First three harmonic analysis

[pbsalunkhe]

Hi Mark
Thanks for you reply.

I changed the "dt" parameter in "Build waveform" function to 0.1 instead of 0.0001 for 10 kHz sampling frequency and 1000 number of samples. Now it is showing correct time with the earlier vi. So I didn't need to change the vi as you suggested in last post.

However, when I am using DAQ Assistant for pressure data acquisition, I am putting dt=0.0001 corresponding to 10 kHz sampling frequency and it is showing the correct real time.
This difference, is it because in former case, I am using the "Build waveform" function outside the while loop and "dt" corresponds to measurement interval between two samples rather than interval between two points?

Thanks you

Pramod

[Sappster]

Yes you are correct, it is because the dt in this case is between sampled buffer reads and not the actual points themselves.

[pbsalunkhe]

Hi Mark

Earlier I carried out few experiments with dt=0.0001 instead of dt=0.1. Can I use the same data by multiplying the x-scale by 1000?

Thanks

Pramod

[Sappster]

Hi Pramod,

You are basically multiplying the x scale by 1000 by changing the dt like that. I'm not sure if I understand your question.

Does the data appear different after you change that?

[pbsalunkhe]

Hi Mark
Sorry for late reply.
You are correct. I am basically multiplying the the x-scale by 1000 to change the dt parameter. It is not affecting the waveform shape.
While acquiring the specific harmonics, the y-axis is amplitude (by default). I guess its unit is PSI (which I converted from Volt to PSI after DAQ Assistant).
I searched in LabView help to get the details on how the LabView acquires or calculates the first three harmonics, however I didn't got this information.
Can you please let me know if you know any LabView link which gives these details?

Thanks

Pramod

[Sappster]

Hi Pramod,

Here is some information about Harmonic Distortion calculations. Let me know if this doesn't answer your question.

http://zone.ni.com/devzone/cda/tut/p/id/3401

[pbsalunkhe]

Hi Mark

I saw the link and also searched in the developer zone to get other information. It worked for me.
I need to measure the max. frequency content in my signal. When I use DAQ Assistant, I have to enter the sampling frequency. In the output graph/chart, it shows Nyquist i.e half the sampling frequency. But how can I check the max. frequency in my signal?

Thanks

Pramod

[Sappster]

Hi Pramod,

By definition Nyquist frequency is the highest frequency you can detect. You will have to increase your sampling frequency to detect higher frequencies. Here is some information about singal acquisition and processing:

http://zone.ni.com/devzone/cda/tut/p/id/3216

Let me know if there is anything else I can help with.