Ai Start Trigger Signal; Using A Digital Source; Using An Analog Source; Routing Ai Start Trigger To An Output Terminal - National Instruments NI cDAQ-9181 User Manual

AI Start Trigger Signal

Use the Start Trigger 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 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 cDAQ chassis. 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.
Depending on the C Series module capabilities, you may need two modules
Note
to utilize analog triggering.

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.

AI Reference Trigger Signal

Use 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.
NI cDAQ-9181/9184/9188/9191 User Manual
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