© National Instruments Corporation 13 NI cDAQ-9172 User Guide and Specifications
The NI cDAQ-9172 has one AI timing engine, which means that only
one analog input task may be running at a time on a chassis. However, the
analog input task can include channels from multiple analog input modules.
Analog Input TriggeringA trigger is a signal that causes an action, such as starting or stopping the
acquisition of data. When you configure a trigger, you must decide how
you want to produce the trigger and the action you want the trigger to cause.
The NI cDAQ-9172 chassis supports internal software triggering, external
digital, and analog triggering.
Three triggers are available: start trigger, reference trigger, and pause
trigger. An analog or digital trigger can initiate these three trigger actions.
Any C Series correlated digital input module can supply a digital trigger
when installed in slots 5 or 6, and some C Series analog modules can supply
an analog or digital trigger in any slot. The start, reference, and pause
triggers can come from three separate modules if desired. To find your
module triggering options, refer to the documentation included with your
C Series I/O modules. For more information about using digital modules
for triggering, refer to the Digital I/O section.
AI Start Trigger SignalUse the AI Start Trigger (ai/StartTrigger) signal to begin a measurement
acquisition. A measurement acquisition consists of one or more samples. If
you do not use triggers, begin a measurement with a software command.
Once the acquisition begins, configure the acquisition to stop in one of the
following ways:
• When a certain number of points is sampled (in finite mode)
• After a hardware reference trigger (in finite mode)
• With a software command (in continuous mode)
An acquisition that uses a start trigger (but not a reference trigger) is
sometimes referred to as a posttriggered acquisition. That is, samples are
measured only after the trigger.
When you are using an internal sample clock, you can specify a delay from
the start trigger to the first sample.
Using a Digital Source
To use ai/StartTrigger with a digital source, specify a source and an edge.
Use the following signals as the source:
•Any PFI terminal
• Counter n Internal Output