Single Read Analog Input timeouts with DAQmx 9.3/9.4

[nate_477]

Setup:
DAQ USB-6212
DAQmx 9.3 driver
VS2010 .Net 4.0
XP Pro SP3
KB969238 (USB DAQ XP Hotpatch)

My app does two single sample analog reads in a control loop every few seconds.  When app is run on my test PC the following exception occurs after several reads:  “Specified operation did not complete, because the specified timeout expired.  Status Code -200474”.  Using the same application and drivers on my development machine works fine, but the test PC fails quickly every time.

Just tried DAQmx 9.4 and updating Window drivers but no success.

[_enigma_]

nate_477,

This is Alexander M with National Instruments.  The issue you are experiencing is somewhat common with USB devices, but more importantly it is very common with single point measurements that are software timed.  Since Windows is non-deterministic, processor allocation will vary for each process.  In plain english, this means the actual execution time of any process is uncertain.

A single point measurement is not always the best way to collect data. Working back to our high school chemistry days, they always had us take multiple measurements and then average the results.  This concept should also be applied with Data Acquisition.  Using a Continuous Buffered Acquisition, we hardware time the acquisition while collecting multiple samples.  Below is a LabVIEW example of Continuous Buffered Acquisition.

Taking the mean of the multiple samples collected will give a better representation of a single point acquisition.

Alexander M

Applications Engineer

National Instruments