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Measure the Dynamic Range of My Data Acquisition Device with NI Software

Updated Mar 10, 2022

Environment

Software

  • LabVIEW Full
  • LabVIEW NXG
  • DAQExpress

The dynamic range of a DAQ device is the ratio of the highest signal level to the smallest signal level a circuit can measure (usually equal to the noise floor), normally expressed in dB.

One approximation of the Dynamic Range is the dB equivalent of Idle Channel Noise which you can find using the following method in LabVIEW. The industry standard (and SVMS Dynamic Range SubVI) technically requires a high quality -60dB input tone instead of a terminated input channel. For most NI devices you get the same number using either method.

The same method should be valid in different Application Development Environments (ADE) such as LabWindows/CVI™ or DAQExpress. Refer to your ADE documentation to locate functions or methods equivalent to those used in the shown LabVIEW snippet. 
 

  1. ​Terminate an input channel.
  2. Calculate the offset and subtract it from the original signal.
  3. Convert the remaining signal to Vrms (Idle Channel Noise).
  4. Convert input range to Vrms (Full-Scale Amplitude of AI Channel).
  5. Divide the two values and convert them to dB.

Below is a LabVIEW code snippet showing how to perform the calculation using the Mean VI, RMS VI, and Logarithm Base 10 Functions.


Note: This image is a LabVIEW snippet, which includes LabVIEW code that you can reuse in your project. To use a snippet, right-click the image, save it to your computer, and drag the file onto your LabVIEW diagram.

Likewise, in LabVIEW NXG and DAQExpress, you can use the Statistics, Amplitude Measurements (in AC DC and RMS mode), and Logarithm Base 10 nodes to perform the calculation.