Data For True RMS

[Trevor Emil]

I have been using the Analog Discovery 2 for some data collection for reading a square wave, and it has worked perfectly. I found that the True RMS voltage in the logger gives me the best measurement. I want to recreate this same measurement with a microcontroller using a separate program, but I can’t figure out the exact formula WaveForms uses. From the documentation, I know that True RMS = Sqrt(sum(xi^2)/N) but I have no clue where to find where WaveForms gives me N. If I’m trying to read a 6.25 kHz square wave, and I have logger set to update every 100ms, where would I find N?

Thank you!

[JColvin]

Hi @Trevor Emil,

The N should just be the number of samples that are taken/displayed on the graph. WaveForms will automatically calculate the number of samples for you in the small gear tab next to the "Update" dropdown box. You can also delete the auto-populated value and type in the number of samples you want like I have done, which will automatically update the history dropdown.

Let me know if you have any other questions.

Thanks,
JColvin

[attila]

Hi @Trevor123

The N is the number of raw data samples, TrueRMS = Sqrt( Sum[1:N] (X ^ 2) / N )
It a simple RMS calculation: https://en.wikipedia.org/wiki/Root_mean_square

The Samples in the WF/Logger refers to the measurement steps in the chart. 

[attila]

Hi @Trevor Emil

8 hours ago, attila said:

Hi @Trevor123

The N is the number of raw data samples, TrueRMS = Sqrt( Sum[1:N] (X ^ 2) / N )
It a simple RMS calculation: https://en.wikipedia.org/wiki/Root_mean_square

The Samples in the WF/Logger refers to the measurement steps in the chart. 

 

[Trevor Emil]

On 3/9/2021 at 4:06 PM, JColvin said:

Hi @Trevor Emil,

The N should just be the number of samples that are taken/displayed on the graph. WaveForms will automatically calculate the number of samples for you in the small gear tab next to the "Update" dropdown box. You can also delete the auto-populated value and type in the number of samples you want like I have done, which will automatically update the history dropdown.

Let me know if you have any other questions.

Thanks,
JColvin

Okay, I have a follow up question:

Is there a way to change the sample rate? The "Samples" editor that you showed under the gear changes the number of samples shown in the graph (43 samples updated every 100 ms would only show an x axis of 4.3 seconds). Is there a way to see what the sampling frequency is for these readings? Is it only 10 Hz?