PCI 6229 Multi Channel Analog Input Methods

[j.m.m]

Hi,

I just received this new board which I am trying to get used to and I am trying to read from two distinctive channels (0 and 6) in single ended mode within a C program.  I am running NIDAQmxbase for Linux (2.4.x kernel) and I am trying to perform multi channel acquisition without any luck.  All it does is output roughly the same value for both channels no matter how I try to do it.  However,  I am able to retrieve the signal value of one channel using the supplied examples (ie. acquireNScan.c).  Even when I use the multi channel example (contAcquireNChan.c) outputs the same value for both channels.  I have tried using various channels which are close to eachtother and some futher apart since I read up on possible "ghosting" issues.  What is the best way to collect multi channel analog values?  Is it possible to create a different task for each individual channel you want to read and then just perform a read for a respective channel using its respective task?

Thanks,

JM.

[AlanArmstead]

Hello JM,
I've got a few things to mention, as well as some suggestions.  First, how are you addressing your channels.  The syntax for multiple channels can be written a couple different ways.  "Dev1/ai0:5" will read from channels 0 THROUGH 5.  Whereas "Dev1/ai0, Dev1/ai5" will read from channels 0 AND 5.  Secondly, how are you grouping your input channels when they are read?  This is determined by the 'fillmode' input to the DAQmxBaseReadAnalogF64 function.  Also, what are you connecting to your channels?  If you don't have anything connected, then all the channels will float to roughly the same voltage.  If you short your analog inputs to ground, do you read 0V?  Additionally, there are some wiring considerations depending on what terminal configuration you choose (Diff, RSE, NRSE).  Here is a document on wiring and noise considerations.  Hope some of this helps!
-Alan A.

[j.m.m]

Thanks for the quick reply.  I ended up figuring out my problem.  I had it set in differential mode (which is the default)  when I was trying to do single ended.