NI-USB-6001 measure nosie level

[hasse]

I am using a NI-USB-6001 to measure some voltages @ 5V level.

I am trying to use one input to measure the noise level on top of a 5V signal. The ripple is roughly 200mV p-p (when looking at a scope in AC coupling mode). I can't find a suitable setting in the DAQmx VI to set it to measure with a higher resolution (4.9V-5.1V)

to be able to see this ripple.

[rpursley8 · Accepted solution]

You might try setting up the AI line as a differential input (AI0/AI4).  Feed your signal input AI0 and ground your signal to a DGND.  Then feed the +5V on the USB-6001 to AI4.

[SunshineDesign]

A better method might be to DC decouple the noise by using a DC Block capacitor with good RF response from near DC to some freq desired. With just the AC component on the line, you can go to much better resolution than you can at the range setting for 5VDC.

[rpursley8]

Depends on what the noise is.  It might at least partially get filtered out with the addition of the capacitor.

[SunshineDesign]

That is true depending on the value and type of capaciter is selected. Higher c value leads to lower reactance at lower frequency. Lower freq cutoff being the bigger problem. Sometimes high and low value are sued together to get pass at low and high freqs like with bypass caps on digital chips. None the less, it works and works well. 

[rpursley8]

It really depends on the purpose of the exercise.  Since analysis seems to the be goal, I don't think you would want to change it by filtering at all.