Compare two sound signals in motors when varying load conditions

[Nipuna]

Hello Everyone,

I am very new to LabVIEW and DSP. I am trying to analyse the acoustic signature of a motor to identify the defects. But still, I am struggling with LabVIEW. I appreciate a few clarifications for the following,

1. To take the difference in amplitude and plot a graph time vs change of amplitude 

2. How to derive an equation from the plotted graph in no. 1 

Please help me out to clarify the above matters. My work up to now is attached, may be very primitive. But I am trying to improve myself. (I am using LabVIEW 2013.) 

Thanks 

[fabio.int]

Hello, 

could you clarify your request better?

1. To take the difference in amplitude and plot a graph time vs change of amplitude 

Have you got two traces and you have to make the difference between the first and the second?

In this case you can see the attached picture.

2. How to derive an equation from the plotted graph in no. 1  

---

You can use the function that you find on Integration & Differentiation - Mathematics palette.

Best regards,

Fabio

[Nipuna]

Hi Fabio,

Thanks for your reply. 

1. Yes, I have two recorded sounds and I want to determine the difference between these two sounds. I am planning to do that using amplitudes by taking the difference of them. Then plot the graph time vs difference of amplitude.

Let say, First sound has an amplitude of "A" and second has an amplitude of "B". Now I want to measure these amplitudes separately and take the difference that is (A-B). Then I want to plot the graph time vs (A-B). Hope now clear for you. 

2.  I saw the attached picture. It has only one file path, but in my case, I want to compare two of them. Could you please clarify me this because I am still learning LabVIEW.

Thanks and Regards,

[fabio.int]

Hello,

I understand what you want to do.

When you use Sound File Read Simple VI, it gives you an ARRAY of channels that the file store. In your case you have an ARRAY which size is 1 (I suppose). The array element is a WAVEFORM. In this whaveform you find some informations.

Please, see the attached picture and I hope that it can clarify better.

Enjoy,

Fabio 

[Nipuna]

Hi Fabio,

Thank you so much for your guidance. I tried the way as it is in your attachment and I plot the result in a waveform graph but the amplitude difference is higher than the normal. Please have a look I am attaching them. The waveform graph 3 is the one I got from the way you told me and the waveform graph 2 shows the difference in amplitude measuring after the FFT spectral measurement. 

Also, I want to know why there are red and white in colour signals presence in graphs N0, FD0 and their respective FFT graphs.

Could you please clarify me on this. 

Thanks

[Nipuna]

Hello Everyone,

I am new to LabVIEW, please help me to clarify the following.

1. I want to compare the two signals and plot the change of amplitude in Y axis and time in X axis. 

2. I don't know the reason for red and white colour signals in the same plot as shown in png. 

Please clarify me these.

Thanks and Regards

[fabio.int]

Hello,

I don't have enough information about your application (how do you record the trace, what kind of mic you use and so on). But from the png I can understand that in your files there are almost two traces. For this reason you see a white and red plots.

For the "difference" unfortunatelly I don't have enough information on the process. What is your target? why you have to make the difference. Are you on the time domain? 

I attach a VI that show you more than one plots in the first waveform graph, in this way, I hope, you can understand what I want to say in the first part of this answer.

I hope this answer may help you. Best regards,

Fabio 

[Nipuna]

Hi Fabio,

I am unable to open the VI since your version is newer, mine 2013. Could you please send me it again. 

Basically, I want to identify the different acoustic signatures of a motor when it changes its loading condition. Sometimes when we are loading the motor there is a point at which motor is going to stop. I want to set a notification before motor stop. 

I thought of checking the amplitude in different loading condition and compare with the normal running condition. To do so I checked the amplitude in the time domain but in the frequency domain is better to identify the amplitude w.r.t to frequency. I recorded the sound using a mobile phone as a start, thinking to have hands-on experience with LabVIEW.  

Could you please advice me because now I am stucked. I need to do following,

1. Plot the amplitude of the recorded sound (time vs amplitude and time vs frequency) 

2. Compare two sound signals best suitable method to identify the difference of two sounds.

3. Plot a graph showing the difference of sound signals against the same time as before.

4. Derive the equation of the plot 3

I have attached a picture for clarification. 

If you can I appreciate your help.

Thanks 

[fabio.int]

Hello,
in the VI that I sent you there is nothing of important.

I found something that sound not good for my opinion. I'm agree with you that the "sound" of two motors (one good and one bad) are different, but if you analyze in the frequency domain it is better. The two files that you want to analyze are not syncronized that means that it doesn't make sense to do the difference. (suppose that you acquire two times the same motor. are you sure the two traces are syncronized and in phase? - see attached file)
What I suggest to you is to use an accelerometer (chipper than a mic) define a good position where to put it on the motor and make a frequency analysis on the good motor. You can define a mask around this spectrum. When you analyze others motors you can put the accelerometer on the same position and check if the spectrum match in the mask.
I made the same application for one customer's of mine.

best regards,

Fabio

[Nipuna]

Hi Fabio,

Thanks for your comprehensive answer.

 I understood your point using an accelerometer. But my aim is not to introduce something already exists. The selection of motor is only a start and a trial before proceed with my work. 

Synchronization is really a valid point that you highlighted. Even though, the signals are not synchronized amplitude of the signal should be in a specific range. Cant we measure that as I suggested in my previouse drawing. 

If you could please advice me on following.

1.Removing that red signal from the waveform plot?

2. Option to synchronize two signals or match the phases

3. Plot graphs as shown in my last hand written png

Thanks a lot for your continues guidance. I look forward to learn more from you.

Cheers