Error -209838 Sync Lock Lost When Running a Real-Time Executable With IC

Updated Aug 1, 2018

Reported In


  • Industrial Controller
  • CompactRIO Controller
  • cDAQ-9189
  • cDAQ-9185


  • NI-DAQmx 17.6
  • NI-DAQmx 18.0

Issue Details

I have a TSN-enabled device connected to my real-time industrial controller. When I try and run my real-time application, sometimes I get the following error:

 DAQmx Error -209838  Synchronization lock was lost during operation. If the occasional loss of synchronization is acceptable, change the Synchronization Unlock Behavior property to ignore sync loss. Otherwise, go to for more information about sync loss management.

If my TSN device is on before my industrial controller, this error happens every time


Update to DAQmx 18.0 or later. If this is not an option, use one of the workarounds listed below:
  • Make sure that your real-time controller starts before your TSN device.
  • If that's not possible, restart the DAQmx task once the controller starts to accomplish the same effect.

Additional Information

This error was fixed in DAQmx 18.0. It error occurs because the IC is still in the process of booting up and potentially starving the PTP process. It then exceeds the expected timeout and claims a sync loss.