Analog Input on the 6225

[Steve at INI]

Hi,

I am a little new to DAQ so please pardon the possibly naive question.

I want to use the 6225 card's 40 DF Analog inputs to measure 40 different voltages simultaneously. Each voltage is a cell in a fuel cell stack so the anode of one voltage is the cathode of the next etc up the stack. Will wiring each DF pair anode to the next cathode affect the operation of the card at all?

Thanks

Steve

[gwd]

These are differential inputs but the common mode signal must remain within allowable limits. if i understand the specs correctly, this means BOTH inputs must lie between +/- 10 V IF you set the card to the 10 V range. Now if you have 40 cells in series, and each produces 1 V, that means that even if you ground the cell at the middle some inputs will see common mode voltages as high as 20 V. So unless the voltages are a lot lower you can't do this for 40 cells in series.

Now if the cell voltage is lower (say 0.5 V) in principle you can measure all the cells. However the ones with the largest common mode will incur some error. This may or may not be significant depending on how accurate you need to be.