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Bad readings with a group of floating and grounded diferential signals with 9205

 

I have 3 AC grounded signals (60Hz 0-5V) in differential configuration in Chanels AI0-AI8, AI2-AI10, AI4-AI12 with ground to AISENSE and to COM as recommended in user manual for 9205.  These 3 signals share the same ground reference.

and 3 AC floating signals (60Hz 0-5V) in differential configuration in Chanels AI1-AI9, AI3-AI11, AI5-AI13, with 22k bias resistors for every line to COM.

 

All readings for the floating signals get saturated.

 

But If I change the connection order as follows I get apparently good readings:

the 3 floating signals in Chanels AI0-AI8, AI2-AI10, AI4-AI12

and the 3 grounded signals in Chanels AI1-AI9, AI3-AI11, AI5-AI13

 

It seems that Channels AI0-AI8 should always have a floating signal connected.  Why?

How does the modul 9205 manage these connections and ground references?  Or what I am doing wrong.

 

Many Thank in advance

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Duplicated Post:

http://forums.ni.com/t5/Discusiones-sobre-Productos-NI/Comportamiento-extra%C3%B1o-con-el-m%C3%B3dul...

Ricardo Ramos
Account Manager
+5511989658513 | ni.com



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