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Triggering

Click the Options | Processing Settings menu and click on the Triggering tab or click the trigger toolbar button.  

When triggering is enabled, the processor will test the current data block for a trigger condition before performing an FFT.  

Trigger Mode: Controls the behavior of the analyzer after a trigger event occurs:
  • Rearm and wait for next trigger - the analyzer will pause and continue to examine the incoming data stream for the presence of a trigger condition.  This is the default behavior.  
  • Stop the analyzer - the analyzer will stop after the first trigger has been detected and processed.
  • Continue running or recording - the analyzer will continue to run normally after the first trigger condition has been detected and processed.  If the analyzer is stopped and restarted, it will once again wait for another trigger event.

    Trigger Channel: controls which input channel to check for a trigger event.

    Trigger Type:
  • Level triggering - the analyzer will test the current data block for a time series data value which exceeds the specified threshold.
  • Edge triggering - the analyzer will test  the current data block for a sharp transition (difference in level between any two samples exceeds the threshold setting).  This is useful for triggering on pulse type signals.  

    Trigger Polarity: controls whether the trigger threshold is a positive or negative value.

    Threshold: Sets the trigger threshold. The threshold units correspond to the current calibration units.  Note: You can also set the threshold by right clicking on the Time Series plot.

    Trigger Delay/Type: can be used to adjust the acquisition window within the FFT block.  Pre-delay will move the trigger point to the right, post-delay to the left.  If the delay is set to zero, the trigger point is positioned at the start of the FFT data block.  The delay value can be specified in milliseconds or as a percent of the FFT size.

    Prompt User to Accept/Reject Trigger Waveform - if enabled the trigger waveform will be displayed and the user will be prompted to accept or reject the trigger event from being included in the spectral average.  This is helpful for impact hammer testing to exclude double strkes from the measurement.  The smoothing window will be applied to the displayed waveform.

    Start signal generator on initial trigger event - this will delay the start of the signal generator until the first trigger event is detected.  The signal generator utility must be open when the analyzer is started for this option to take effect.  Please note that due to operating system latencies the exact time between the trigger event and the start of the generator cannot be precisely controlled.

    Notes:
    External triggering can be performed by utilizing one of the channels for data and the other for the trigger pulse.  Select the appropriate trigger channel in the trigger dialog box and then setup the analyzer to only display the spectrum of the data channel.

    Caution!
    When triggering is enabled, the processor may appear not to work if the signal stays below the threshold.  Check the status bar along the bottom edge of the program for the current mode.