User Guide

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.