create line from x-y graph live data

[Gaudier]

I am sweeping from -1000V to 1000V I am getting a characteristic curve I(V), I need the slope of the middle part of my curve. I can do it on a signal graph but not on a x-y graph. I need to do it on the x-y so I won’t loose the voltage values.

Anyone can help me create a line from 2 specific points from a live measurement on a x-y graph?

Gaudier

[altenbach]

Maybe you could do something along the lines of my earlier example. It does a linear regression of all points on an xy graph between two cursors.

See http://forums.ni.com/ni/board/message?board.id=170&view=by_date_ascending&message.id=280812#M280812 for details.

[Gaudier]

I already tried that, the problem is that I am taking 1 measurement per millimeter for 100 points in about 3 minutes and when I tried using cursors to create my lines they go crazy on  next measurement and  before  I could set them right  the next measurement is on.  On the attached vi I have what I need on a I vs.V graph but on the waveform graph.

Can I do what I’m doing on the waveform on a x-y?

Thanks

Gaudier

[Gaudier]

You can read the first 500 points of this sample so you can see the shape of my curve.

[altenbach]

Do you want the slope of the steepest part in the center? This is only a few points and won't be accurate because you also seem to have some oscillations in the data.

• Maybe you can filter it and take the derivative, then just find the max?
• How about fitting the entire central part to a sigmoidal function with a polynomial background, for example.