GS and FS switches on the BNC2120

[jugheadtheegghead]

Hi! I am using BNC cables for analog input into PC. There is a switch which says GS and FS on either sides. I presume its Floating source and Ground source. Can anyone explain to me in what conditions i use which? If its a non-referenced single ended input then which one do i ise? the GS?Thanks!

[Sarah Thompson]

The best place to start is the BNC 2120 User Manual: http://www.ni.com/pdf/manuals/322444b.pdf. On page 6 they start the discussion on floating and grounding signals.

There is also a great online tutorial about floating and grounded signals: Field Wiring and Noise Considerations for Analog Signals:
http://zone.ni.com/devzone/conceptd.nsf/webmain/01F147E156A1BE15862568650057DF15?opendocument.

Hope this helps. Good luck with your application.

[jugheadtheegghead]

Hey thanks i got that sorted out. Another thing is that the BNC manual says that its deafult is differential now i set up my channels as differential too but i get a huge offset. Can u tell me why?
Thanks!

[Sarah Thompson]

Indeed, that is odd. Is the offset present on all channels? Have you done a loop-back test (ie output a DC voltage on an analog output channel and connected that to an analog input channel)?