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Part of the M Series Synchronization with LabVIEW and NI-DAQmx Example Set
Other data acquisition devices, such as E Series, do not offer a reference clock for synchronization purposes. A common way to synchronize these devices, which will also work for M Series devices, is to share a common sample clock across all devices in the acquisition. This can be done by routing the master sample clock over RTSI to be used as the sample clock for all slave devices. There are slight disadvantages with using this method. One is that small propagation delays are introduced between the master and slave by routing the sample clock over RTSI that do not exist when using a reference clock for synchronization. The second is that although a common AI Sample Clock is shared between all boards, the AI Convert Clocks that actually cause the A/D conversions on each channel for devices with multiplexed architectures (such as E Series and M Series) are still generated from each onboard oscillator, which will not be synchronized to each other. However, these errors are small and negligible for most E and M Series applications.
The example shown in Figure 1 demonstrates how to synchronize an acquisition between two M series devices by sharing a sample clock. With NI-DAQmx, the master sample clock will automatically be routed to the slave over RTSI bus or the PXI trigger lines by setting the source of the slave sample clock to be the master sample clock. Below are the descriptions of each of the steps labeled by the numbers on the figure.
Figure 1 Synchronization of Two M Series Devices Using the Sample Clock
Example code from the Example Code Exchange in the NI Community is licensed with the MIT license.