DAQ device help

[jane6366]

I'm using BNC 2090A with USB 6366 Multifunction I/O device and I'm having trouble with some of the analog inputs. Certain Analog inputs have what seems like an offset voltage. I checked my ground reference on my BNC cable, and the center pin is reading zero volts relative to the shielding. I can switch the BNC signal to AI0 for example and it will read out zero volts as it is supposed to, but when I switch it to AI1, it reads 0.14V. Some channels have an offset of more like 10V. If its just an offset, I could just account for this in my data analysis, but I'm not sure if there is some sort of drift going on in the long term. I will try some tests in the meantime. Perhaps its some sort of compatibility between the devices issue... Does anyone have some insight on this?

[Tepig]

Hi, I want to check how did you setup wiring.

Did you measure any signal on AI0 or there was no connection? How was AI1?

If there is no connection, the behavior is expected I think.

There is no guarantee that it measures 0.000000......V.

[jane6366]

Hello, thanks for the reply. I had a connection to known signals. I tried a 0 V input and a 4.7 V input. So when the 0V input is attached to AI1 there would be some offset making the signal 0.14V and when the 4.7V signal was attached, 4.84V. For AI0 it reads the correct signals.

[Tepig]

Sorry but I don't have any suggestion... Do you have another DAQ or 2090A?

If you do, why don't you replace the current hardware to that?

[jane6366]

I tried a test which gives me a better idea of which Analog inputs are acting funny. I sent in a square wave with High Voltage +2 V and low voltage 0 V at 100Hz. I checked on the oscilloscope that the square wave was doing what it should (DC coupling, 1 MOhm impedance). I checked that the DAQ device, USB 6366, also has DC coupling. I'm not positive of the impedance, but I think it is quite high.. Then I plugged the same signal into the analog inputs and checked the readings on the computer (plugged into one channel at a time, no other channels receiving a signal), they were as follows: 

AI0 - oscillates between 0Vand 2V (as it should)

AI1 - oscillates between 0.2V and 2.2V

Ai2 - oscillates between 0V and 2V

Ai3 - oscillates between 0.5V and 2.6V

Ai4 - oscillates between 0V and 2V

Ai5 - constant at -10.2V

Ai6 - oscillates between 0V and 2V

Ai7 - oscillates between 0V and 2V

The frequency and shape of the oscillating pulses looked as it should.

So it looks like Ai0,2,4,6 & 7 are behaving okay. But something funny is still happening with the other channels, especially channel Ai5. 

I wonder if its a compatibility issue. It looks like BNC 2090A works best with E and M series DAQ, and USB 6366 is an X series.

Thanks, Kristen