Breakoutbox, Bias resistor/capacity change by using more channels ?

[RaLi]

Hello together !

I'm building a breakout box for my DAQ-Card like the BNC-2110 from NI and have a question that I wanted to clear for me before I finished the box.

The data-sheets of the bnc-2110 says that inside there are bias resistors and a capacity for each analog Channel 5KOhm and a parallel 0,1uF between AISENSE and AIGND.

They are for different modes:

the Floating Source (FS) und Ground Referenced Source (GS)

The RC-Combinations are on every Channel and I found that the
total resitor get down and the capacity get high by using more than one channel.

Is the correct ?

I calculate if I use all 16 Channels in FS-Mode the resistor get down to 312,5 Ohm and the capacity rise up to 1,6uF between AISENSE and AIGND.
Compared the values for only one channel it get from

5K to 312,5 Ohm

and from

0,1uF to 1,6uF.


is this correct and it's normal and everything is allright ?

I found it's a little but strange but ... ?


I hope you can clear my mind.


PS: In the attachment you can see the schematic of it

[Ken_Tobler]

Hello!

The schematic as taken from the BNC-2110 User Manual shows that the signal from the BNC-2110 is connected to the DAQ board in differential mode, in which case the channels are not sharing a common ground.  The resistances and capacitances on each channel would not combine in parallel unless he is connecting many grounded signal sources to the BNC-2110 with the switches set to Floating Source (FS).  If the signal sources are grounded, the switches should be set to GS so that the connection to ground through a resistor and capacitor is opened.

 I hope this information helps!

Best regards,

Ken

[RaLi]

Thank You Ken for Your reply.

You are right.
The schematic shows a differencial application.

The last weeks I had not much time continuing my bulding
and no time to answers you.

Thank again for your help


Best Regards

cubi