Pre trigger / Pre samples

With digital storage oscilloscopes, the record length determines the number of samples that are measured. All these samples can be measured after the trigger has occurred. It is however possible to measure (a part of) the record before the trigger occurs, by selecting pre samples.

Pre and post samples

The total record will then be divided in a pre trigger part and a post trigger part, respectively containing pre samples and post samples. This way it is possible to "look back in time" since the pre samples were captured before the trigger moment.

With the TiePie engineering instruments it's possible to define the trigger moment at any position in the record.

Changing the trigger moment in the Multi Channel oscilloscope software can be done in various different ways:

  • By right-clicking the instrument in the Object Tree, selecting Pre trigger and then the appropriate pre trigger percentage in the popup menu.
  • By using hotkeys SHIFT + ← and SHIFT + →.
  • By using the pre samples turning knob Presamples knob on the instrument toolbar.
  • By clicking the increase/decrease pre trigger percentage buttons Decrease presamples and Increase presamples on the instrument toolbar.
  • By right-clicking the horizontal scrollbar under the graph displaying signals from the instrument and selecting Pre trigger and then the appropriate pre trigger percentage in the popup menu.
  • By dragging the small triangle on the slider in the horizontal scrollbar under the graph displaying signals from the instrument left or right. The position of the triangle in the scrollbar represents the trigger moment in the measured record.

When setting the trigger moment through a popup menu, the option User defined... also allows to set the value as a number of samples or as a time.