Long Time Waveforms Explained
Long time waveforms allow you to take a continuous recording over a very long time period (many hours, if required), making it particularly useful for capturing transients. Once measuring has begun, recordings are taken continuously until your specified time period has elapsed or you manually stop the measurement. The amount of time you can record for depends on the Equivalent Fmax (which determines the sample rate/lines of resolution) and how much available memory is left in the instrument.
Measuring Long Time Waveforms
Note: This feature is not available on the vb5 or vb6 instrument models.
Duration is the total amount of time available for recording and is displayed in seconds. You can record for the full length of time available or set a shorter time period. Your chosen time period is shown on top, while the available time is shown in brackets below this value.
The Equivalent Fmax (which determines the maximum frequency displayed on-screen) will affect the available recording time; a high Fmax reduces recording time, while a low Fmax increases the total amount of time available for recording.
While the instrument is recording you can display the on-screen signal as a waveform, or convert it to a spectral display by pressing Display Type & Resolution and selecting your preferred display type.
- From the Main Menu press
Measure then use the left-hand arrow keys to highlight Long Time Waveform and press 
. - Use the left-hand arrow keys to select a parameter set or press
to create a new one and set the parameters as required. - Press to begin measuring. During measuring the number at the top of the screen indicates how many recordings have been taken. The default onscreen display during measurement will show spectrum and waveform simultaneously.
- When measuring is complete the screen will display a waveform 'block' (or spectrum if you selected this option) and a trend of the overall power in the last recording. To view the power in another recording use the right-hand arrows to move the cursor.
- The top chart can also display a trend of the machine speed if you used a speed sensor. To toggle between overall power and RPM press
.
When measuring is finished the selected measurement location will contain many individual recordings.
When the waveforms are later transferred to the software and displayed as spectra, the equivalent Fmax value will be used on the chart (the actual sampling rate is 2.56 times higher than this Fmax
value).
Viewing Long Time Waveforms on Your PC
When you have finished recording, the selected measurement location will contain many individual 4096 sample recordings. After transferring these to your PC you can then use the waveform analysis tools to create a high resolution spectrum of the recordings by selecting Analyze>Partial Waveform Analysis or Freq. Based Waveform Analysis (refer to your Ascent Software Reference Guide for full instructions).
Last Reviewed: 11/Jun/2009 Source: vbSeries Reference Guide Revision 24 Mar 2009 - pages 78 -80