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Setting the Default Polling Rate in the NI-DAQmx I/O Server

Primary Software: Driver Software>>NI-DAQmx
Primary Software Version: 8.3
Primary Software Fixed Version: N/A
Secondary Software: N/A
Hardware: Legacy DAQ Devices>>Multifunction DAQ

Problem: I want to change the default update rate for my NI-DAQmx I/O Server through an .ini file. But, I must subscribe to the server before I can update the rate. How can I set the default polling rate in the NI-DAQmx I/O Server?

Solution: The NI-DAQmx I/O Server uses a global virtual channel-like entity called the Server Polling Rate. The Server Polling Rate controls how fast NI-DAQmx reads from the input channels (AI, DI and CI) on DAQ hardware.



The default value of the Server Polling Rate is 1 Hz, with supported values in the range of 0.01 Hz – 1000 Hz. A NI-DAQmx I/O Server client application, such as LabVIEW, Server Explorer, or any OPC client software, can change the rate by subscribing to this channel and writing a new value to it. The change has a global affect. For instance, if multiple clients are connected to the NI-DAQmx I/O Server, they will all use the new value of the Server Polling Rate.

In NI-DAQmx 8.3 and higher, you can specify the default value for the Server Polling Rate through an .ini file by completing the following steps:

  1. Create a text file called daqmx.ini in the Program Files\National Instruments\Shared\Tagger folder.
    Note: This folder should already contain other files with a .mnd extension, such as daqmx.mnd.
  2. Specify the new default rate using the following .ini file entry:
    DefaultServerPollingRate = X
    Note: X is your sample rate.
  3. Restart your computer.

The NI-DAQmx I/O server now reads the .ini file setting when it loads. If a valid rate is specified, it uses that rate as the default value of the Server Polling Rate. If the daqmx.ini file does not exist, or if the value specified in the .ini file is invalid, the NI-DAQmx I/O Server continues to use 1 Hz as the default rate.

Related Links:

Attachments:


ServerPollingRate.JPG - ServerPollingRate.JPG

Report Date: 08/02/2006
Last Updated: 03/05/2007
Document ID: 401J4Q17

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