5.2 Trigger modes and time-stamps
56 Acqiris SA240P User's Manual
(2
24
– 1) *16/SamplingRate(in seconds
1
)
When using a reduced sampling rate, the decimation changes the SamplingRate to apply in
previous formulas.
Pre- or post-trigger delays are just different aspects of the same trigger positioning parameter:
The condition of 100% pre-trigger indicates that all data points are acquired prior to the trig-
ger, i.e. the trigger point is at the end of the acquired waveform.
The condition of 0% pre-trigger (which is identical to a post-trigger of 0%) indicates that all
data points are acquired immediately after the trigger, i.e. the trigger point is at the beginning
of the acquired waveform.
The condition of a non-zero post-trigger delay indicates that the data points are acquired after
the trigger occurs, at a time that corresponds to the post-trigger delay, i.e. the trigger point is
before the acquired waveform.
By definition post-trigger settings are a positive number and pre-trigger settings are a negative
number.
The trigger delay granularity is less than one sample interval (~ 0s).
Averager acquisition mode
In this mode the pre-trigger delay is not supported. Thus the minimum trigger delay is 0s.
The maximum trigger delay is given by:
(2
24
-1)*16/ SamplingRate
The trigger delay granularity is given by:
16 / SamplingRate
Trigger time interpolator and time-stamps
The trigger time-stamp is the trigger arrival time.
The ADC card accurately measures and stores these time-stamps using the information from the on
board Trigger Time Interpolator (TTI). This information is essential for determining the precise
relation between the trigger and the digitized samples of the signal. The TTI resolution determines
the resolution of the trigger time-stamps.
Please refer to Trigger section of your SA240P datasheet for the relevant specifications.
Managing time-stamps
The ADC card features a time-stamp counter. In multi-record acquisitions, each acquired record has
a precise time-stamp, given by the time-stamp counter.
The accurate time-stamp of each trigger is given by the sum of the time reference and the time-
stamp counter.
The time reference is configured:
1
Actual limit might be slightly smaller.
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