high noise 9201

[zyl99]

HI,
I'm using a 9201 to measure a voltage signal.
When I wire up the 9201 (ground to a9 and + to a0) i get alot of noise (+- 400 mV) on a 800 mV signal)
I have mesured the signal using another scope and a mulitmeter and get noise values of +- 2mV. (so it's not the signal or the cable)

I tried to rewire the input into a4 to check that it wasn't to do with the channel i was using and the same thing happened.
btw I am not using any other channels in the 9201.
I have also tried several different sampling rates to make sure that wasn't the problem.
I also tried a DC voltage stright from a power supply, and it showed excessive noise if measured using the 9201.
btw I am using the DAQ assistnat in labview to make my readings

Have I wired up the ground incorrectly?
what else could the problem be??
cheers
Zyl99

[TheWay]

Hi Zyl99,

It looks like you may have created a ground loop in your configuration.  Your signal source is most likely a grounded source, and the 9201 only supports referenced single ended (RSE) connections.  For more information on ground loops, refer to this DevZone article (your connection setup probably looks like the 'Not Recommended' configuration in Table 1):

http://zone.ni.com/devzone/cda/tut/p/id/3394

You will need another device (such as the 9215) that can accept differential or non-referenced single ended (NRSE) connections to measure grounded signal sources.

Let me know if you have any other questions.

Regards,

Way S.

NI UK Applications Engineer