Multiple Analog Input using DAQmx data

[Alisterio]

Hi All! I have a very specific question about data processing.

I am currently trying to use multiple channels and measure them "simultaenously" (I know the machine doesn't actually do that). I have an initialisation (see attachment) that includes three AI ports and also a write data section (see attachment) that runs , writes/reads, and then stops the process.  

Now this is where I had problems understanding how the data is being read out, and so I know I am sure I am not aware of something.  

When I select in the DAQmx Read I then select  Analog > Multiple Channels > Multiple Samples > 2D DBL what exactly am I selecting? I expected three rows (From the three initialisations in the beginning) as an output but there are only two. So there is something I fundamentally missed. My purpose is to write finite data out from all the three ports using the DAQmx Read. 

So far all the readout I get from two of the ports give slightly the same signal, as I understand there is also "ghosting" happening ( a separate issue I believe I have resolved by adding the third channel before the channel with lower impedance). 

Note: I have looked at the following links quite a few times but if I missed anything that is relevant to this discussion please excuse my lack of observation. These ones were helpful so far but I just can't seem to find what I need to understand what is happening. 

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000000P8b1SAC&l=en-AU

https://forums.ni.com/t5/Multifunction-DAQ/How-to-use-DAQmx-Read-to-measure-multiple-analog-channels...

https://www.ni.com/en/support/documentation/supplemental/06/learn-10-functions-in-ni-daqmx-and-handl...

[Kevin_Price · Accepted solution]

Nothing jumps out as wrong.  You've configured your AI task to have 3 channels in it and when you call DAQmx Read (NChan NSamp), you should get a 2D array with 3 rows (one for each channel).

Not sure how new you are to this stuff, but is it possible that you're displaying the data in a GUI array indicator that only *shows* 2 of the 3 rows of data at a time? 

-Kevin P

[Alisterio]

Thanks @Kevin_Price ! It seems that I missed it when I was busy writing up my imaginary problem 😛 Thanks heaps. Appreciate the quick help!

[ashwini11]

I am trying to generate the signals through labview and access these signals using DAQ. I have attached the code and obtained results below. Why the signals are looking like that in oscilloscope. how to correct it?

[Alisterio]

HI ashwini11 as I am a new member I do not have much experience. After taking a look at your code I am not sure what to say. It will be better for you to start a new thread and explain your problem in detail. 

I have not worked with NIElvis so I definitely can help there.