2D array to waveform graph

[owlowl]

Hi,

I have a callback library node which returned a 2D array of size (2 x 100). This node is a data acquisition program which acquired 2 set of data of 100 points from 2 different channels. I would like to know how can i get the time of each of these 100 samples (they are of fixed sampling interval)? Do i need to do it in the data acquisition program OR can i do it in labview using the time-stamp vi to get the start of the acquisition process?

I am trying to send these 2D array and time stamp to a waveform graph. How can i combine them?

Thanks

wee

[Philip_Courtois]

I assume that you are not getting any timing information back when calling the DLL.

You can use the �Get Date/Time In Seconds� function next to the Call Library Function Node to register when the DLL was called.

Use the �Build Waveform� function to bundle the start time (t0), the sampling interval (dt) and the data array into a Waveform data type. You can then display this by using a Waveform Graph.

See the attached �TimingInfo.GIF� for an explanation.

Best regards,
Philip C.
Applications Engineer
National Instruments

[owlowl]

Hi Philip,

Yes, assumption is correct.

Thanks for your picture. However, i remembered that I have tried something similar last week, the error was that the "Y" can only accept a 1D array. I have not figured out how to change it to acccept a 2D array which i am planning to input. I am not sure where to change it.

Thank you.

wee

[Philip_Courtois]

Remember to allocate the memory in LabVIEW before calling the DLL. See the attached image where the we allocate a size of 2x100 to the 2D array.

Best regards,
Philip C.
Applications Engineer
National Instruments

[owlowl]

Hi,

Sorry for this late reply.

I have tried the suggestions. But i encountered a problem. Even after i have initialised my array to 2D, the Build Waveform function still gives me the error of 2 different sized arrays connected.

I have posted two snapshots (jpeg format) of the "before i connect the 2D array to the Build Waveform" and "after i connect the 2D array to the Build Waveform". I am not sure where did i go wrong.

I am sure that i have a 2D array as subsequently in the vi, i have used the Index Array function to obtain the respective elements of in this array.

For another question,

This same 2D array is (8x1). Can i use a waveform graph to display 8 different points corresponding each elements on the same x-value (8 vertically plotted points)? I have tried and connected this array to a waveform graph but it produced a single point only. If i were to transpose this array, I get 8 points but on different x-value (1 point on x=0, 1 point on x=1 and so on).

Thanks a lot

[owlowl]

it seems that i cannot post two attachments at the same time... Is there a way to do it?
cheers.

[tst]

Posting more than one attachment?
mmmm...
Well, you could travel back in time to the old forum system.
And if that solution isn't good for you, compress the files into a ZIP file.

[owlowl]

i just thought that there is a special way to do it as it is pretty common in other websites.

Thanks for your answer

cheers

[owlowl]

Hi,

By the way, I have solved my problem of getting a 2D array (8x1) onto a waveform chart with time stamp using "build waveform" and "bundle".

Cheers