Simultaneously Start Multiple Modules Using a cDAQ Chassis in SignalExpress

Issue Details

I'm using SignalExpress with a multi-slot cDAQ chassis and would like to start multiple modules simultaneously. Is this possible, and if so how can I configure it?

Solution

In SignalExpress and depending on your hardware, you have three methods to start the modules at the same type:

1. External trigger
2. Channel Expansion or Multidevice Task
3. Timestamp based Start Trigger

1. External Trigger

To use this method, you must have a CompactDAQ chassis with one or more built-in PFI lines or a parallel digital I/O module. Refer to Digital I/O Considerations for C Series Devices and cDAQ Module Support for Accessing On-board Counters to learn what modules can be used to import external triggers.

You can then take the PFI lines on the digital module to import an external trigger. On your DAQmx step, select the Triggering tab and select Digital Edge for the Trigger Type field. Choose the PFI lines your trigger signal is wired to in the Trigger Source field.
 
At this point, you should be able to use a digital signal from your digital module to trigger the tasks simultaneously.

2. Channel Expansion or Multidevice Task

Channel expansion is the easiest method to synchronize and start multiple modules. However, it is limited to modules of the same time (e.g. all modules must be Analog Input) and all the modules will need to acquire or generate at the same sample rate. If you need to synchronize modules of different types or the modules need to acquire or generate data at different rates, refer to the other methods in this document.

If the aforementioned limitations are not a problem, when you add the step to the SignalExpress project, expand the modules you want to synchronize, press the Ctrl key and click on the channels you want to add to the step.
If the step already exists, click the Add New Channels button to add the channels of the other modules.
    
For more information about Channel Expansion or Multidevice Tasks, refer to Easily Synchronize and Trigger NI-DAQmx with Channel Expansion, Channel Expansion Explained, and C Series Multidevice Tasks .

3. Timestamp Based Start Trigger

This method can only be used if you have a Time Aware chassis (cDAQ-9185 or cDAQ-9189). With a time aware chassis, you can use a timestamp to specify when the modules should start acquiring using a timestamp. However, this method requires readjusting the timestamps every time the project needs to be executed, so it may not be practical if you need to execute it several successive times.

To use this method, select the start time in each step you want to start simultaneously by going to the Triggering tab, selecting Time as the Trigger Type and selecting a Start Time.

Refer to How to Achieve High-Accuracy Measurements With NI-DAQmx-Based TSN Devices for more information about Time Aware devices using Time Sensitive Networking (TSN).

Additional Information

• The synchronization methods discussed in this document are not valid for Counter Input tasks. Counter Input task triggering can only be performed through internal lines that are not available in SignalExpress and therefore requires the use of an Application Development Environment (ADE) like LabVIEW or LabWindows/CVI.
• To learn how many tasks of each type can run at the same type on your CompactDAQ Chassis, refer to How Many Different Tasks Can Concurrently Run on a CompactDAQ Chassis Gen II?  and Timing Considerations for C Series Devices .
• For more comprehensive information about C Series Synchronization in CompactDAQ, refer to Synchronizing Analog Input C Series Modules with NI-DAQmx in LabVIEW.
• When using an external trigger method, you can generate a pulse with a Counter Output step on the selected PFI line to start all tasks expecting the trigger. That way you won't need to provide a trigger signal externally.
• When using channel expansion or multidevice tasks, if the tasks includes channels from a mixture of C Series Delta-Sigma devices, you must account for filter delay differences between the devices. Refer to Why Is My Data Delayed When Using DSA Devices? for additional information.