Noise

[Arthuruuuuuu]

Hey people, thanks for your attention.

I am using the NI 9220 module to measure the voltage around 2 points in my circuit. Unfortunatley, i got a lot of noise. 

Can anyone help me how to deal with the NI 9220 chanels and COM ?

I am conecting positive and negative in holes 0 and 19 and the mesh in COM.

How can i make to have a more precise signal ?

Anyone can help me ? Thanks a lot.

[altenbach]

Noise is irrelevant, it is just the S/N that counts. 😉

Are you measuring very small signals? Is it really random noise or does it have some flavor (50Hz, high frequency, etc.) Do you have any filters matched to the acquisition rate? Do you have a guess for the source of the noise? How is everything connected and terminated?

[wiebe@CARYA]

>I am conecting positive and negative in holes 0 and 19 and the mesh in COM.

The are way more then 19! ways to wire 0-19 holes, and only a few are correct.

A picture of the wiring might help...

And of course the voltage you're measuring could be noisy, but I'd guess you tried a grounded input?

[Bob_Schor]

Find a good electrical engineer who knows about signals and grounding and have her (or him) look at your wiring.  "Noise" (where none is expected) is often a grounding and/or impedance mismatch problem which is difficult to evaluate from a simple text message.  Get someone knowledgable to look at your circuit.  Having an oscilloscope might also be useful.

Bob Schor

[Ben]

CMR is something to consider as well.

Make sure the ground of the DAQ device is coupled to the ground of the DUT. If they are not and exceed the CMR... all bets are off.

As a general reference I highly recommend "Noise Reduction Techniques in Electronic Systems" By Ott. That book has been updated to include computers. He start with Maxwell's equations, establishes some boundry conditions, derives a simplified equation and use then to suggest how to handle every type of noise I can think of off hand.

One rule of thumb he made was rather than try to eliminate noise from a system it is better to prevent it from entering in the first place. Shielding, twisted pair wires,...

Ben