User Guide

© National Instruments Corporation 23 NI cDAQ-9172 User Guide and Specifications
When the reference trigger occurs, the NI cDAQ-9172 continues to write
samples to the buffer until the buffer contains the number of posttrigger
samples desired. Figure 9 shows the final buffer.
Figure 9. Reference Trigger Final Buffer
Using a Digital Source
To use ai/ReferenceTrigger with a digital source, specify a source and an
edge. Either PFI or one of several internal signals on the NI cDAQ-9172
chassis can provide the source. 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 stops on the
rising edge or falling edge of ai/ReferenceTrigger.
Using an Analog Source
Some C Series I/O modules can generate a trigger based on an analog
signal. In NI-DAQmx, this is called the Analog Comparison Event.
When you use an analog trigger source, the acquisition stops on the first
rising or falling edge of the Analog Comparison Event signal, depending
on the trigger properties.
Routing AI Reference Trigger Signal to an Output Terminal
You can route ai/ReferenceTrigger to any output PFI terminal.
Reference Trigger
Pretrigger Samples
Complete Buffer
Posttrigger Samples