Does scxi-1321 in differential mode require bias resistors?

[ckhassan]

Hello,

I'm using an SCXI-1121 with an SCXI-1321 to excite (3.3VDC) and receive the output of a load cell.

The 1121 is cabled directly to a PCI-MIO-16E-4, and the 1121 channel is set to differential mode.

The 1321 jumper is set to expect a differential signal.

Do I need input bias resistors as shown in the ni field connections document: https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider... ?

Thanks,

Chris   

[NEWKlear]

ckhassan,

The Bias resistors will ensure that there is a path to ground for the signal to be measured on.  While the device will still function without them if the common mode of the signal is higher than that of the SCXI module we may see railing measurements.

[ckhassan]

J Newk,

Thanks for the reply.  So, how is this commonly done with an scxi-1321 mounted on the front of an scxi-1121?  Should I connect the bias resistors from each signal input (signal high and signal low screw terminals) on the 1321 to the ground screw terminal on the 1321?

Thanks,

Chris

[NEWKlear]

Hey Chris,

I didn't see that you were using a load cell in your previous post.  You shouldn't have to worry about the bias resistors in this case and simply hook up EX+ and EX- to the excitation of the load cell and the +/- to the channel plus minus.