Multiple Channel analog input scanning problem in USB6210

[sathya_tce1]

Hi Everyone,

                  I am using USB-6210 for performing some power measurement. Before using the board for real time measurements, I performed few test runs with following configurations. Here is my setup details.

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1. Two independed DC power supply outputs are connected directly to AI0( connected to Power supply 1) and AI1 ( connected to power supply 2)

    ( differential mode, so used AI0-8, AI1-9).

2. Power supply one is configured with 1.5v and power supply 2 is configured with 2.9 v

2. DAQ is connected to centos5 running Daqmxbase3.3 driver.

3. I tested the channel outputs with example contAcquireNChan available in /usr/local/natinst/nidaqmxbase/examples/*

4. I was expecting continous values of 1.5 as AI0 output and 2.9 as AI 1 output 

5. But its not behaving as I expected. Some times it gives 1.5 and 2.9 and other times it measure some junk values like (0.05. 0.6, etc)

6. When I searched about it I found that we need to10K resistor from "negative input" to DAQ ground ( Since I am dc ).

7. Now, My question is, I have two sources.Which source negative I should choose ?

[HeatherBaker]

You will need the resistor only if your power supplies are not grounded as explained here.  How often do you receive "incorrect" values?  How many samples are affected?  Is this behavior consistent?  Does it resolve itself or you make a change?  This information will provide us a little more insight into the issue.  Screenshots are always helpful if possible! 

[sathya_tce1]

Hi,

    Thanks for your reply. I understand that we need to add a resistor. But I have many independent sesnor outputs connected to different analog input channels. So , I am confused about which sensor negative terminal should be connected to the DAQ ground  with 10K resistor.

[HeatherBaker]

Each sensor will need to be referenced to ground as described in the manual.  Since there is only one AI Ground for the device, it might be cleaner to use a breadboard as an intermediate step.