Raw 1D DAQmx

[labmaster]

I intend to acquire data so fast in Labview 8.6 by DAQmx.

Usually, I have used 2D DBL Read function for 2 channels analog inputs.

Because of limited (buffer and hardisk) memory, I would like to use 2D integer Read function.

1) When I use integer function, can the limited (ultimate) speed be increased?

2) How about speed advantage in using Raw 1D integer function?

1D doesn't include the channel information. How to recognize the channels and each points in 1D array?

Does it serialize like 0ch 0pt, 1ch 0pt, 0ch 1pt, 1ch, 1pt.... 0ch n pt, 1ch npt?

labmaster.

[Dennis_Knutson]

There is no such thing as unscaled 1D integer data. Your only options are 2D unscaled. Even if there was a 1D option, you would be transfering exactly the same number of bytes if you had multiple channels and multiple samples.

Obviously, there is a storage advantage with integer data. A DBL is 64 bits whereas you can use 16 bit integer if your DAQ card has an A/D with this or fewer bits. If you ever change to a DAQ card with greater resolution, you might want to use a 32 bit type. With integer, be sure to save the polynomial to convert to scaled data. While I'm sure there is a speed advantage, I'm not sure of what the actual numbers might be. You might want to do a search to see if some benchmarks exist.

[Jordanyorg]

Hey Labmaster,

Did you ever find out how to extract channel information for multiple channels with raw 1D data?

Thanks,

Jordan

[Dennis_Knutson]

It's unscaled 2D data and the help for the functions explains how the data is arranged. To quote: "data returns a 2D array of 16-bit signed integer samples. Each row corresponds to a channel in the task. Each column corresponds to a sample from that channel."

[Jordanyorg]

Maybe we're not on the same page. I'm looking at the polymorpic DAQmx Read vi, with the selection More.Raw.1D I16. I have my task configured to look at multiple channels. The output from the VI is a 1D I16 array. It looks like the channels are interleaved, but I just want to make sure.

[Jordanyorg]

Just confirmed that the they are interleaved.

[Dennis_Knutson]

Never saw that before. Only saw the option for 2D under analog read. Think the 2D option might be easier to use where you simply index a row for each channel.

[Jordanyorg]

Do you think it would log any faster to just use the raw data?

[Dennis_Knutson]

Yes. Do you know that the latest version of DAQmx can be configured to directly stream to a TDMS binary file? What version are you using?

[Jordanyorg]

Yes. I just found the property nodes for that this morning and will be looking into it. Thanks for your help.