Measurement Computing Data Translation DT9857, Руководство пользователя

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Chapter 5
80
Figure 33 illustrates continuous scan mode (using a start and reference trigger) with a channel
list of three entries: channel 0 through channel 2. In this example, pre-trigger analog input
data is acquired when the start trigger is detected. When the reference trigger occurs, the
specified number of post-trigger samples (three, in this example) are acquired.
Figure 33: Continuous Scan Mode on the DT9857 and DT9857E Modules
Using a Start and Reference Trigger
Note: The Input Trigger LED on the module, shown on page 176 , is amber to indicate an
armed condition when the module is waiting for an external digital trigger, threshold trigger,
or Sync Bus trigger (the module must have been configured for one of these trigger types),
green when the module has been triggered, or off when the module is idle.
Input Triggers
A trigger is an event that occurs based on a specified set of conditions.
If you are using continuous scan mode, described on page 79 , you must specify a start trigger
to start acquisition. If you want to acquire pre-trigger and post-trigger data, you must also
specify a reference trigger. In this case, pre-trigger data is acquired when the start trigger
occurs. When the reference trigger occurs, pre-trigger acquisition stops and post-trigger
acquisition starts. The operation continues until the number of scans that you specify for the
post-trigger scan count are acquired; at the point, the operation stops.
The following sections describe the start and reference trigger sources that you can configure.
Chan 0
Chan 1
Chan 2
Input
Sample
Clock
Chan 0
Chan 1
Chan 2
Chan 0
Chan 1
Chan 2
Chan 0
Chan 1
Chan 2
Start Trigger occurs Reference Trigger occurs
3 Post-trigger samples acquired
Pre-trigger data acquired
Chan 0
Chan 1
Chan 2
Post-Trigger Scan Count = 3
Chan 0
Chan 1
Chan 2
Trigger Sample is not counted
as post-trigger sample