Synchronizing Multiple tasks (reference triggered)

[AntonioERamirez]

Hardware:

Chassis: NI PXIe-1078

Multi-Function DAQs: 5 NI PXIe-6368

Timing Module: NI PXIe-6683H

Goal:

Use a reference trigger to acquire data from multiple tasks with each task containing channels from only one card (for multiple sampling rates).

Program:

the attached vi makes 2 tasks with the first task containing 1 channel from 1 DAQ and the 2nd task containing 1 channel from another DAQ (for simplicity). In order to use a reference digital trigger, the sampling mode has to be set to Finite Sampling. when I acquire the triggered data, the data is not synchronized, as shown in the picture, even though the Reference clocks are set to PXIe_clk100 backplane clock. however, when I use continuous sampling mode and start digital trigger, the data is synchronized.

how do I ensure synchronization when using reference digital trigger?

[JÞB]

Well, First.  DO NOT modify shipping examples without saving them with a new name to a new location.  Doing that is a lot like unloading a handgun by pointing it at your own foot and pulling the trigger.

So, you modified the example and changed the value of the DAQmx Trigger Sync Type property of both tasks to "None" and noticed "trigger skew" in the data.

When sharing a trigger across multiple devices, the master device must respond to and export the trigger, and the trigger signal must travel from the master device to slave devices. This results in skew in the trigger signal. On some devices using Reference Clock synchronization, you can compensate for that skew by locking the trigger to the Reference Clock or to a clock derived from the Reference Clock. When you lock triggers to a clock, the device responds to those triggers on a subsequent edge of that clock, rather than immediately. Therefore, skew correction results in increased latency.

To enable trigger skew correction for an application, specify which device is the master and which devices are slaves using the SyncType DAQmx Trigger property.

[AntonioERamirez]

I did save it to a different location, with a different name (TriggerTest2.vi), and before any modifications. Shipped example is still intact. I don't know why it still says the original name and then in brackets says the actual file name.

 I should have mentioned on my first post but:

I have tried setting sync type to master/slave with digital start trigger and I still get skew data. However, when I set the sync type to none and use digital start trigger the data is synchronize.

When I use the reference trigger, which requires finite sampling, the data is skewed regardless of sync type, master/slave or none.

I'm not sure what's going on here.

[JÞB]

What are the devices?

Have you queried Sync Pulse.Reset Time for each device?  Did you then set the Sync Pulse Reset Delay properties?

[AntonioERamirez]

the devices I am using are 5 NI PXIe-6368 multifunction DAQs

which vi or property node is used to do that?

[JÞB]

 Mobile now... It is still available from the timing pnode.  More sub section.  The detailed help ... Helps

[AntonioERamirez]

I don't see those properties in DAQmx Timing Property node. I have labview 2016.

[JÞB]

Let me point you here

I don't have hardware to play with but most of what we've discussed so far is explained in detail there