FieldDAQ devices feature automatic network-based synchronization with compatible networks and IEEE 802.1AS-capable NI Linux Real-Time controllers.

The SYNC logo on the device front panel indicates that the device is capable of hardware-based synchronization over a network.

FieldDAQ devices can be daisy-chained together or connected to external networks that support IEEE 802.1AS synchronization, and all device timebases will be automatically synchronized. Refer to Synchronization across a Network for more information about supported topologies and other technical requirements.

Network-synchronized devices can also take advantage of time-based synchronization features in NI-DAQmx. Certain triggers can be specified in terms of time of day. Time-based triggers and multidevice tasks (spanning multiple network-synchronized FieldDAQ devices) can help simplify programming for large systems.

Time triggers can be specified in Host Time or I/O Device Time, depending on the needs of your application.

  • I/O Device Time—The time the FieldDAQ device uses internally. This time is determined by the network configuration and is shared by all IEEE 802.1AS network-synchronized devices on your subnet.
  • Host Time—The time on your Windows computer or NI Linux Real-Time controller. This is usually the current global time and is provided by a local real-time clock or a network time protocol (NTP) server.

    • NI-DAQmx automatically translates from Host Time to I/O Device Time as necessary. The accuracy of this translation depends on the relationship between these times and can reduce the relative accuracy of time triggers across multiple devices. For maximum accuracy, use an NI Linux Real-Time controller as the host in a supported topology. However, NI-DAQmx guarantees that two tasks configured to start at the same host time always start at the same I/O Device Time in all scenarios, preserving precise synchronization between chassis in this common use case. Refer to Time Triggering in the NI-DAQmx User Manual for more information on accessing time-based features in the NI-DAQmx API.

    Timebases

    The following figure shows the FD-11601 clock routing circuitry and timebases.

    Figure 33. Clock Routing Circuitry


    You can use the 13.1072 MHz, 12.8 MHz, 12.288 MHz, and 10.24 MHz timebases to generate the AI Sample Clock signals. These timebases are generated directly from the onboard clock generator. By default, NI-DAQmx automatically chooses the most suitable timebase for a selected data rate. You can also manually select a timebase through the NI-DAQmx API.

    Refer to Timing Considerations for FieldDAQ and Master Timebase Synchronization in the NI-DAQmx User Manual for more information about configuring timing in the NI-DAQmx API.

    Synchronization Across a Network

    The onboard 100 MHz oscillator automatically synchronizes to other network-synchronized devices that are part of your local IEEE 802.1AS subnet.

    The 13.1072 MHz, 12.8 MHz, 12.288 MHz, and 10.24 MHz Timebases are derived from the oscillator, and are synchronized to it. Therefore, they are also synchronized to other network-synchronized timebases on your IEEE 802.1AS subnet. This enables measurement signals to be synchronized to other devices across a distributed network.

    The FieldDAQ devices use the IEEE 802.1AS protocol over the network to synchronize. They can be configured to use the IEEE 1588 "Delay Request-Response Default PTP" profile instead. These devices cannot synchronize with other 1588 profiles.