Large offset values for NI 9222

[wmm26]

The initial readings on select channels of my NI9222 and NI9220 DAQ modules are significantly offset from the expected 0V value that I observe (within a reasonable tolerance) on the remaining channels.  My DAQ set-up is composed of 3 modules (NI 9403, NI9222, NI 9220) that are connected via a NI 9188 chassis.  I am testing my set-up with all the modules connected and without hooking up any of the respective AI+/- pins.  I attached a screenshot of a test that I ran on the NI 9222.  Below is a list of all the initial readings for my DAQ modules.  I listed the channels with the large offset voltage that are causing me concern in bold.

NI 9222:

ai0-  10.6 V

ai1-  10.6 V

ai2-  1.97 V

ai3-  0.29 V

NI 9220:

ai0:    -0.002    V

ai1:    -0.003    V 

ai2:    -0.0005  V

ai3:    -0.002    V

ai4:    -0.009    V

ai5:     0.0004  V

ai6:    -0.0005  V

ai7:    -0.001    V

ai8:    -0.003    V

ai9:    -0.001    V

ai10:  -0.004    V

ai11:  -0.004    V

ai12:  -0.009    V

ai13:  -10.47    V

ai14:  -0.002    V

ai15:  -0.010    V

Any information on why this might be happening or how I can resolve this issue would be much appreciated.

Thanks,

Max

[FuManWho]

Hi wmm26,

Have you tried writing a value to these values? Use a multimeter to distinguish the value going in versus the value you are observing in MAX.

Also have you tried using a mulitmeter to measure the input values?

Also have you tried resetting these devices as well?

Have you tried swapping the slots which each module is in?

[wmm26]

Hey Paolo,

I was able to resolve this issue.  The step that helped me was using an oscilloscope to compare measurements that I observed using the MAX.  I assumed that the ground from the power supply would be used as a default internal ground.  Connecting the AIO- terminal to the grounded end of my oscillascope was a sufficient reference to re-calibrate my channel readings at 0 volts.  I found it odd and slightly alarming that only certain channels exhibited this feature and at different levels.  Why is this the case?

Max

[FuManWho]

Hi Max,

It seems that the 9222's channels are floating relative to earth ground as they channels are isolated from each other. 

I found it in the specification sheet found here:
http://www.ni.com/pdf/manuals/374223b.pdf

We recomend you ground these channels with the ground used for the devices in the "-" terminal as the measurements that are expected is differential.