ni pci 6036e

[dianek]

I am using simulink with a real time windows target, interfacing to my process with a ni pci 6036e daq.  When I set up the analog input for just one channel, the signal that I read is fine.  If I enable  2 channels, and connect up a 2nd signal, the first signal seems to get a bit of a bias on it when the signal is on a decreasing slope.  I am using fixed rate sampling of 1000 hz.  I tried dropping the sampling rate, but problem persists.  I tried connecting up and using the ni measurement and data acquisition to perform the same test, and the problem goes away.  ???  Is this a matlab issue with the daq?

[GarPar]

Hi dianek-

     Did you mean to say that you checked the signals with Measurement and Automation Explorer (MAX)?  Then the errant readings went away?  What do you mean by bias?  Are you seeing ghosting (where one signal is reflected in another)?

     If you are seeing the correct behavior in MAX, then everything is setup as it should be.  MAX allows you to look directly at your hardware.  It removed software from the equation so you can verify raw voltages, signal connections, etc.  If you are seeing things correctly here, then that would point to your MATLAB code as the culprit.  Are you opening a test panel in MAX?  Setting up a task?  Are you running at the same sampling rate?

     I hope this helps.  Have a great day!