Re : How to connect AIGND in case of multi differential measure with PXI6221

[benc13]

Hi,

I need to make 8 differential measures with the PXI6221 of floating source. Some has low impedance and some has high impedance.

On the figure below I understand that inputs are multiplexed but it is the same for AIGND ?

Can I plug them as follow for 2 differential measures of source0=(S0+, S0-) and source1=(S1+, S1-) :

Floating source terminal     |     chanel name     |     pin number

___________________________________________________

S0+                                                 AI0                          68

S0-                                                 AI8                           34

S0-                                                 AIGND                     67

S1+                                                AI1                           33

S1-                                                 AI9                           66

S1-                                                AIGND                      32

Will S0- and S1- not be in short ?

Thanks,

Benoît Chantepie

[Jean-Luc_D.]

Hi,

All Ai GND are connected together.

You can plug for 2 differentials measures as you did.

There will be no short circuit between S0- and S1-, both pins can be at the same location (understand same potential), there is no problem with that.

Regards

[benc13]

Ok thanks,

So whatever the internal impedance of my floating source, I have to add a resistor between all AI- and AIGND to don't modify the behavior of my circuit.

Benoît Chantepie

[Jean-Luc_D.]

This is not a mandatory, if the impedance you measure is very low (<100 ohm) no resistor are required.

http://www.ni.com/pdf/manuals/371022k.pdf (pages 4-15)

Actually we add these bias resistors to avoid the source to float out of the maximum working voltage range, so to be sure the circuit works.