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How to assign input of DAQ card with respect GND

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Hi to all ,,,

when I connect the two ends of the wire as follows:


 1) one end of the wire pairs connected to the +ve , -ive in the DC power supply 
2) another end of the wire pairs connected to the +ve, -ive in the A10 channel of DAQ 6009
3) when i connected DAQ 6009 USB to the PC , It reads the exact DC voltage as shown by the DC power supply values
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4) Suppose if i connect one end of the wire pairs connected to the +ve , GND in the DC power supply 
5) another end of the wire pairs connected to the +ve, GND in the A10 channel of DAQ 6009
6) when i connected DAQ 6009 USB to the PC , It will not reads the exact DC voltage as shown by the DC power supply
 
 
Please provide a solution to capture the analog signals when the connection was +ve and GND using DAQ6009.
 
We also tried the different terminal configurations like i)differential and ii)RSE but it wont read exactly the values of the DC power supply values
-- 
Warm Regards, 
Ganesan
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Solution
Accepted by topic author erganesh

I recommend reading zone.ni.com/devzone/cda/tut/p/id/3344 but I would also like to know more about your power supply.  Is this a bipolar power supply like +/-15V and GND is in the middle?  How about telling us the model number and where to get a manual for it?

 

Albert

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Hello CPUT, 

 

It sounds like you are experiencing the effects of ground loop losses.  This happens when connecting a grounded signal source with a reference signal-ended configuration.  Please see table one of the field wiring and noise considerations for analog signals for more information on how to successfully wire your system.  This can be found in the link albertm posted (http://www.ni.com/white-paper/3344/en#toc3)

 

Patrick W.
Applications Engineer
National Instruments
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