AI Start Trigger Signal
Use the Start Trigger signal to begin a measurement acquisition which consists of one or more
samples. Once the acquisition begins, configure the acquisition to stop in one of the following
ways:
• When a certain number of points has been 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 default delay from the start
trigger to the first sample.
Using a Digital Source
To use the Start Trigger signal with a digital source, specify a source and a rising or falling
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 cRIO controller. Refer to
the "Device Routing in MAX" topic in the NI-DAQmx Help or the LabVIEW Help for more
information.
Using an Analog Source
Some C Series 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 for Start
Trigger, the acquisition begins on the first rising edge of the Analog Comparison Event signal.
Routing AI Start Trigger to an Output Terminal
You can route the Start Trigger signal to any output PFI terminal. The output is an active high
pulse.
Using a Time Source
To use the Start Trigger signal with a time source, configure a specific time in NI-DAQmx.
Refer to the "Timestamps" and "Time Triggering" topics in the NI-DAQmx Help for more
information on accessing time-based features in the NI-DAQmx API.
AI Reference Trigger Signal
Use a reference trigger to stop a measurement acquisition. To use a reference trigger, specify a
buffer of finite size and a number of pretrigger samples (samples that occur before the
reference trigger). The number of posttrigger samples (samples that occur after the reference
trigger) desired is the buffer size minus the number of pretrigger samples.
50 | ni.com | cRIO-904x User Manual
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