Setting the Polling Rate of a NI-DAQmx Channel Shared Variable

Updated Mar 1, 2019

Reported In

Software

  • LabVIEW
  • LabVIEW Datalogging and Supervisory Control Module

Issue Details

I am using the LabVIEW Shared Variable Engine to publish data from an NI-DAQmx channel, but I want the data to update faster. How do I set the rate at which the shared variable polls this channel?

Solution

There is a network-published shared variable available on the host computer called Server Polling Rate that allows you to set how often an NI-DAQmx channel is polled for data. Valid rates for this variable are 0.001 - 1000 Hz. 

To access this polling rate in LabVIEW, you must create a new shared variable within your project and alias it to the Server Polling Rate variable.
To do this, follow these steps:
  1. In the LabVIEW project window, right-click on My Computer and select New»Variable.
  2. Make sure Variable Type is Network-Published and choose a name for your variable.
  3. Select the checkbox, Enable Aliasing.
  4. Choose PSP URL from the Bind To drop-down listbox.
  5. Click Browse to select the path to the Server Polling Rate variable.
  6. Expand <YourComputerName>»System»DAQmx, select Server Polling Rate, and press OK.
  7. Select write only or read/write as the Access Type.
  8. Press OK.
Once you have created this shared variable, you can write to it in your application to set the polling rate. 

If you are using the Distributed System Manager, you can set the value of the Server Polling Rate variable by performing the following steps:
  1. Expand My Systems»localhost»System»DAQmx and select Server Polling Rate.
  2. In the New Value field, enter the desired polling rate in Hz.
  3. Press Set.
If you are using a different OPC client, steps will vary. However, the Server Polling Rate will be accessible as an OPC tag located at System/DAQmx/ under the Prog ID National Instruments.Variable Engine.1.
 

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