Hello everyone, sometimes we encounter such waveforms in waveform measurement. Based on the characteristics of the waveform, we have set the appropriate edge trigger, but the waveform still cannot be displayed stably. What is the reason for this? How should we operate in this case?
In the trigger settings, there is a function to set the trigger hold-off time. The hold-off time refers to the time the oscilloscope waits to re-enable the trigger circuit. During the hold-off period, the trigger circuit is closed, and the triggering function is paused. Even if there are waveforms that meet the trigger conditions during the hold-off time, the oscilloscope will not trigger.
The trigger hold-off function is specifically designed for large periodic repetitions where there are many non-repeating waveform points that meet the trigger conditions within a large period. If the hold-off function is not used, the trigger point will not be fixed, which can cause unstable display. After the oscilloscope uses the trigger hold-off function, it must wait for the hold-off (Hold Off) time after the first trigger before it can trigger a second time. In the figure, the hold-off time can be set to >200 ns but <600 ns. By using the trigger hold-off, it triggers at the same point each time, thus allowing for stable display.
Figure 1: Trigger Hold-Off Time
We press the [Trigger] button, and in the trigger settings menu, we can set the trigger hold-off time. Turn knob A for fine adjustment, and turn knob B for coarse adjustment. Generally, the hold-off time should be set to slightly longer than one cycle, but it cannot enter the next cycle. Observing the screen waveform, we can see that we only need to set the trigger hold-off time slightly greater than 4us, but it cannot exceed one cycle.
Figure 2: Screen Waveform
It should be noted that the trigger hold-off time is not the same as the dead time. The purpose of setting the trigger hold-off time is to increase the dead time to stably capture and display some special signals.