The cDAQ-9189 chassis features automatic network-based synchronization with compatible networks and IEEE 802.1AS-capable NI Linux Real-Time controllers. The SYNC logo on the chassis front panel indicate that the chassis are capable of hardware-based synchronization over a network.

The chassis supports IEEE 802.1AS synchronization, and all chassis timebases will be automatically synchronized. Refer to Networking and Synchronization across a Network for more information about supported topologies and other technical requirements.

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

Time triggers and timestamps 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 cDAQ-9189 uses internally. This time is determined by the network configuration and is shared by all 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 and timestamps 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 the Timing and Triggering topic in the NI-DAQmx User Manual for more information on accessing time-based features in the NI-DAQmx API.