PXI 6255 Input Time Constant

[kyh637]

Hello,

I am connecting a somewhat large resistance to the input of a PXI 6255 card, and I'm worried about the time constant at the input possibly being too large. What I'd like to know is what is the input capacitance of the card, or at the least, what is the time constant for my setup? I'm currently using about 200kOhms, and it really couldn't get much lower.  Thanks.

[FmTesla · Accepted solution]

Hi kyh637

NI 6255 Specifications 
https://www.ni.com/docs/en-US/bundle/pci-pxi-usb-6255-specs/page/specs.html

In the specs is mentioned that the impedance between AI+ and AI GND is >100 GOhms in parallel with 100 pF.  So, the input capacitance should be 100 pF.

The reason you might want to know this is to determine settling time, I assume.  If so, there are settling graphs on page 2 of the same specifications document.

Cheers!