Index Waveform Function Bug

[JackHamilton]

The index wavefore VI has two modes for indexing the wfm.

1. By index of point

2. "Relative Time"

With Relative Time - you have to specific the time location to index - the bug is this must be ABSOLUTE TIME, meaning you can't wire 0.001msec - you have to take the T0 value and Add 0.001msec as the index value. :thumbdown:

This does not at all correlate with the ring text stating indexing by "Relative Time" it's Asbolute time.

Nag by Jack Hamilton

The wabbit hole goes deeper, sample wfms don't have valid timestamps!

See example code.

Download File:post-37-1112650773.vi

[Dan Press]

Jack,

You got confused by the waveform attribute function. That is designed to let you add custom data to your waveform wire. By specifying t0, you just created a new attribute named "t0". The waveform's t0 is not what you're editing. To do that, you use the Build Waveform primitive. It works just like the Bundle by Name.

This would be a good one for the old OC LVUG. I miss those!

Take care,

Dan Press

Certified LabVIEW Architect

PrimeTest Corporation

Download File:post-123-1112652875.vi

[JackHamilton]

Jack,

You got confused by the waveform attribute function.  That is designed to let you add custom data to your waveform wire.  By specifying t0, you just created a new attribute named "t0".  The waveform's t0 is not what you're editing.  To do that, you use the Build Waveform primitive.  It works just like the Bundle by Name.

This would be a good one for the old OC LVUG.  I miss those!

Take care,

Dan Press

Certified LabVIEW Architect

PrimeTest Corporation

4433[/snapback]

Dan, I know now the "Build wfm" is the function to use - I would challenge as to why "Wfm Attribute" would not be the most likely candiate? One could argue the t0 timestamp is an attribute of the wfm?

That said - that was not my initial Bug report - your code even reveals the bug! Look at the start timestamp of the Array subset it starts the same time as the original wfm - even though its wire to extract the sub-set 10msec from the start!.

I've posted this to the NI disucssion forums - and they come to the conclusion - its a bug!. You have to take the t0 - offset to and input that to get the subset start index to be correct.

Thanks for your input on this. I miss the meetings too!

Jack Hamilton