Common low in Differential Mode: Urgent

[navneet]

Hell forum,

I have a situation where I cannot use RSE connections due to noise considerations. So using my USB 6212 I have attached 8 of my sensors in differentiaL mode with the return line common to all 8 AI(-) inputs and is a reference sensor. i am using 100 kohm bias resistor on all AI(+) lines as well on ALL AI(-) lines. Is this correct? I mean since the AI(-) lines are common to all, should I be connecting only one 100 kOhm? 

I am thinking since I have connected 8 bias resistors on a common line shared amongst all AI(-), this effectively reduces the bias resistor to much lesse value (parrallel connection).

Please advice 🙂

cheers,

[Danny_Funk]

navneet,

Yes your set up is correct, you need bias resistors on all lines. The following document covers this well.

Field Wiring and Noise Considerations for Analog Signals

Regards,

Danny F

[navneet]

Thanks Danny for your reply. ut it still buggers me if I connect all 8 bias. Since at any given time when any of  the switch is connected, it will "feel" 8 bias resistors connected since this one line gioes to each of the 8 AI(-) inputs! I think this will be redundant and can be accomplished with only one bias resistor? Please see attahced file for scheme.

[Danny_Funk · Accepted solution]

navneet,

If the AI- lines are all connected to the same node on your measurments, then yes you can use only one bias resistor.

Regards,

Danny F