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AI Start Trigger Signal

    Last Modified: August 30, 2018

    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 Timestamps and Time Triggering in the NI-DAQmx Help for more information on accessing time-based features in the NI-DAQmx API.

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