Synchronizing Multiple NI CompactDAQ Chassis

 The National Instruments Getting Started with NI-DAQmx Series is aimed at helping you learn NI-DAQmx programming fundamentals. Through video and text tutorials, this series will take you from verifying your device's operation in Measurement & Automation Explorer (MAX) to programming data acquisition applications using LabVIEW. It is intended for both the beginner who wants to learn how to use the DAQ Assistant, as well as the experienced user who wishes to take advantage of advanced NI-DAQmx functionality.

Overview

Many applications require precise control of timing and the ability to synchronize multiple operations. National Instruments Compact DAQ data acquisition devices provide excellent tools for synchronization and are well suited for these applications.

This paper will present and analyze the recommended methods for multi-chassi Compact DAQ synchronization for high-resolution DSA modules as well as non-DSA modules with NI-DAQmx measurement services, and NI LabVIEW. NI LabVIEW is the graphical development environment for creating flexible and scalable test, measurement, and control applications rapidly and at minimal cost. With LabVIEW, engineers and scientists interface with real-world signals, analyze data for meaningful information, and share results and applications.

Hardware Required

2 - Compact DAQ chassis

2 - 9401 Modules in Slot 5 or 6, to gain access to the chassis PFI lines

2 - Analog Input C-Series Modules

2 - 25-pin D-Sub cable with gender changer to connect the 9401 modules together.

Synchronization

To synchronize multiple CompactDAQ chassis, you will need to export and import timing and triggering signals through the chassis PFI lines.  In order to gain access to these PFI lines, you must have a DIO module in either slot 5 or 6 of the cDAQ chassis.  The NI 9401 module is recommended for this because it can serve as both an input and output module.  Please take note that the NI 9401 is an isolated DIO module.  You must connect the COM pin of the 9401 modules when synchronizing chassis to ensure proper signal integrity. Connecting the 25-pin D-sub cable (with the gender changer on one end) between the 9401's will connect all of the PFI lines as well as the COM pins.

Using modules like the 9211 or 9215

You will need to export the timing and triggering signals from the master chassis to the slave.  This will be done with Export Signal Property Node. This property node will be setup as seen in Figure 1.  The signals needed are the Sample Clock, and the Start Trigger.  While the master chassis is configured to export these timing signals, the slave chassis will be configured to import these signals as seen in Figure 2.

Figure 1

Figure 2

See the sync_9211_9215.vi below for an example using these property nodes.

Using modules like the 9233 or 9237

These modules we will need to export a slightly different set of signals.  These signals include the Sample Clock Timebase, the Sync Pulse, and the Start Trigger.  You can set up the Export Signals Property Node as see in Figure 3. 

Figure 3

These modules will also require you to use a Timing Property Node on the master and slave chassis to import these signals as seen in Figure 4.  Note that the slave chassis' Timebase is set to the same value as the master chassis through the use of a second Timing Property Node.  This will enable us to import these signals into the slave task.

Figure 4.

Once those signals are setup for the master and slave devices you can setup the rest of your DAQmx task and read your channels as expected.

See the sync_9237_9233.vi below for an example using these property nodes.

You have finished synchronizing your Compact DAQ chassis.  You will now only need to connect all the physical signals you wish to acquire data from and test your application.  Any physical channels you connect signals to will need to be specified.

Downloads

sync_9237_9233.vi

sync_9211_9215.vi

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