Troubleshooting Offset, Incorrect, and Noisy Readings of NI Multifunction DAQ

Updated Oct 18, 2018

Reported In

Hardware

  • Multifunction I/O Device

Issue Details

  • How do I troubleshoot offset, incorrect, or noisy readings in my DAQ system?
  • My DAQ device is measuring incorrect values. How do I troubleshoot this issue?

Solution

First step in all systems:

  • Using a separate measurement device such as a DMM or oscilloscope, verify that the signal is behaving as expected at the input terminals of your DAQ device. This isolates the DAQ device as the error and ensures that the input signal is not being corrupted at some other point in your system.
 
  • Calibrate your device. Offsets, noisy and bad readings may also be caused by an analog to digital (A/D) converter that needs re-calibration. You may calibrate National Instruments data acquisition hardware manually. See Calibration for more information.

Troubleshooting offset readings:

  • Offset errors may be caused by incorrect settings for your DAQ hardware. If you have DAQ hardware with jumpers, then make sure that the jumper settings specified in software (i.e. in the Measurement & Automation Explorer (MAX) or the NI-DAQ Configuration Utility, depending on your NI-DAQ driver version) match the actual hardware jumper settings. This will affect how LabVIEW converts your measurements. For other programming environments, make sure that you specify the correct conversions for your measurements from NI-DAQ.

Troubleshooting incorrect and noisy readings:

  • Use shielded cables instead of ribbon cables in noisy environments, or when measuring mV signals in the absence of signal conditioning. You should also make sure that you are using the correct analog input mode for your signal (DIFF, RSE, or SE). Environmental noise may cause bad readings, especially if you have long wires (over 15 feet) between your transducers and your DAQ board (or SCXI module). See Field Wiring and Noise Considerations for Analog Signals for more information.
 
  • Sample at at least 10 times your signal's frequency, if possible. Many times, you may have to sample at even higher rates. Bad readings are often caused by aliasing, which is in turn caused by a sampling rate that is too slow. See Aliasing for more information.
 
  • If your device has user-programmable input ranges, be sure that the input range that is selected is that which minimizes noise and optimizes accuracy for your signal range. You can find this information in the specification sheet for your module.

Return your DAQ device for re-calibration and testing:

  • If you have exhausted all other troubleshooting tips and you still have offset or bad readings, then you may need to send the board to National Instruments for testing and re-calibration. National Instrument's data acquisition products are shipped with a document that guarantees operation within the stated specifications for a certain period of time (typically one year) known as the calibration interval. If you have owned your hardware for longer than its calibration interval, then you may have inaccurate readings, however, before you may return a board, you must first contact a National Instruments technical support engineer, so that we may help you with your troubleshooting efforts. See National Instruments Hardware Repair or Calibration for more information.

Additional Information

If you are using a C Series module, you can check the National Instruments Calculating Absolute Accuracy or System Accuracy to confirm that your data acquisition hardware is up to the task that you have set for it.

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