Any methods to find the envelope of this waveform?

[Bill Choy]

Hi,

I'd like to know are there any methods to find the envelope for this signal?

Bill

[chrisger]

hi there

the method using the Hilbert-Transformation won't work well because of the quality of the data (sharp edges, difficult to apply a window). But a simple Data-Reduction shows quite good results. See attachment.

[Davino]

Chris,

Using this example file with data reduction and the Hilbert Transform, how do I change input to accept a text file of numbers (e.g., array)?

David

[chrisger]

hi there,

well, that depens on the format of the text-file! if its a plain spreadsheet file you should be able to use "Read from Spreadsheet File.vi" from the File I/O - Palette. Be sure to provide a correct value for dt.

[Davino]

When I a connect the Read from Spreadsheet File.vi, I recieve an error (see attachment).  Is there a way to convert the data to the right type?

[chrisger]

hi there

you have to specify the format of your spreadsheet file. we can't interpret the files contents as long as we don't know where's the data.

to create a waveform use the "Build Waveform" Function from the Waveform palette and connect Y, t0 and dt. Y, to and dt must be read from your file or interpreted from the file's data.

[Davino]

I modified the above VI.  From the attached VI and associated data file, I want to draw on the graph a line through the reduction data points of the curve (or envelope) from -10 to -30 dB (on the Y-axis) and then extrapolate the line down to -60 dB.  What would be the best method to do this?  Also, when I converted the spreadsheet data to waveform, how do I specify that I want the time to start at -0.25 instead of 0?  Whenever I inserted a negative number into the t0 input on the "Build Waveform" vi, I recieved an error.  As an alternative, I offset the x-axis in the graph by right-clicking the graph and changing it manually.

[alexg123]

Hello Chris I think the your sample vi 

Envelope LV7.1.vi (72 kb)

 is great, can you help with finding the envelope of a waveform on the bottom side of the wave ..thanks Alex

[chrisger]

well, just invert the data Y before and after the transformation....

[FReich]

I have a similar problem,

I want to measure damping by acquiring the damped vibration response.

In order to do so I would need to get information about how fast the signal declines that means, that I need the peak value of at least two defined oscillation peaks within the signal. All peaks are on the envelope but I need to know where they are.

Any help greatly appreciated

Yours

Franziskus