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Binding NI-DAQmx Strain Task Data to Shared Variables

Updated Nov 12, 2018

Reported In

Software

  • LabVIEW

Driver

  • NI-DAQmx

Issue Details

I am following the Using the LabVIEW Network-Published Shared Variable and OPC With NI-DAQmx with the goal of reading my DAQmx strain data on an OPC client. The tutorial proposes two possible solutions, including binding to both local (project) and global (NI MAX) NI-DAQmx Virtual Channels with shared variables. However, when following the tutorial I found that I was unable to set certain attributes of my acquisition such as timing and sample clock source due to those properties being DAQmx task properties and not channel properties. How can I get my DAQmx task data to my OPC client? 

Solution

Because DAQmx timing configuration settings such as sample rate and sample clock are DAQmx task properties and not channel properties, a more traditional method has to be used to publish your acquired data to a shared variable. In LabVIEW, you can use a DAQmx example program that acquires analog strain data as a starting point and from there simply write your data received by the DAQmx Read VI to a network published shared variable. Once a Shared Variable has been created using the Network-Published scope, all data written to the variable is available to all systems networked with the host computer, including a OPC quick client. 

For more information, refer to section 3 of Using the LabVIEW Shared Variable.
 

Additional Information

NI-DAQmx uses NI-PSP to interact with the Shared Variable Engine and make data read by the driver available to all networked devices. NI-DAQmx automatically produces PSP objects for all NI-DAQmx global virtual channels configured in MAX and all NI-DAQmx local channels created in LabVIEW, though it does not publish data from NI-DAQmx tasks.

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