Getting False Result with Tone Measurement Express VI

Updated Jul 25, 2019

Reported In

Software

  • LabVIEW
  • SignalExpress

Issue Details

When I measure a sinewave with Tone Measurement Express VI, I get an apparently wrong result (amplitude, frequency, phase). My input signal is a 1Hz sinewave, with Vpp 1V. With the Sampling Rate 10k and Number of Samples 1k, the measured frequency of Tone Measurement Express VI is 14~16Hz, and the measured amplitude is 0.02. What is the matter?

Solution

The reason is that the Tone Measurement Express VI measures a sine wave signal correctly only when the samples used for measurements consist of at least one full cycle.
To resolve that, you can either:
  • Increase the signal frequency to be larger than Frequecy Resolution (Sampling Rate/Number of Samples).
  • Increase the Number of Samples to include at least a full cycle.
  • Lower the Sampling Rate.

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