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Issues using more than 16 channels in daqmx

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I have put together a .VI (from bits and pieces from help on the forum) that I use with the USB NI-6225 to collect and record anywhere from 1-30 or so voltages from different 4-20ma transducers (pressure, linear, voltage...etc). I tried to set up the .VI to make it user friendly so that a person could name each channel, as well as setting the recording time and frequency (ie number of samples).  After the data has been recorded, the .VI outputs a timestamped TDMS file, a timestamped LVM file as well as a timestamped LVM file for an average of all the voltages on each channel.  


The problem I have noticed is whenever I have more than 16 channels activated, the recorded values for voltages on channels 17 and higher are erroneous.  For example, channels 1-16 output voltages from 1.0 - 5.0 volts (which is expected) and channels 17-30 are negative or very small (0.100 volts).  I know that the USB NI-6225 works properly because I created a simple .VI that uses just the DAQ Assistant to ouptut 30 channels onto a waveform graph and all channels read in the range I am expecting (1.0 - 5.0 volts).


To me, it seems that there must be something in the DAQmx (as opposed to DAQ Assistant) I am using my .VI that is causing issues whenever I try to record more than 16 channels.  I just don't understand labview enought to figure out what is possibly causing this issue and I was hoping someone could point me in the right direction

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Also, I wanted to add that whenever I use a simulated USB NI-6225 from the Measurement & Automation Explorer this problem does not show up and all the channels output expected values.  It just seems to only be a problem when I use the "real" USB NI-6225.

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Accepted by topic author MCHammer

Since you did not attach the working program, it's impossible to say what you have done differently. In this program, you do not specify the input configuration (i.e. single ended or diff).


p.s. The program is in bad need of major cleanup. Keep the program to one screen. Simplify.

Message 3 of 6

Sorry for not attaching my working program, but here it is. Like I said its just a simple DAQ Assistant setup for 30 channels and wired to a waveform graph.  This is just a barebones program without any of the channel setup and file output bells and whistles.  I just wanted to make an alternate program to troubleshoot the USB NI-6225 and see if it was working properly.  When I run this VI while all my transducers, it shows all of my output voltages in the proper expected range.  I used this fact to deduce that something must be wrong with the programing in my original .VI.


I know, I program is quite the mess and I was kind of embarassed when I had to post it on here for help.  I am still learning...thanks for the helps folks.

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Message 4 of 6

As I said, you are not expressly setting the input configuration. Add that to the DAQmx Create Channel. And create a VI with just the DAQmx functions and a basic channel constant instead of all that complicated code for creating the channel list.

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Yes, the problem was that I didn't specify the input configuration.  I put a single ended constant on the box and it worked like a charm.  Thanks for your help

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