which of single ended referenced & non-referenced is better in cutting crosstalk

[shantaram]

I am using a SCB100 box to go into PCI-6031E(DAQ CARD) to go into a windows 2000 pro PC. I am running 2 speakers one at 98HZ and other at 112HZ and trying to measure distortion of my acoustic sensors. I know that differential mode in SCB100 box causes no cross talk between the channels. But I want to run a B&K 4190 microphone in single-ended mode only. B&K has just way too high noise floor and lot of harmonics when I run it in diff mode. SO, I would like to know from you guys
if single ended referenced mode is better or the single ended non-referenced mode in terms of cutting cross talk between channels.

[Filipe A.]

Hello;

Differential Mode is always the best mode to use. Make sure you inserted a BIAS resistor in between the ch- and AIGND to create a path to ground for the signal. That might be the reason for the noise you are seeing there.

Regarding your question, RSE and NRSE are alike. The main difference is, if your signal source is referenced to GND, you can create a ground loop and damage the DAQ device, if you use RSE.

NRSE, pretty much will adopt a reference, that is not ground, to reference all the signals. So if your signal sources are offseted from each other, you might see an offset on your readings.

Again, the best method is Differential Mode. I suggest you to double check the placement of a BIAS resistor on it. 100K ohms is a safe choice.

Hope this hel
ps.
Filipe A.
Applications Engineer
National Instruments

[shantaram]

Hi Filipe,

Thanks a lot for the suggestion. How do I choose a number on BIAS resistor? Does that depend on the type of sensor(i.e., thermocouple or a microphone) I am using in diff mode? Do you have any practical value in your mind that you can suggest for a thermocouple.

[<Mike Ross> mross@smpcorp.com]

shantaram,

The bias resistor allows the input to the DAQ card to function properly. Without it the card may accumulate charges that distort the incomming information. The bias resistor provides a way for these charges to dissipate. The 100kohm resistor provides a path for these charges without influencing the signal of interest.

Try this link for some refences:

http://search.ni.com/query.html?tx0=Differential+bias+resistor&op0=%2B&fl0=&ty0=w&tx1=&op1=&fl1=&ty1=w&tx2=&op2=%2B&fl2=&ty2=p&tx3=&op3=-&fl3=&ty3=w&advquery=on&lk=1&nh=10&ht=0&qp=+contenttype%3ATutorial+subsection2%3AdzTechPres+subsection2%3AdzTutorial&qt=&qs=&col=alldocs&qc=&pw=575&la=en&qm=0&st=1&oq=&rq=0&layout=TechResources&ql=a&si=0

Or Search the Technica
l Resources for: Differential+bias+resistor
(limit the search to tutorials and application notes

at:
http://search.ni.com/?col=alldocs&layout=TechResources&ql=a

This is a good article:

Field Wiring and Noise Considerations for Analog Signals found in the tech resources.

Mike