The cDAQ-9185, cDAQ-9189, cRIO-904x and cRIO-905x models offer three distinct clocks (10 MHz, 12.8 MHz, and 13.1 MHz) to Delta Sigma and Reference Clocked Modules. When using Delta Sigma or Reference Clocked Modules in these chassis DAQmx will default to using the chassis clocks to acquire or generate signals instead of the clocks onboard the modules.
When the time-aware chassis share the same grand master, all clocks onboard the chassis are synchronized to this grand master. Thus, clocks across multiple chassis are synchronized to each other. This process is done automatically and without user input. Since each module in the chassis will default to using the chassis backplane clocks for generation or acquisition, clocks used by each module (master timebase, sample clock, and/or reference clock) will all be synchronized. To synchronize the module acquisitions or generations between chassis, ensure that the Start Trigger is sent at the same moment.
Having multiple devices in the same task will compensate for timing difference between modules automatically, which greatly simplifies task setup and makes this configuration ideal for small to moderately sized acquisitions. There are a few caveats:
- Having a large number of channels in the same task will cause task set up to take longer as all channels are configured to start at the same time. This extra set up time must be accounted for when setting a time start trigger or error -209840 may occur.
- Having multiple chassis in the same task will make the task less reliable, as losing contact with any chassis in the task will stop the task. For a more robust configuration, use one task for each chassis.
Figure 1: Multichassis Synchronization with the cDAQ-9185 or cDAQ-9189