Elvis II: FGEN, very noisly signal on low level

[fparisi]

We recently purchased some Elvis II platforms: very nice products.

Anyway we have an issue with FGEN when amplitude is very low (about 10~30mVpp) the signal (osserved on the scope) is very noisly.

We use as scope the input AI1 (FGEN <-> input of quadripole which is GROUND referenced) ed AI0 (output of quadripole, always referenced to GROUND)

We connected the two (-) AI pins to common AGND then to GROUND, while FGEN is routed via prototype board.

Does FGEN share the same AI GND?

Where we are mistaking?

Thanks in advance

Message Edited by fparisi on 11-24-2009 06:59 AM

[matteobr]

Hi Parisi,

what do you mean with very noisly? How many mV of noise could you see?

However on Elvis II Specs (http://www.ni.com/pdf/manuals/372590a.pdf) page 7 you'll see that the Absolute Accuracy is 10 bits. So if you have a 10 Vpp as range you may have 10 mV of noise!

Let mw know more infos,

M

[fparisi]

Dear Ing. Brunella, thanks for the reply.

At the moment I haven't with me ELVIS with the circuit, but I remember that AI GND was connected to GROUND together the AI1- and AI0- pins....

I am afraid that the FGEN signal could be affected by a ground-loop noise (is it referenced to GROUND?)...so I guess something is wrong due to a wrong input configuration.

Would be so kind to give me confirm that a reccomended configuration could be like the attached one?

I will check for it as soon as possible.

Thanks in advance.

[matteobr]

Hi Parisi,

have you got a screenshot of your noisy acquisition?

Thanks 

[fparisi]

Ing. Brunella,

on next monday/tuesday I will be in lab and I'll take the screenshots.

Thank you for the support.

[fparisi]

As promised, attached is two screenshots of my SFPs

I simply conencted the FGEN (10mVpp@1kHz sine) to AI 0 input:

FGEN <->AI 0+

GROUND <->AI 0-

Thanks in advance.

[matteobr · Accepted solution]

Hi Parisi,

I think that you do stuff in a correct way. However, it is possible to see some noise (as you see in your screenshot) for a huge number of factor. Moreover, Elvis II is a very useful and powerful device but is not designed for small voltage operation.

Could you see the same behaviour in you acquire a large voltage signal (more than 1Vp)

Let me know

[nykei]

hi

can anyone tell me how can i read digital signals from NI ELVIS board using labview?

in labview DAQ assistant, i can select the line input continuous.

however, is there anything else that needs to be done?

 also, as i am getting those digital signals from ADC0831, is there a way i can make (or simulate) clock signal so that i can

output that signal to Digital Out of elvis and use it to feed to ADC0831 CLK.

i would appreciate any help. thank you