results of the FFT will be affected by the weighting windows of the correlation. When the setting Correlation is deactivated the weighting windows by default (Hanning) is applied on all inputs of the FFT plug-in. | |||
Notes: Results from the correlation are normalized. | |||
'''Considerations to obtain good results when making correlation measurement.''' | |||
* Use input '''AC '''coupling. Both auto correlation and cross correlation are disturbed by DC offset in the input signal. | |||
* 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. | |||
=====Overall analysis===== | |||
Calculation of the FFT bands sum. | |||
* '''Band power tracking''': Switches computation of the overall level result on or off. | |||
* '''Lower frequency''': Specifies the lower frequency of the overall computation frequency range. | |||
* '''Upper frequency''': Specifies the upper frequency of the overall computation frequency range. | |||
=====FFT status===== | |||
All statuses are available for the control panel. Statuses are refreshed all the time at roughly 10 Hz. | |||
[[Image:Order_analysis_14.png|framed|none]] | |||
The current plug-in status is synthesized in a special progress-bar. This progress bar is automatically displayed in the <nowiki>’</nowiki>control panel<nowiki>’</nowiki> when the plug-in is active (i.e. as soon as at least 1 input is connected to the FFT plug-in). This status is called <nowiki>’</nowiki>FFTx<nowiki>’</nowiki> (x from 1 to 4) and it is available in the status ASB tree (see customize control panel). | |||
This status displays the averaging count (i.e. current analyzed block number), the plug-in state and the real-time status. | |||
* '''State''': block number analyzed | |||
* '''Run:''' The FFT plug-in is computing spectra and averaging it. | |||
* '''Stop:''' The FFT plug-in is stopped. | |||
* '''Trig:''' The FFT plug-in is waiting for next block; i.e. next trigger event (block triggering) or first start event (triggering) | |||
* '''Pause: '''The FFT plug-in averaging is paused | |||
* '''Waiting:''' The FFT plug-in averaging is waiting for the acquisition to be accepted or rejected (in structural mode). | |||
'''Notes''': in exponential averaging mode the average counts stops increasing as soon as the set value is reached. | |||
The way the status bar is displayed, depends on the type of averaging selected: | |||
* '''<nowiki>’</nowiki>Linear<nowiki>’</nowiki>''', '''<nowiki>’</nowiki>Peak hold<nowiki>’</nowiki> '''or '''<nowiki>’</nowiki>Ref peak hold<nowiki>’</nowiki>: '''the progress bar is filled from left to right. | |||
* '''<nowiki>’</nowiki>Exponential<nowiki>’</nowiki>''': the progress bar is filled from right to left with a flashing until the end of the acquisition. | |||
The color of the background bar and of the text depends on real-time status: | |||
* ''Green background and white or black text'': acquisition in real-time. | |||
* ''Red background and white or black text'': the current acquisition is not real-time (current block is not analyzed). | |||
* ''Green background and red text'': the current acquisition is real-time, but since start not all the blocks were analyzed. | |||
[[Image:Order_analysis_15.png|framed|none]] | |||
This status displays if the measurement has been triggered (for long time acquisition) and the progression in the block. | |||
* Triggering: displays the state of the triggering in percentage before acquiring. | |||
* Acquiring: displays the progression of the time block acquisition in percentage. Until the acquiring period is not finished, the corresponding results are not available; they will be displayed at the end of the acquisition. | |||
[[Image:Order_analysis_16.png|framed|none]] | |||
* Paused: the acquisition is paused | |||
* Stop: the acquisition is stopped | |||
Trigger State | |||
The following scheme describes the basic statuses evolution of the FFT measurement: | |||
[[Image:Order_analysis_17.png|framed|none]] | |||
By default the trigger state is on <nowiki>’</nowiki>Stop<nowiki>’</nowiki> and waiting for a <nowiki>’</nowiki>Run<nowiki>’</nowiki> (start or trigger). Then the state become <nowiki>’</nowiki>Triggering<nowiki>’</nowiki> and is waiting for a start event, the states become <nowiki>’</nowiki>Block Triggering<nowiki>’</nowiki> and is now waiting for a trigger event for being in the <nowiki>’</nowiki>Running state. If there is less than one second elapsed since the end of current block analysis, FFT status stay at "running" state. | |||
The status is <nowiki>’</nowiki>Stop<nowiki>’</nowiki> after a stop event or at the end of averaging. | |||
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. | |||
======Count====== | |||
This status displays the averaging count processed. This status is expressed in analyzed block. | |||
======Real-time====== | |||
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>OK<nowiki>’</nowiki>''': The acquisition is real-time (all block have been processed and averaged) | |||
* '''<nowiki>’</nowiki>No<nowiki>’</nowiki>''': Acquisition was not real-time (some previous blocks are missing in the average). | |||
* '''<nowiki>’</nowiki>-<nowiki>’</nowiki>''': The acquisition is currently not real-time (current block is not analyzed an averaged). | |||
======Block overload====== | |||
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). | |||
======Analysis overload====== | |||
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. | |||