wring of NI 9205

[Qingqing_Liu]

Thanks. My system is simple. A sensor can output 0-10 V signal, and I want to capture it to NI 9205.

We are seeing the same diagram. Yes, there is a Vcm. I think Vcm is noise voltage instead of a physical device. (Maybe I am incorrect). If you see V2, and its negative is directly connected to AI9, COM, and chassis ground.

I want to connect my sensor only to Al0 and Al8, and leave other channels open, including COM. But I am sure whether this way can make the measurement inaccurate. 

[nanocyte]

Some sensors (floating) have two outputs — a + output and a - output. Vcm is not noise exactly. Vcm is common mode voltage—you have to make sure doesn't exceed the spec of 10.4V.

But, it sounds like maybe your sensor has just a + output. If so, that's a single ended source and that's part of what's confusing here of how to wire it. You might consider using the NRSE Voltage Signals wiring diagram

[Qingqing_Liu]

Thanks so much! I checked my sensor, it has a positive and a reference ground. Do you think my sensor should be wired using NRSE? Instead of Grounded Differential Signals?

[nanocyte]

Your sensor has effectively 3 terminals? Power in, ground, and voltage out? Then, yes, NRSE would be the first thing I tried. I expect it to perform very well. If for some reason it doesn't, the next thing I'd try is  Floating Differential Signals