Measurement Computing WaveBook rev.5.3 - Manual (Page 89)

Falling-Edge Trigger
Falling slope
Instantaneous duration
Edge initialization
Hysteresis
Trigger
Trigger Level
No Trigger
This trigger is the reverse of the rising-edge trigger: the trigger becomes valid after the signal level has
been above the hysteresis range and then goes below the trigger level. This trigger becomes invalid
whenever the signal level goes above the hysteresis range. This prevents the false triggering that would
occur with below-level triggering if the signal was below the trigger level at the start of the acquisition.
Rising-Edge-With-Latch Trigger
Rising slope
Latched duration
Edge initialization
Trigger Level
Hysteresis
Trigger
This trigger becomes valid like a rising-edge trigger: when the signal level goes above the trigger level
after first being below the trigger range. However, the rising-edge-with-latch trigger does not become
invalid, regardless of the signal level, until the acquisition is complete. Rising-edge-with-latch is used to
trigger after the channel has reached the trigger level, rather than just while the channel is above the trigger
level.
Falling-Edge-With-Latch Trigger
Falling slope
Latched duration
Edge initialization
Trigger Level
Hysteresis
Trigger
This trigger is the reverse of the rising-edge-with-latch trigger: the trigger becomes valid after the signal
level has been above the hysteresis range and then goes below the trigger level. The trigger remains valid
until the acquisition is complete.
Trigger Latency & Jitter
Trigger latency and jitter depend on the trigger source and the acquisition mode:
Trigger latency is the duration between the valid trigger and the start of the acquisition.
Trigger jitter is the variation of the latency, how much time the latency can vary from trigger to
trigger.
As discussed, WaveBook has post-trigger and pre/post-trigger acquisition modes. Post-trigger modes
(N-shot, N-shot with re-arm, and infinite-post-trigger) collect scans only after the trigger has occurred.
They are different from the pre/post-trigger mode that collects scans both before and after the trigger.
This difference affects the trigger latency and jitter.
In a post-trigger mode, WaveBook is not scanning while waiting for the trigger. Thus, it is free to respond
to the trigger as soon as it occurs. This minimizes the trigger latency and jitter.
In the pre/post-trigger mode, pre-trigger data is being collected while WaveBook waits for the trigger, and
WaveBook will not respond to a trigger, until after the current scan is complete. The pre-trigger scan
period separates the first scan after the trigger from the last scan before the trigger. All the scans (up
through the one immediately following the trigger) are collected at the pre-trigger rate; and all subsequent
scans are collected at the post-trigger rate. This preserves the integrity of the acquisition timebase as
shown in the figure below:
Start
No acquisitions
before start
Pre-Trigger
Scan Period
Pre-Trigger Scan Count
Pre/Post-Trigger Acquisition
Time
Trigger
Armed
Trigger
Pre-Trigger
Scan Period
Post-Trigger
Scan Period
Post-Trigger Scan Count
WaveBook/512A, /516, /516A , /516E 897895 WaveBook Operation Reference 4-19