PCI-6224 Fully Differential Analog input problems.

[royyytheduck]

I'm using the PCI 6224 I/O board and I'm having problems with the fully differential analog inputs. I have the pins connected to a power supply in order to test their functionality. When testing negative voltages it works perfectly. While testing the positive voltages when the test voltage is above approximately 5V the results it gives out jumps from the actual voltage to about 10V repeatedly. On a plot it looks like a square wave. Does anyone know what would cause this?

[taper · Accepted solution]

Do you have biasing resistors on the +/- lines?  Sounds like you're floating out of the common mode range.  Check out the field wiring guide.  https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider...

[royyytheduck]

I'm using the SCB-68 connector block and it looks like it already has biasing resistors on it. The range of the inputs is supposed to be +10/-10.

[taper]

Biasing resistors would go on pads B and D.  All others should be empty unless you have other conditioning.  What value resistors do you have, and what locations?