# LabVIEW

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## 2D DBL NChan NSample vs 1D WFM NChan NSample

I have a doubt on the difference between 2D DBL NchanNsample vs 1D WFM NChan N sample options.

When I used them to obtain analog input of multiple channels, both of them gave similar values in the output files, except for the timing information in DBL.The DBL has a  relative timing information dt of 1 and it scans each channel in a given sample clock to write a row of floating values for each channel.

My question why the WFM is called 1D WFM when it outputs various channel information similar to a 2D DBL

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Accepted by sharathnu

## Re: 2D DBL NChan NSample vs 1D WFM NChan NSample

Hi sharathnu,

why the WFM is called 1D WFM when it outputs various channel information similar to a 2D DBL

Because you get a 1D array of waveforms - or a 2D array of DBL values. Both contain the same samples, but the 2D array is missing ALL timing information…

The DBL has a relative timing information dt of 1

The 2D array of DBL has NO timing information!

Best regards,
GerdW

using LV2016/2019/2021 on Win10/11+cRIO, TestStand2016/2019
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## Re: 2D DBL NChan NSample vs 1D WFM NChan NSample

Hi Gerd,

Thanks.

Does that mean 1 D array function gets N number of 1-D array waveforms; each array corresponding to a channel?  (Eventually, you have a 2D array)

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Accepted by sharathnu

## Re: 2D DBL NChan NSample vs 1D WFM NChan NSample

A Waveform is a Cluster with three pieces of information:  t0, a TimeStamp corresponding to the time of the first sample; dt, a Dbl representing the time (in seconds) between the samples, and Y, an array of Dbls consisting of the samples.  The Array form of the data is the same as the Y component of the Waveform.  If you had identical DAQ devices collecting the data, the Array output from one would be identical to the Y-component of the Waveform output of the other.  As GerdW said, it would have the same data, but you'd need to "know" (or "add in") the timing information, which in most case is just "dt" (you usually need to know the sampling time, whose reciprocal is the sampling frequency, and in some circumstances, you may want to know t0, when the data were acquired.  The Waveform "bundles" these timing parameters with the data, Y.

Bob Schor

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