How to find when a waveform crosses a certain amplitude

[srgray]

All,

I've got a waveform that I've saved from a TDS3034B oscilloscope. I'm trying to write a VI to anaylze this waveform. I'm specifically interested in finding the time (X value) when the waveform passes a certain voltage (Y value). I've used "Basic Level Trigger Detection.vi" and this works well to find the first occurrence. Is there a way to find the Nth occurrence? Or do I have to modify the waveform (chop off the part before the first occurrence) and search again?

Thanks,
Stephen

[Dennis_Knutson]

You can modify the Basic Trigger Level Detection. Look at the block diagram and you will see a control called 'max number of trigger points'. This is a hidden control so first make it visible. Do the same with the 'number of triggers detected' indicator. There is an array returned from the CLFN that is indexed to get element 0 and then converted to trigger index or a releative location. Instead of indexing only element 0, perform the operation on all elements of the array. Be sure so save the modified VI to a new location with a new name.

[Grayham]

There is a VI under Waveform --> Analog Wfm --> Search

This VI searches waveform data for occurances of a certain Y values and returns an array with the corresponding X values.

[srgray]

Thanks for the response. I'm having trouble saving that VI (Basic Trigger Level Detection.vi) as a new VI so that I can edit it. It's part of a polymorphic VI (which I'm not familiar with editing/creating). When I save a new copy, it won't allow me to edit it (there are no protections set on VIProperties->Protection). Any help?

Message Edited by srgray on 10-19-2007 11:42 AM

[lmtis]

Hi Stephen,

How did you try to save it?  I selected one of the two vis and saved it with a new name and location.  When I opened it I could edit it with no problem.  I thought I might have a problem because I don't have LVPro, just LV7.1 Full Dev.

[Dennis_Knutson]

That's how I just saved it because I happened to be using 7.1 at the time. I think 8.x is much different because the VI is in a protected vilib. I'm still learning 8.x and there must be a way to disconnect the link between a VI and the vilib but it's not immediately obvious to me. Anyone with more 8.x experience is welcome to chime in.

[srgray]

OK, I'm able to save/edit it now. Here's what I did:
Labview 8.2
-Drop VI on block diagram
-RightClick and select which one of the polymorphic VIs you want (Select Type)
-File->Save As


I'm not sure what I was doing before, but the Save As option wasn't available. Maybe because I wasn't selecting a Type first???

Thanks for the help, all.

-Stephen