How to Choose my Sampling Frequency to Get a Proper Signal Shape?

Updated Mar 3, 2018

Reported In

Hardware

  • NI-9242
  • NI-9219

Issue Details

  • I am reading the correct frequency, however my amplitude is incorrect.  Sometimes it is too small, sometimes it is nearly correct.  How do I make the amplitude consistently correct?  I am sampling at the Nyquist Rate.
  • I am working on a data acquisition system. The voltage and current signals are sinusoidal, however when plotting them using the below sampling frequency, I am receiving a different shape:
I/O Sampling Frequency= 2.5 * Frequency_Signal
 
What is the best sampling frequency  that will reproduce a correct shape of my signal?

Solution

According to the Shannon Sampling Theorem, you can maintain the frequency content of the signal by sampling at the Nyquist rate; i.e. using a sampling frequency at least twice the maximum frequency component in the sampled signal. Maintaining the frequency content does not mean maintaining the signal shape.
 
If you want to receive a proper signal shape, as a rule of thumb, you should sample at 10 times the signal frequency; i.e. if the sinusoidal is at 50Hz, you should sample at 500Hz, which means a sampling period of 2ms.
This link demonstrates different cases on sampling, showing clearly the difference in shape when sampling at 10 times the frequency of the input signal.
 

WAS THIS ARTICLE HELPFUL?

Not Helpful