Asynchronous/ Synchronous Triggering Versus Record Time; Example - Texas Instruments CBL 2 Reference Manual

Asynchronous/ Synchronous Triggering versus Record Time

Actual triggering is asynchronous from the internal sampling clock when Trigger Type
in Command 3 is set to 1 or 6 (manual triggering). If sampling at very fast rates, the
actual trigger may be slightly different from the commanded trigger. The user should
take this into account when calculating prestore and trigger levels.
The actual sample time for the trigger point depends on whether or not prestore is
selected in Command 3.
When prestore and relative record time are selected, the sample time for the trigger
point will generally not be identical to times around it. The time recorded for the
trigger point will be the actual time between the previous sampled point on the
internal sampling clock interval and the asynchronous trigger event. The sample taken
after the trigger point will be at the specified sample time since the clock is reset each
time the trigger event occurs (pressing START/STOP or the hardware threshold trigger
event).
When Trigger Type is set to 6 (Manual and Sample Trigger) in Command 3, the
recorded sample times are the actual relative times when START/STOP is pressed.
When no prestore is selected, the first sample time will be the trigger point. Its
recorded time will not be the internal sample clock time because the CBL 2 is always
sampling on the internal clock interval that you selected and is storing points (if you
selected prestore) until the trigger event occurs.

Example

Assume the following:
Input to CH1, set to measure ±10 Volts, is a 0.01 Hz sine wave.
Sample Time is set to 10 seconds and Number of Samples is set to collect 30 points.
Trigger Channel is set to 1.
Trigger Threshold is set to 1.0 and Trigger Type is set to 2 (trigger on rising edge).
The CBL 2 will collect and store a sample every 10 seconds. The recorded time for each
sample will be 10 seconds. The trigger event (signal rising through 1.0 Volts) occurs 1.5
seconds after the previous sample, so a sample collected at the trigger point is taken
and stored with a recorded time of 1.5. The next sample is taken 10 seconds after the
trigger sample, not 8.5 seconds later as would have happened if the internal sample
clock had not been reset.
The Record Time returned (around the trigger point) will be the list:
{...10,10,10,1.5,10,10,...}.
CBL 2 Technical Reference 21