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AI Sample Clock Signal

    Last Modified: May 20, 2019

    A sample consists of one reading from each channel in the AI task. Sample Clock signals the start of a sample of all analog input channels in the task. Refer to the following figure for sample clock source options.

    Figure 1. AI Sample Clock Timing Options

    The FD-116xx is considered a Delta-Sigma device; it contains multiple A/D converters that require a high-frequency oversample clock to produce accurate, synchronized data. The FieldDAQ device returns a sample on every Sample Clock pulse.

    The oversample clock is used as the AI Sample Clock Timebase. The FieldDAQ device supplies 13.1072 MHz, 12.8 MHz, 12.288 MHz, and 10.24 MHz timebases. By default,NI-DAQmx automatically chooses the most suitable timebase for a selected data rate.[1]

    The FieldDAQ device automatically issues a synchronization pulse to each bank that resets their ADCs at the same time. You can also specify a specific time for the synchronization pulse to occur. Because of the filtering used in the Delta-Sigma FieldDAQ device A/D converters, these devices exhibit a fixed input delay relative to non-Delta-Sigma devices in the system. This input delay is specified in the FD-116xx Specifications.

    When using multiple FieldDAQ devices in a task that contains channels for a Delta-Sigma device, such as the FD-116xx, ensure that one of those channels is the first in your channel list.

    • 1 Automatic timebase coercion is supported in NI-DAQmx 18.5 and later. Previous versions of NI-DAQmx use the 12.8 MHz timebase by default.

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