Table Of Contents

Synchronization

Last Modified: June 28, 2021

Synchronize your system to coordinate inputs within a module or device, between modules in a single chassis, or between multiple devices or chassis.

When you synchronize devices, FlexLogger correlates their inputs in time. If you do not synchronize devices, their inputs may have a large initial skew and drift over time. Skew refers to the difference between input start times (t0) relative to other channels. Drift refers to the change in skew over time.

Unless noted otherwise, inputs in FlexLogger are generally hardware-timed and support synchronization. For hardware-timed inputs, a digital signal such as a clock on your device controls the rate of generation.

Refer to the following topics to learn more about synchronization in FlexLogger:

Why is my data not synchronized?

Not all devices support synchronization and not all devices that support synchronization can be synchronized in FlexLogger. Inputs from some devices may have skewed start times and drift over time relative to other channels. For software-timed inputs, the rate at which the signals are generated is determined by the software and operating system. Since software-timed inputs are not timestamped using a hardware clock, they cannot be synchronized. To learn more about synchronization, visit Synchronization Basics on ni.com.

The following table describes some example scenarios where inputs may not be synchronized. For help with troubleshooting synchronization issues in your system, contact NI Support.

Scenario Notes
You are using multiple chassis. Refer to Synchronization Status for more information.
You are using simulated inputs. FlexLogger does not synchronize simulated inputs.
You are using a PXI or PXIe Digital I/O module. The hardware-timed PXI or PXIe Digital I/O modules use their own sample clock that is not rate-locked. Inputs from PXI or PXIe Digital I/O modules cannot be synchronized with the inputs from other modules in the chassis.

The inputs on the other modules in the chassis will be synchronized to one another.

You are using an NI-XNET and DAQ module within a PXI chassis or a Time Sensitive Networking (TSN)-Enabled Ethernet cDAQ chassis. FlexLogger does not currently support synchronization between these types of modules. There will be a nondeterministic skew between inputs from these two types of modules but the inputs will not drift.
You are using an NI-XNET module and a C Series Delta Sigma (DSA) module in the same USB or non-TSN enabled Ethernet cDAQ chassis. FlexLogger does not currently support synchronization between these types of modules. When you configure a DSA module, it generates the sample clock timebase that all DAQ modules in the chassis use, and the DSA module cannot share that clock with any NI-XNET modules.

Refer to the hardware documentation for your module if you are unsure whether you have a DSA C Series module.


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