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Split Signal after reading signal using daqmx read vi for multiple channel




I am using DAQmx read vi(Analog 1D Wfm NChan NSamp) to read single ended multiple analog input channels.After reading,I have to process two signals separately which I am doing with Split Signal vi. But, I am getting unexpected outputs in the case where I am not giving input to one among the analog input channel.I am attaching screenshot of that part of the vi for reference.Can anyone help me in identifying what I am missing...


Thanks in advance,


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Message 1 of 4

Use Index Array instead of Split Signal.  This way you can keep the waveform data types.


Hard to say what else you are having problems with without more details.

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Message 2 of 4



I tried with the array index also.Observation is same.I am trying to explain more about the setup and my observation below:

Device : NI USB-6218

Wiring : Two separate analog inputs are wired to ai0 and ai1.

Labview Code: using DAQmx 1D Wfm NChan NSamp) read two channels and analyze it to get the frequency and amplitude.


Input : ai0--->2V,1KHz Sine Wave and ai1 ----> 1V,2KHz Sine wave


Case (i) :  Reading from channels ai0 and ai1

Output : ai0--->Amp = 2V,Freq = 1KHz and ai1 ----> Amp = 1V,Freq = 2KHz

Expected Output : Same as above

Case (ii) : Reading from channels ai0 and ai2

Output : ai0--->Amp = 2V,Freq = 1KHz and ai2 ----> Amp = 2V,Freq = 1KHz

Expected Output : ai0--->Amp = 2V,Freq = 1KHz and ai2--->NA

Conclusion : ai2 is replicating the input in ai0 even when there is no input given in ai2. which is not expected and WRONG.


I am attaching the vi for reference.




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Message 3 of 4

Why did you use "Split 1D Array".  That is very odd thing to do.  You were supposed to use Index Array.


Are you sure you are reading the correct channels?  You are talking about reading 2 channels, but mention AI0 AI1 and AI2.  Your VI shows AI1 and AI2.


You say you are reading AI2 when nothing is hooked up to it, and it is duplicating another channel.  You have heard of "ghosting" haven't you?  When you have nothing hooked up to a channel, it is going to tend to look like another channel.  It is such a high impedance input, that there is no circuit there that is going to drain the charge off of the A/D converter and thus it is a "ghost" channel that is going to look like the previous channel just read.  You should wire a jumper across the input and the ground on that channel so that it will be a solid 0V and not floating like it is now.

Message 4 of 4