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multiple channels (Analog Input) using DAQ.

Well, I would like to know how to get multiple analog inputs from a circuit and show their value. In the enclosed circuit I want to obtain in one daq the voltage "Vc" and in another daq the voltage "Vb".

In doing so there is an error indicating that we must use "Multiple channels" to do what we want.

We currently have 2 daqs with which we generate the voltage Vcc (5v) and Vbb (3v).



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Message 1 of 6

Hey Jose,


What hadware do you have ?

What is the exact error you get ?



CLAMaxime -- Kudos are a great way to say thank you
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Message 2 of 6

Hello jose,


some advices :

Use the data flow of LabVIEW to generate firstly then acquire your data.

Use error handling.


To acquire data on 2 channels by using DAQ assistant : at the end of the configuration, select the two channels that you want to have>then, use your graph to visualize datas of the two channels, you can use convert data (Express>>sig Manip) and choose 2D array if you want to see your data in 2 columns of an array.



Kudos are welcome!Smiley Wink


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What hadware do you have ?

National Instruments (NI USB-6008)


What is the exact error you get ?

the conflict is when using two analog inputs (DaqAssistant and DaqAssistant2)

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According to the error you get, yes you should follow Fred's advice above.

When you want to acquire 2 different channels at the same time, just "bundle" them under the same Task. You can do so during the configuration of your task by selecting two or more channels in the provided list. If you don't do that, then the second Task will try to access the device which is already use by the first Task and return an error.


Here is a document you might want to read :



CLAMaxime -- Kudos are a great way to say thank you
Message 5 of 6

I strongly recommend you spend a little bit of time and learn how LabVIEW works with DAQ (Data Acquisition) devices -- it does not involve the Dreaded DAQ Assistant (and its Evil Twin, the Dynamic Data Wire (both of which you have in your picture -- I'm not going to do my standard Rant about how I hate "pictures of Block Diagrams", and really want VIs to be attached ...).  Here are some recommendations:

  • Plug your Device into your computer.  Open MAX.  Find your Device.  Open Test Panels.  "Play with" your device to get some idea of how it works, what the choices are, etc.  Note for most Analog Input devices, you can specify multiple channels!
  • Read this wonderful White Paper about DAQmx.  Pay attention to the concept of Tasks.
  • If you are using LabVIEW Project (which I am guessing you are not), you can define your DAQ Tasks in Project.  Otherwise ...
  • Open MAX again, find your device, and Create Task.  You can create one Task for your A/D input, specifying the Channels, the Voltage Range, the input configuration (you should probably use Differential), and the timing parameters.  You can create another Task for Analog Output, Digital Input, or Digital Output.
  • Now you are ready to program DAQmx.  You need 3-4 DAQmx functions -- Start, Read (or Write), Stop Task (read the White Paper, it will explain).  Note that the Task In terminal of DAQmx Start is created by right-clicking the Task In terminal, choosing Create Constant, clicking the little Down Triangle, and selecting the Task you just created in MAX or Project (previous Bullets).

Using "real" DAQmx and Tasks instead of the DDA (Dreaded DAQ Assistant) will make your code "lean and mean", easier to understand and debug, able to be probed (tested) and flaws located/fixed, and you will have a much more professional piece of code (and will learn more about LabVIEW).


Bob Schor

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