Jagged wavy singal by 9237 at no load condition

[Henrik_Volkers]

your data show a clear 50 Hz line 😕

so sample with 1kSPS and filter or mean over one periode (20ms) the data

the example below show the filter artifact  (tune in)  for the first xx points ...

You wrote you want to see a 2Hz periode. If you want to measure the relation between two signals I strongly recomment to use the tone detection vi (with a narrow search field) on the noisy signal(s) ..(capture more than 10 periodes (or 5 but match the window length to 5 periodes) )

[ksrkm]

Thank you Henrik for your reply.  I am unable to open your file read lvm filter fft.vi ( in the format of version 12) using my LabView version of 9. Could you please send me this file in Version 9.

Sincerely

KSRKM

[Henrik_Volkers · Accepted solution]

Here it is...

I added a mean value calculation  and mean over n periodes

Your 100Hz data is actually sampled with 1612,9Hz  🙂

So my recommendation is to sample with 2000Hz, capture a multiple 40 values  ( = 20ms = one 50Hz power line periode) and calculate the mean

You can use the decimate vis to do that. 

[ksrkm]

Thank you so much for your suggestions and providing me the vi file. Right now I am studying your vi file and trying to understand it. I do not have much idea in LabView programming. I get back to you soon after I do one or two experiments with the vi file provided by you. I once again thanks for your sincere efforts to attempt to resolve my problem.

Sincerely

KSRKM

[ksrkm]

Dear Henrik

 I have studied your *.vi file and I have a few doubts on your vi file. Please clarify me

1. Why does the "Read from measurment file" command reads only first 500 samples. How to instruct this command to read also next 500 samples or indeed to read the entire data in the file.

2.  You have ageraged the data of first 480 samples (using an approach) and also averaged all 500 samples (straight way).Will there be any difference in these two types of averaging approaches in general? If so, then which is the correct way of averaging.

3. I did not understand why for loop is provided around averaging process. I think is executed only once. Please correct me if I am wrong.

4. Please provide me the steps to extend the present procedure given by you to all the data  in a typical lvm file i.e., not limited only to 500 samples.

Sincerely

KSRKM

[Henrik_Volkers]

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@ksrkm wrote:

Dear Henrik

 I have studied your *.vi file and I have a few doubts on your vi file. Please clarify me

1. Why does the "Read from measurment file" command reads only first 500 samples. How to instruct this command to read also next 500 samples or indeed to read the entire data in the file.

you provided max 500 samples ... have you tried it with a file of more samples?    (Well double click on the read vi an check..... and reading the help file helps 😉 )

2.  You have ageraged the data of first 480 samples (using an approach) and also averaged all 500 samples (straight way).Will there be any difference in these two types of averaging approaches in general? If so, then which is the correct way of averaging.

read my former post.....   if you don't mean complete periodes of the line noise you will get more errors but if you mean a looong time this error get smaller and vanish in the residual noise.... just think (and learn) about it.

3. I did not understand why for loop is provided around averaging process. I think is executed only once. Please correct me if I am wrong.

it's using auto indexing of the array of wfrms , so it executed 3 times, once for every channel you saved in the lvm

4. Please provide me the steps to extend the present procedure given by you to all the data  in a typical lvm file i.e., not limited only to 500 samples.

read the help file of the reading vi... 😉    I'm not really used to express vis.... but the help file told me that you can have to the vi in a loop (reading a segment of same size as you saved it)  until the EOF is reached

Sincerely

KSRKM

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[ksrkm]

Dear Henrik

Thank you for your all replies. Yes I need to study LabView part to get the better results. I will conduct some real time experiments and I will get back to you on the results with incorporation of your suggestions.

Sincerely

KSRKM

[ksrkm]

Dear Henrik,

1. Please find two files attached on my doubts. Please also note that I have used the same data file used by you to demonstrate the effect of filtering and averaging.

2. I have added a waveform graph to the output of spectral measurments of filtered signals in your given *.vi, in addition to the mixed-signal graph. Interestingly, this graph shows, in contrast to your results in mixed-signal graph, components containing frequencies beyond 60Hz. My waveform graph shows as if there is no filtering is done!!!!!!!. In fact, I see wave forms upto 1000 Hz are present even in the filtered signal!!!. But your mixed-signal graph shows there are no more components after 60Hz. I do not understand why there is two types of displays for the same signals after FFT.

3. You have provided an input in the front panel named: "Lower-Cut-Off" (given a value 30) to the filter. However, if you double click filter, you also find cut-off frequency (given a value 25). In your *.vi which value of cut-off frequency (30 or 25) will be considered by the program?

Sincerely

KSRKM

[Henrik_Volkers]

In short , take some lessons in signal processing ..... (nowadays you get good lectures at youtube)

and on my fft graphs I simply scaled up to ?? Hz....if you choose db and autoscaling you will always see a signal 😄

What does -220dB mean??

[ksrkm]

Dear Henrik

Thank you for your tips. Yes I have now understood your program. You have scaled both x and y axis. Unfortunately I was not observing the amplitude of the signal and the signals more than -160 dB (your cut-off) have low amplitudes. I am very happy now that I can now aquire signals with better understanding. Now I am able to program in version 9 the way you have doen in version 14. Thank you so much for providing me a very useful *.vi file and your tips on labview programming.

Sincerely

KSRKM