Trigger

What it does

Trigger monitors one of your incoming waveforms and checks its behaviour against the conditions set within the trigger options. Once the monitored waveform meets those conditions a capture is triggered and your waveforms are stored and displayed. One typical set of trigger conditions, known as an edge trigger, is that the waveform amplitude must cross through a certain threshold value as it is heading in a particular direction (e.g. either rising or falling).

How it can help you

Without a trigger, your waveforms are captured and displayed as they arrive. This can make it hard to see rapidly changing waveforms as you cannot predict when and where they will appear on the screen. Trigger solves this problem by fixing a selected waveform feature (determined by the selected trigger options) at the 0 seconds time position, which causes the waveforms to appear in the same place and stabilize.

By carefully selecting the trigger waveform and options, you can check to see how the other waveforms change in response to the trigger waveform (or vice-versa) or to changes in the test conditions during correlation measurements.

Triggers also enable hands-free scope operation during:

• Wiggle-testing to expose intermittent shorts, open circuits or high resistances; the trigger can be set to capture the faulty waveform behaviour whilst the user manipulates the wiring harness to provoke the underlying fault.
• Tests involving cranking (such as relative compression) or turning the engine on or off. I.e. where the user needs to control the vehicle as part of the test conditions.

How to use it

Click the Trigger control to open the Trigger panel.

Select the Mode:

Auto trigger mode waits for a predetermined length of time before displaying data regardless of whether the trigger conditions have been met.

Repeat trigger mode captures and displays data every time the trigger conditions are met.

Single trigger mode captures and displays data on only the first occasion that the trigger conditions are met.

Select the Source (the trigger channel).

Select the Pre-trigger. The pre-trigger is specified as a percentage of your timebase. It determines where the 0 seconds point lies on your timebase and, therefore, where the waveform will appear on your screen.

The trigger type is displayed under Type. Click the Change type icon to change the trigger type. A Trigger type dialog will open and present a set of trigger icons. Each icon illustrates the important features associated with each trigger type. Click on a trigger icon to select the trigger type.

Under the displayed trigger type, in the Trigger panel, are the associated trigger options that you use to set the trigger conditions. For example, a Simple edge trigger type has controls that you can use to set the Threshold and Direction conditions.

When a trigger has been selected, a yellow diamond symbol is displayed on the graph to indicate the trigger threshold and pre-trigger. The symbol can be dragged across the graph area as a means to rapidly change these settings.