XY graph combined with intensity graph

[Frank Van Vaerenbergh]

Hi,

I've written an application that collects a trace from a Spectrum Analyzer and visualises this trace in an XY graph to see the actual spectrum measured. This routine repeats itself until the user stops. During this loop a waterfall diagram (i used an intensity graph) is build and grows with each retrieved trace. 1 trace holds 3123 values that is fed to the XY graph and to the intensity graph. The plot area of the XY graph and the intensity graph have the same width and are positioned exactly under eah other, so the x axis (frequency) can be used (visually) for the waterfall diagram.

When a peak appears on the XY graph that is continous, you should expect that this peak will appear as a line right under the peak in the XY graph. This is not the case. It seems that only a part of the data fed to the intensity graph is vsiualised, moving the line to the right in the graph.  The X scaling of the inensity graph is set to hold this amount of values.

Has anyone an idea how to solve this so the values in the intensity graph fall on the same X place as in the XY graph?

many thanks,

Frank Van Vaerenbergh,

Project Engineer

Rohde & Schwarz Belgium

[Evan]

Sounds like a great application.

Can you attach some sample code with data so that we can see what you are getting and help you get the actual solution?

[Frank Van Vaerenbergh]

Hi Evan,

I'll try to get a printscreen posted You'll get the idea. The code is not possible because the application is too big and classified.

Thx for the reaction.

Frank Van Vaerenbergh

[Frank Van Vaerenbergh]

Hi Evan,

Attched you find a printscreen of the user interface.

The 2 lines in the waterfall should be right under the 2 peaks in the XY graph.

The number of datapoints is identical for both graphs (3123 points)

If you have an idea how to solve this?

thx,

Frank Van Vaerenbergh

Project Engineer

Rohde & Schwarz Belgium NV

[VPS]

Probably a stupid question, but is your frequency axis linear scaled? From the upper graph it seems that you have more values at lower frequencies. This would of course result in such an effect

Steven

[Frank Van Vaerenbergh]

Hi Steven,

That was also my first idea, so have put the x axis mapping mode explicitly to linear but this didn't solve the problem.

thx,

Frank

[VPS]

Probably we are talking about different things.
I meant that the x values of your xy data should be equally spaced. So if you were to plot the x-values in an intensity graph, do you then get a straight line?

Steven

[Frank Van Vaerenbergh]

One thing i don't understand: I feed the same data (this is a global var that comes from my measurement process) to the XY graph and to the intensity graph. If there is a non linear spread in the data, the peaks still should be in the same place meaning, the line in the intensity graph should be right under the peak in the XY graph. It seems that the intensity graph visualises data differently than a xy graph. When i turn on the X scale, i see that the the same number of points are visualised in the intensity graph as in the XY graph.

Frank

[GerdW]

Hi Frank,

when you can't provide your original vi, why don't you provide a minimalistic example vi showing the described behaviour with some sample data?

[VPS]

"When i turn on the X scale, i see that the the same number of points are visualised in the intensity graph as in the XY graph."

For the intensity chart the x-axis is not defined. So the x-axis of your intensity chart is probably ranging from 1 until the length of your array (and not between 0 and 18000 as your xy chart)

Steven