why the noise of my PXI6733 is so large ??

[xiong@wipm]

AOout of my PXI6733 has a very large noise ,about 3.5mv.Offset is about 0.5mv and the rms noise is about  0.8mv.The FET spectroscopy shows that noise from 50Hz, 150Hz,250Hz and so on is very high. Could any one give me some suggestion? thank you very much!

[Liming]

Hi,

The range accuracy of PXI-6733 AO channels is 2.24mV.

And 50, 150, 250...., It seems that there noises come from power supply. So could you connect your PXI system to another power to have a test? 

[xiong@wipm]

my 6733 card is installed in my computer. I find the AGND and the earth are not connet,I test the output using Agilent ocsilloscope directly while the reference ground of  Agilent ocsilloscope is connected with the earth.This time I just changed the power line position of the ocsilloscope,letting the PC and the oscilloscope have the same powersupply,and then the 50Hz noise dissappeared.The noise voltage became to about 2mV with a flat noise spectroscopy,but also with a offset about 1.5mv .I don't know where it comes,maybe the common-mode votlage between the AGND and the earth ??So I have to using the Instrument amplifer AD620, and now the offset is just 0.15mV.

Another problem is about the test panel in the" meaurement & automation "of my labview7.1.I find that when I use the sinewave to test  6733, the offset appears and increases as the update does. But I use my own sinewave VI to test it ,it is ok with no obvious offset.So why??

    thank you for your attention and reply!

[Liming]

Hi xiong,

I don't know why test panel and DAQ VI have different output result. It's strange.

But you could do a self calibration on 6733 for a less offset. 

[xiong@wipm]

hi!

Although I have got a better ouput and very low noise in my system,I can still see some very sharpe lines in my output with amplitude less 10mV.Obviously they are high frequency signial and ruleless,but I can see nothing special from  FFT spectroscopy.If I connect the AGND of 6733 to the earth and then measure the output using Agilent oscilloscope directly, there are no these special lines.

I don't know whether they come form 6733 card or from the environmental noise. Could you give some suggestion? thank you for your attention and reply!