Offset on First Sample When Acquiring on USB-628x Module

Updated May 3, 2018

Reported In

Hardware

  • USB-6289
  • USB-6281

Driver

  • NI-DAQmx 9.6.1

Issue Details

When performing analog acquisition with my USB-628x device, my first sample appears to be offset by some amount and occasionally falls outside the accuracy specification of the device.

For example, when performing a finite acquisition of a known 0 V source at 10kS/s and reading 100 samples, I get the following result: 



Note that the first sample is offset from the subsequent samples by a non-trivial amount.

Solution

This is a known issue with USB-628x modules, and is fixed in DAQmx 9.6.1.

This issue only affects USB-628x devices and causes the samples to be inaccurate if the time between conversions exceeds 2 ms. This affects the first sample of any data acquisition; however, if the sampling rate is less than 500 S/s (greater than 2 ms between conversions), then it is possible for all samples to be inaccurate.

Correcting this issue requires one of the three options below:
  1. Upgrade all computers used to control the USB-628x module to DAQmx 9.6.1. (note: This will only resolve the issue for the computers that are updated to DAQmx 9.6.1. If the module is connected to a computer with a DAQmx version less than 9.6.1, the issue will still exist)
  2. Download and run the NI USB-628x Update Utility (attached at the bottom of this article). This will reconfigure the device's internal settings and allow the issue to be fixed regardless of the DAQmx version being used. Detailed instructions on how to install and run the utility is listed in the "Additional Information" section.
  3. Send The device to our RMA department and National Instruments will reconfigure the device's internal settings for you. To setup an RMA, call 1-877-493-2406

Additional Information

To install and run the USB-628x Update Utility, follow these instructions:
  1. Download and run the attached file titled USB-628x Update Utility.exe.
  2. Click Yes on the prompt asking "Do you want to allow the following program to make changes to this computer?"
  3. Click Unzip on the self-extractor window:
  4. Press Next through the installation prompts to complete the installation.
  5. Make sure your USB-628x device is plugged into your computer at this point.
  6. When the utility has finished installing, go to Start»All Programs»National Instruments»USB-628x Update Utility, and run the utility.
  7. Select your USB-628x device from the drop down menu and press Update.
  8. This utility will now update your device's internal settings to correct the issue.

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