BNC2115 wiring - Differential connection

[CHgeorgeCH]

I am using a PXI-6071E card to measure ~30 Analog inputs (Floating source signals) in Differential connection configuration. I will use a BNC-2090A (first 8 signals) and a BNC-2115 Extended IO (rest signals) connector blocks. Interconnection between the DAQ card and the two connector blocks is made with a SH1006868 cable.

I am looking for your advice concerning the hardware installation:

According to NI application notes, when applying Differential configuration I should connect bias resistors (10-100 kOhm) between the “+” and ground and the “–“ and ground for every signal. For the BNC2090A this is possible with soldering those resistors on the specific places that exist on the board.

For the BNC2115, according to manual, the only thing that needs to be done is to turn the respective dip-switch of every channel to the FS (Floating Source) position. However, this wiring configuration does not fully comply with the Application note, because this deep switch connects only the “-“ of the signal and the ground, using a resistor/capacitor in between.

My question:

Should I simply rely on this (which means that the 8 signals will have different connection to the DAQ compared to the rest)? OR

Should I disregard the dip-switch on the BNC2115 (i.e. leave it in the GS position that disables the above described connection) and apply the bias resistors on both “+” and “-“ (most likely making the implementation outside the connector block)? OR

Any other idea/suggestion would be welcome.

[Dani87]

Hi CHgergeCH,

what are your concerns if the "8 signals will have different connection to the DAQ compared to the rest"? 

Regards.

[CHgeorgeCH]

Hi Daniel,

I would say it is mostly technical concern, as I have to understand what I do and not just connect to a black box. If, for any reason, I need to troubleshoot this at a later time, I should have some standing point.

Apart from that, this system will be handed over to a client and he may also, from his side, raise similar questions.

Regards,

G.

[Dani87]

Hi George,

as I see it there is no difference in the differential connection from the BNC-2114 to the BNC-2090A. The only difference is that the BNC-2114 is using a RC-element to achieve the equipotential bonding and the BNC-2090A is doing that using the mentioned resistor. I think it is okay to use the recommended FS switch.

If you need more info your question has to be more specific.

Best Regards.

Daniel