Input mode for NI-9205

[rich24]

I am building my first datalogging application with cRIO and two sensors.  My question is two-fold.  The first is a wiring question and the second is a question bout COM vs AI SENSE.

First of all, I have two different types of sensors.  The first only has two wires (floating) and the other has three wires (ground referenced).  I would like to wire these in the most intelegent way.  Do I need to take a differential measurement of the ground references sensor?? If so, where should I locate the ground for this sensor.  Likewise, if I am taking a single ended measurement of the floating sensor, what do I ground reference the other sensor.  I hope my question is not too confusing.

Secondly, I would like to take several NRSE measurements of all the sensors, (floating or not) but I am not sure if this is possible.  I have seen wireing diagrams in the operating instructions and specifications document of the 9205.  Am I unsure what the difference is between the COM and AI SENSE modules of the 9205.  Any help here would be greatly appreciated.

[AndyClegg]

Looks like you have seen the operating manual - which is usually a good place to start for typical wiring diagrams. I think if you read this Field Wiring White Paper - that might shed some more light for you. Regarding the AI-SENSE input it makes the following statement which perhaps answers your second question:

"In an NRSE measurement system, all measurements are still made with respect to a single-node Analog Input Sense (AI SENSE), but the potential at this node can vary with respect to the measurement system ground (AI GND)"