calculate envelope curve x spacing

[myra]

Hi,

I have a sinusoidal voltage signal where the amplitude changes with time.  I want to determine the amplitude's dependence on another variable, so I need to separate out the oscillatory information.  I tried using the calculate envelope curve function, but the x channel spacing is not equidistant - you can't combine the x and y channels to make a waveform channel - so I don't know how to compare these channels with my other data (i.e. using regression). 

It seems that the envelope function goes through the data set and selects out all of the extreme points, divides these between upper and lower bounds, and puts these data points in the new channels.  Is there some function that would allow me to set up an x channel with equally spaced points, and interpolate the corresponding values for the envelope?

I tried using a curve fit to approximate the amplitude data, but it doesn't retain enough of the features.

Thanks, Myra

[Adam G]

Hello Myra,

I am a little confused on why you can't use the envelope curve function. You can change the spacing between the points by chaning the Interval size as a % of the x-range value. If you make this value smaller it will more closely follow the curve. Please lte me know if I am misunderstanding what you are trying to do. Have a great day!

Best Regards,

Adam G  

[Brad_Turpin · Accepted solution]

Hi Myra,

It sounds like the key issue you're facing is that you have one curve with non-equadistant X values and a second curve with equadistant values, and you want to compare the Y values of those 2 curves at exactly the same X values.  This is what the "Linear Mapping" function in the ANALYSIS Curve Fitting palette does.  Just provide the X and Y channels of the non-equadistant curve in the first two dialog fields and the X channel of the equadistant curve in the third field.  This will create a linearly interpolated version of your non-equadistant curve that has exactly the (equadistant) X values as your other curve.

If your equadistant X value curve is a waveform, then you'll need to first use the "Numeric Channels <=> Waveform Channels" function from the ANALYSIS Channel Functions palette, in oder to create that X channel you'll need in the third dialog field as described above.

Ask if you have further questions,

Brad Turpin

DIAdem Product Support Engineer
National Instruments

[myra]

Hi Brad,

Thanks, that seems to be exactly what I was looking for.  I found the linear mapping function last night, but I wasn't sure how to use the interpolate channel - so you filled in the gaps for me. 

There's another issue I have in diadem that I've been working on with tech support that I would like to ask you about, however I'll start another post for it since this one has been resolved.  It's about the joint time-frequency analysis tool... hopefully someone on the board has more experience using it than me! 

Thanks, Myra