BNC-2090 bias resistors in Diff mode w/ PCI-6284

[nislyj]

Hello, all

I have an NI-6284 with two BNC-2090's which I am using in 16 channel differential mode.  I have installed 100K bias resistors in the "B" position per the 2090 manual on page 2-11, but have not installed the bias resistors in the "A" position as it seems that it  isn't necessary if the inputs ar DC-coupled, if I understand correctly.

The problem I am trying to troubleshoot is this:  if I apply a 5V potential across any input, every input of the card registers as 5V, +/- a few hundred millivolts.  if I apply a dead short across the adjacent channel, that channel goes to zero, but all of the others hover around 200-300mV.

Will installing the second bias resistor in position "A" take care of this?  Any idea what is causing this?  I'm not sure I understand why the entire board lights up when I apply in input to one channel.\

Thanks.

James Nisly

[Hal_L]

Hi James,

Reading open channels will always yield unpredictable results. So, the behavior that you are seeing is not totally unexpected. However, connecting another bias resistor in the "A" position should fix the problem.

Regards,

Hal L.