Waveform averaging

[LVU14]

Hello.

I have to acquire noisy sine signal (about 30 kHz) with NI PXI-5105 60 MS/s digitizer. I tried to make a VI using LabVIEW help but got the following result:

Apparently, it is necessary to make waveform averaging but I don't know how to do such a thing.

Here shows how signal is indicated:

I found here the following example from RavensFan, but could not use it:

There is a type mismatch:

Is there somewhere a detailed description of the LabVIEW's waveform / complex waveform / … data types with examples? I so stupid and standard LabVIEW help did not help me.

Thanks in advance for your help and sorry for my poor english.

[GerdW]

Hi LVU,

a waveform apparently is more than a simple 1D array…

Can you switch your NIScopeRead from "1D DBL" to "Waveform"? Then you could adapt RavensFan's example easily!

LabVIEW comes with a function palette dedicated to waveforms (like this). Those functions also have their example VIs…

[Henrik_Volkers]

Could you tell us what characteristic of your waveform you want to measure?

[LVU14]

I changed the setting on the "1D WDT", but got the same "jumping" waveform that is shown above without averaging. Seems like the divisor is always "1" and the summation in "for loop" doesn't work. I have to remake the loop but so far I didn't get. Here I need a deep knowledge of debugging in LabVIEW.

[Henrik_Volkers]

just trigger at zero and adding up values migth not help you much ... unless you want the DC value 😄

... again: What do you need (or expect 😉 ) to measure (or see)?

[LVU14]

I have to measure the RMS voltage and frequency of the signal.

[Henrik_Volkers]

Try:

Extract Single Tone Information VI

Owning Palette: Waveform Measurements VIs

Requires: Full Development System

Takes a signal in, finds the single tone with the highest amplitude or searches a specified frequency range, and returns the single tone frequency, amplitude, and phase. The input signal can be real or complex and single-channel or multichannel. Wire data to the time signal in input to determine the polymorphic instance to use or manually select the instance.

and

Averaged DC-RMS VI

Owning Palette: Waveform Measurements VIs

Requires: Full Development System

Calculates the DC and RMS values of an input waveform or array of waveforms. This VI is similar to the Basic Averaged DC-RMS VI, but this VI gives more precise control over the individual DC and RMS calculations.

Do you really want the RMS or the amplitude of the 30kHz signal??

Have a look at the (power) spectrum of your signal ..  will help you identify (and eliminate)  the noise.

[LVU14]

Thanks. I will try to take your advice in the near future.

Additional problematic task is to show the signal on the front panel as it is, with the noise, but not bouncing/"jumping" waveform. It seems that the NI PXI-5105 scope does not have enough sampling rate. Using an external scope I got quite satisfactory signal representation for my task:

Analog scope gives a smoother waveform, of course.

I found the persistent mode with adjustable hold time in the "Scope Soft Front Panel" application, but it seems that to implement such a thing in VI is very difficult.

[Henrik_Volkers]

trigger at 50% 🙂

or in addition  use the intensity graph and add the traces (decimated to pixel width) with an overall exponential decay

here is an old forum example from altenbach found here , with a minor change 😉

[LVU14]

Hello.

What does "trigger at 50%"?

Thanks for intensity graph example. It's awesome! Quite a complicated VI. To adapt it to my task will take several years )

Extract Single Tone Information VI gives values ​​bouncing (The same results that are obtained using niScope Read Measurement VI and Statistics Express VI)

Averaged DC-RMS VI gives an empty array/graph. I will try to change the parameters to get the results.