Differential measurement using NI 9205 and cRIO ?

[soeren]

Reviewing the different examples in using analog input for th Compact RIO, I am able to make analog input measurements, Single Ended. But I can't seem to get the differential input measurements working. The way I'm acquiring my inputs, is basically the labview example for the cRIO NI 9205 module (the example Basic IO). In this example the settings for the AI channels (RSE,DIFF,NRSE) can be changed, but I still can't get the differentiel part to work. In differential mode the connection is (+ACH0  ,   -ACH8) and I COM is unconnected.

Hope you can help

Regards

Søren

[Morini]

Hi Søren,

One of the most common mistakes made when setting up a differential measurement is failing to establish an input bias current path. For example, a user working with differential inputs may connect a 1.5 V battery to the two inputs of a differential channel and obtain an invalid reading. Adding a resistor of almost any value between either input and the analog common will generally correct the problem.