NI-DAQmx: Asynchronous Parallel DAQ Operations in LabVIEW

I. Description:
This example provides a method to run two parallel acquisitions on two different DAQ cards. It consists of two different DAQ tasks running in parallel WHILE loops.

This example program uses a subVI called "Asynchronous AI Read.vi." This reentrant subVI actually checks to see how many data points are available, and the program does not perform a read until the specified number of samples is available to read. The subVI accounts for timeout conditions using the LabVIEW Tick Count function.

The top level of this example employs LabVIEW notifiers to pass error or stop information between the two parallel loops. The notifiers are used to stop both loops if an error or stop request occurs in either. They are not an essential part of the asynchronous acquisition.

II. Instructions for Running:
Steps:
1. Create an analog input voltage channel.
2. Set the rate for the sample clock. Additionally, define the sample mode to be continuous.
3. Create a notifier for each board.
4. Call the Start VI to start the acquisition.
5. Read the waveform data in a loop until the user hits the stop button or an error occurs.
Note: This example reads data from one or more channels and returns an array of data. Use the Index Array function to access an individual channel of data.
6. Read the notifier status of the other board and also send a notification for the current board.
7. Call the Clear Task VI to clear the Task.
8. Use the popup dialog box to display an error if any.

IV. I/O Connections Overview:
Make sure your signal input terminal matches the Physical Channel I/O Control. For further connection information, refer to your hardware reference manual.

Requirements

Filename: cont_acq_async_read_daqmx.llb

Software Requirements

Application Software: LabVIEW Base Development System 7.1.1
Language(s): LabVIEW

Reader Comments | Submit a comment »

Asynchronous Read
The Asynchronous DAQmx Read function should be part of the base package! I can't imagine why you wouldn't want to use this, as it is far less CPU intensive than the standard DAQmx Read.
- Jan 31, 2006