Indexing data on a for loop to overlay data on a xy graph

[edmiles55]

I am using express VI's to measure both voltage and current data in a For Loop. I want to plot a current vs voltage graph but have each iteration of the loop overlay the others as if it were its own independent data set. I have been unable to bundle the data and convert it into a xy graph because of the number of elements, 3 for the bundle and 2 for the graph. I need a method to index the dynamic data wires so that I can overlay them.

[Caseyw]

The x-y graph expects either an array of clusters (xy values) to be wired in, or a cluster containing an x array and a y array. For multiple plots, the x-y graph expects an array of clusters containing an x array and y array each. You can think of each cluster as a "plot".

Since the x-y graph has no history (no buffer), you will need to keep all of the plot information around in each iteration of the for loop. This can be done using a shift register.

Each time through the loop, you can use the build array function to add an additional channel (an extra plot) to the x-y graph.

To obtain the x and y arrays that you will put into a cluster, you can convert from the dynamic data type into a 1D array of scalars. You can find this on the functions pallette under express, signal manipulation, from ddt.

I hope this helps. Please let me know if you need additional help.

Casey Weltzin
National Instruments

[JLS]

Hello,

After reading the thread, it sounds like you're looking for a chart-like graph - I have attached an example with illustrates this.  Keep in mind that "graphs" in LabVIEW generally plot arrays of data (in the case of an XY graph, you pass a cluster which contains an X and Y array).  The example behaves like a chart by building an array one data point at a time (in this case both an X and Y array of course) on each iteration of a loop, and displaying the data at each loop iteration - this gives the look and feel of a chart which accumulates data.  It is attached in version 7.1 - hopefully you have that version or later to open it.  I have also attached a program which shows how to plot multiple data sets on an XY graph, in all 3 current formats accepted by the XY graph - it's attached in version 8.0 because the ability to plot complex data to an XY graph was added to version 8.0, and it illustrates this as well.

Best Regards,

JLS