Problem reading values above 2.36V with NI MyDAQ and USB 6008

[Reena]

Hi

I am simply trying to measure voltage across a resistance in a resistance divider using DAQ card. The input voltage is varied over a range of 0 to 10 volts and is provided to resistance divider through AO0 of NI MyDAQ. The voltage across R2 is read using analog input channel AI0+ and AI0-. The problem is

1. The resistance voltage is read perfectly within range 0 to 2.36V. As soon as resistance voltage reaches 2.36V, any voltage above this value is saturated and read as 2.36 V by MyDAQ.

2. I also tried reading the current through a single 1k resistance using the DMM on MyDAQ but the current also shows saturated after the same value of 2.36V .

3. The inputs are working fine if i directly connect the analog output to the analog input or through a single resistance. 

4. Similar observations were observed with USB 6008.

I really fail to understand what I am doing wrong here. Please help as it is really urgent.

Thanks and Regards

Reena

(CLAD Certified)

[Reena]

I have also tried giving input from USB-6008 DAQ card and from digital 5V to resistor divider and then reading AI from MyDAQ. This works fine. What I can foresee from here is that there is some grounding issue. May be the AI are internally connected to AGND of AO also and that is posing the problem. But using two different DAQ cards for such a small problem does not seem to be an appropriate solution to me. Please guide if anything can be suggested in the same respect.

Thanks

Reena