Getting The Most Out Of Your Oscilloscope: Trigger Delay

Figure 1: Pre-triggering, or trigger delay, is a useful tool for
debugging applications

Triggering is one of the most basic, yet most useful, tools your oscilloscope offers you. Say you want to see what led up to, and/or what follows, a trigger condition. You're looking at an interesting waveform such as that shown in Figure 1. You have the trigger's delay position set at 10% and 90%.

But now you want to change the horizontal time base setting, and when you do, that trigger delay position changes along with the time/div setting. You want that trigger delay position to stay put. What's the fix for this situation?

On Teledyne LeCroy oscilloscopes, it's pretty easy. Open the Utilities dropdown menu, select Preference Setup, and then select the Acquisition tab in the dialog box. In the center of that tab is "Delay Setting Constant In:" with options of Time or Div (divisions). That's where you can set the trigger delay point to be constant in terms of either the horizontal divisions on the grid or in absolute time. So you can make the center of the screen the reference point for a time base change, or you can

Figure 2: Utilities > Preference Setup > Acquisition takes you
to this dialog, where you can set trigger delay (and vertical
voltage sensitivity) to a constant position

have that trigger delay point stay put wherever you'd initially placed it, referencing time base changes to that arbitrary point.

Meanwhile, on the left side of the same tab is the section headed "Offset Setting Constant In:" with options being Volts or Div. It's the same idea as the horizontal setting, but now it's for the vertical axis, enabling you to choose between volts or absolute volts. Changing that setting to Div means that ground will be the reference point for all vertical sensitivity changes independent of where the offset marker is.

Previous posts in this series:
Getting The Most Out Of Your Oscilloscope: Setup
Getting The Most Out Of Your Oscilloscope: Navigation with MAUI