Signal noise in current measurement (NI 9203)

[rmichels]

Hello,

I am getting a very high amount of noise in my output signals from my NI 9203 module.  The noise seems to amplify when I turn the fans on in our facility (exhaust fans for fire research) and I need to find a way to stop this.  One theory I have is that I need to use a differential input instead of having all the negatives enter a common.  Is this likely to help?   In this case, can I use the 9203 as a differential input for 4 of my signals and then buy another one, or is there a better device for the job?  I have 4 signals coming in from pressure transducers, 3 from a gas analyzer and one from a propane flow meter.   I am also using a 25' USB cable.  Could that also be part of the problem?

I'm kind of new to this and really appreciate any help.  I can provide more information if needed.

Thanks,

Richard

Carleton University.

[Corby_B]

Hello Richard!

Thanks for your post. So the 9203 can only be used in a Single Ended mode (Ground Referenced). This means that you cannot use differential on this particular board. There is a card that I would recommend which is the 9205.  It has 32 SE or 16 Differential inputs and this could easily cover your application if read you correctly. 

Some possibilities to reduce the noise you are seeing is to use twisted pair shielded cabling to your sensors. If you are not using twisted pair it can pick up noise on the lines. How far away are your sensors from your 9203? Also the USB cable should be OK but you are really close to the max length before you need to actively boost the signal. Do you have a shorter one that you could try just to make sure we rule that out? Let me know if any of this information helps you and I wish you the best!

Field Wiring and Noise Considerations for Analog Signals

Cheers!

Corby_B

Message Edited by Corby_B on 12-02-2008 03:55 PM

[rmichels]

We actually have a 9205 that we switched some of our signals to today and that seems to be helping.  I also started switching to shielded cable and will finish tomorrow.  Hopefully this cuts the noise down to an acceptable level.  I am wondering whether it would be a good idea to use the shielding as the negative wire because the module doesn't have a shield input.  Is there a better way?  The unit is quite far from the sensors (maybe 10-15 meters) and we have very large fans.  I'm hoping to test out everything tomorrow.   Thanks for your reply.

Richard