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DAQmx configuration and terms used when configuring for signal acquisition



I have started using NI Daqmx  driver acquire analog signal using labview. 


I am finding bit difficult to understand the configuration to make when we are acquiring the signals.

can any one suggest is there any online simulator i can try to understand the concept of data acquisition.


and also any input for below points. 

1. Difference between Sample rate and Sample per channel(in DAQmx Timing (Sample Clock).vi).

2. Where are the other optins used.(handshaking,Implicit,use waveform..) in DAQmx Timing vi.

3. What is the significance of "Number of samples per channel" in DAQmx Read (Analog 1D DBL 1Chan NSamp).vi


I am trying to understand how sampling a signal affect by changing the above values.






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why we need to created virtual channel or task when acquiring data. 

what will happen when we create virtual channel.

which memory used (RAM ..etc) when data sampling is process till reading samples.





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Sorry to put question on top of this.


Is PXI chassis or daq modules have built in memory unit to hold the sampling data or our PC itself as to store/hold the sampled data.


when i creating the virtual channel, i have given only one channel as input , but when i reading the samples i can specify this as Nchan 1Samp or Nchan NSamp . How it is possible.




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I think if you do a Web Search, you can find NI's excellent set of Tutorials "Getting Started with DAQmx".  Spend a few hours carefully reading these.  I especially recommend the series on Basic Programming with NI-DAQmx.  I also recommend that you do not use the Dreaded DAQ Assistant, but instead read "Getting Started with NI-DAQmx Programming in LabVIEW", especially the White Paper "Learn 10 Functions in NI-DAQmx ...".


Once you read these, thinking about your questions, I think you will find all the answers, and more.


Bob Schor

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I had started to write a few short answers to specific questions to augment the excellent suggestion from Bob_Schor, but then realized that most of them won't help much until after you follow his advice and have some background material and context to work with.   In the process, you'll probably have already answered many of them yourself.


There's just one thing I'll address because I've seen it be a point of confusion for several other posters.

Even though the phrasing is very similar, the meaning of the "Samples per Channel" inputs are very different when calling DAQmx and calling DAQmx


When calling DAQmx Timing and specifying Finite Samples, it's used to set the actual size of the data buffer in system memory.  (Surprisingly, when doing Continuous Samples, it's generally ignored.  The buffer size is set automatically according to these rules.)


When calling DAQmx Read, it's used to determine how many samples to retrieve from the system memory buffer on that one specific call.  A common practice for Continuous Sampling tasks is to read about 0.1 second worth of samples at a time, which you can calculate from (Sample Rate / 10).



-Kevin P

CAUTION! New LabVIEW adopters -- it's too late for me, but you *can* save yourself. The new subscription policy for LabVIEW puts NI's hand in your wallet for the rest of your working life. Are you sure you're *that* dedicated to LabVIEW? (Summary of my reasons in this post, part of a voluminous thread of mostly complaints starting here).
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