National Instruments Eight-slot USB Chassis NI cDAQ-9172 - Manual (Page 21)

© National Instruments Corporation 21 NI cDAQ-9172 User Guide and Specifications
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 Signal
Use 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
The source also can be one of several other internal signals on your
NI cDAQ-9172 chassis. Refer to the Device Routing in MAX topic in the
NI-DAQmx Help or the LabVIEW Help in version 8.0 or later for more
information.
The NI-DAQmx Help is available after installation from Start»
All Programs»National Instruments»NI-DAQ»NI-DAQmx Help.
To view the LabVIEW Help, in version 8.0 or later, select Help»
Search the LabVIEW Help in LabVIEW. Alternately, to download
the LabVIEW Help, go to
ni.com/manuals .
You also can specify whether the measurement acquisition begins on the
rising edge or falling edge of ai/StartTrigger.