X-Y Graph Question

[unclefeezus]

Hello All,

I'm reading in two channels of data from a SR830 lock-in amplifier, and trying to plot X vs. Y. I can display both X and Y on a waveform graph, but for some reason when I plug both X and Y into "build X-Y graph" nothing shows up on the front panel. Strangely, if I change the values of X and Y via the lock-in amp the graph's axes scale. Anyone know what's going on?

Regards,
Danny

[NIquist]

You may be only displaying a single point which won't be visible unless the point style is a dot.  Click the plot legend and select a point style besides the default (none).  If you see a point then, you're just not sending an array of data to the graph, only one point.  post your code if you need more help.

[unclefeezus]

Thanks for your help. You're right, it does only show one point. How do I turn two realtime streams of numbers into an array that will display a meaningful x-y plot?

I'm not sure what you mean by "code" (I'm very new to labview), but here's the part of my schematic that I'm using. Sorry, it's a little messy, but the basic idea is that it recieves two numbers on two different lines from a serial port, then splits the string, converts them into floats, and then feeds both those numbers directly into the plot.

[NIquist]

Do you really need to plot X VERSUS Y, or do you just want to graph two channels of data?

If #1, then you will need to enclose your code (in LV, the block diagram IS the code) in a while loop and use shift registers with the build array function concatinating the data on each iteration.  The continously updating arrays are then wired to the graph.

If #2, then a waveform chart would be more appropriate.  You can just wire the floats into a chart because it stores a history of data points.

In either case check out some of the shipped examples for charts.  Help>find examples> Building User Interfaces>Displaying Data>Graphs and Charts.

I would also suggest you look for the LabVIEW style guidlines tutorials (search the forum) because your code is making me hungry... FOR SPAGETTI!

[Dennis_Knutson]

Actually, if it's #1, then a False constant can be wired to the Reset input of the Build XY Graph.

[NIquist]

Thanks Dennis,

I'm still using LV7 and miss these neat little tricks in the new versions.  Time to upgrade.

[Dennis_Knutson]

The Express XY Graph was introduced in version 7.0.

[NIquist]

HaHa, you're right!  I don't think I've ever opened the express palette.  I always convert those VIs as soon as I see them.  I like knowing what's inside and how they work.  I used to drive my Mom nuts by taking apart every appliance in the house.  Some things never change .

[unclefeezus]

Yep, that worked. Thanks everyone.

Danny