Measuring DC on AI - Reading fluctuates randomly

[Daryl]

I have an SBRIO wiith which I'm attempting to measure a DC voltage on an ai channel (single ended). An indicator on the vi bounces all over, yet a DMM attached to the same ai channel displays a voltage (2.503V in this case) solid as a rock. I believe I have followed good practices with regard to ground loops and proper RSE configuration per NI white papers. Is there a low pass filter, averaging vi or other signal conditioning technique I need to be using to realize a solid voltage display? Would this be caused by wait time in the loop or improper sample rate (set at 8usec default)? Thanks in advance.

[PackersFan]

Almost any NI DAQ hardware (C Series cards and sbRIO included) are going to be VASTLY more precise than your multimeter.

This means that you're going to read almost ANY and ALL fluctuation of the signal.  While your multimeter may be showing 2.503 V, your sbRIO is probably reading 2.503124576, and then 2.503776534, and then 2.503788211, and then . . .

So that value appears to jump around, but really it's just a more accurate representation of the signal which - in reality - is jumping around quite a bit.

Before you start worrying about filters, the first thing I would do is limit your front panel indicator to a precision of 3 decimal places and see what you get.  My guess is that your measurement is going to be pretty steady.  In fact you can probably use 5 or 6 digits of precision and still have a very stead signal.