Set Dynamic Data Attributes zeros waveform t0?

[MikeyC]

Hi -

A labview newbie here, so please be gentle 😉

I have a simple setup using mainly express VIs where I am performing the following steps within a while loop

1) Collecting signals with DAQ Assistant, which outputs Dynamic Data. This is collecting N samples

2) Editing the attributes of the Dynamic Data using the "Set Dynamic Data Attributes" express VI

3) Storing the revised dynamic data in a file using write to measurement file.

The problem I've been seeing is that whenever I insert the "Set Dynamic Data Attributes" express VI within the data stream, I end up with a file where the signal timing (i.e., t0 of the waveform) has been zeroed out. This seems to happen no matter what attributes of the dynamic data I edit. For example, even if I just try to set the signal name I end up with the output having a nulled-out t0

FYI, I'm using Labview 2009 9.0f3, 32-bit

I've attached a simplified code demonstrating what looks like a bug to me. Any help would be much appreciated!

[Dennis_Knutson · Accepted solution]

It looks like a bug to me as well. Also, unlike other Express VIs, you can't right click on it and select Open Front Panel to see what is wrong. It's pretty simple to come up with a work around. I converted to a waveform, got the t0, and passed that back as the timestamp for the slected signal.

[David_L]

Thanks for pointing this out to us.  I have filed this under CAR # 236174.  You can check the release notes of future versions of LabVIEW to see if this has been fixed.

As for Dennis' great workaround, I put it in VI form in case it was not clear.  

[MikeyC]

Thanks to you both for the quick and informative replies! It's good to know there's such a friendly and responsive community out there, as I'm sure I'll run into more problems during my first project 😉

I've dived a little bit deeper into Labview now, so I've switched from the express VI's to actually using DAQmx tasks and outputting waveforms instead of Dynamic Data. So far I haven't run into any troubles with any of the waveform functions but I'll be sure to post again if I see any other strange behaviors.

Thanks again,

Mike

[MRH]

Just hit the same problem. Found this thread.

I may be being dumb, but can't see a way to get this to work with multiple channels of data.

I've had a go (see attached) and:

If I don't use the t0 workaround, then signals are OK but timing wrong

If I use t0 workaround but only for channel 0, then I get only one signal

If I use t0 workaround for all channels, I get the right t0, but lose the data.

I've put some switches on the front panel to turn the t0 thing on and off.

Any suggestions would be very gratefully received. Many thanks.

[ABingham]

When will CAR # 236174 be fixed?

It pretty much makes Set Dynamic Data Attributes useless.

[Zachmx]

Hi ABingham,

CAR # 236174 is scheduled to be fixed for the LabVIEW 2012 release.

[Machine_Builder]

So, it's 2015 and I seem to be having this exact same problem.  The solution shown works for one channel, but then I loose the other channel.  I'm running Labview 14.0.1  Has this been fixed in an update or new release

Is there another "simple" work around?

Thanks in advance.

[RavensFan]

Loose = not tight

Lose = not found

You say you lose the other channel.  Why is that?  Did you try the VI shown in David_L's message?

Attach your VI and we can debug it.

If you convert the dynamic data containing multiple signals to an array of waveforms then you can iterate through the waveforms in a For Loop to set the t0 value.

[Machine_Builder]

Thanks for the spelling tips. 🙂

I've attached two files.  This vi is basically doing what I need it to do with the exception of having to select between either no time stamp (first row is correct all subsequent rows are the 1904-01-01 deal with all zeros for the time) or "untitled" as the column labels in my measurement file.  Any other tips would also be appreciated. 

The vi with "no time stamp" in the title is how I was assigning the signal name to the channels.  When I probe the wire before and after the "set dynamic data attributes" it is clear that the time stamp is being lost.  No combination of settings that I tried on the function set attributes express gave the desired result.  The vi with "lost channel" is where I implemented the "t0" fix referenced in this thread.  By "lost" channel I mean when I probe the wire I only see the data from channel zero. (I had to remake this vi for this post since I never keep a copy and I can't test it at the moment; hopefully it is the same as my previous attempt.)

Thanks again.