Suggestion required to minimize the Noise in a DAQ system if clear earth is not available.

[aamir055]

Dear Everyone,

Please suggest what to do to minimize the nose of a DAQ system if the clear earth pit point is not available.

[James_McN]

Hi Aamir,

Without an earth to shield the noise then you need to try and identify the source and try to avoid the noise coupling to sensors and cables.

If there is a serious noise issue I will capture some data and FFT it so I can see what frequencies are at play. 50/60Hz is likely to be from power - 4kHZ from motor drives. Try turning culprits on and off like lights, motors etc and see if it changes.

Once you have an idea of the cause then you can look at reduction. I'm assuming from your comment about ground you are saying to you can't shield to earth ground but you should be able to use the ground side of the power supply to your system. Other things I have seen help:

* Check signal grounds are correctly connected and the DAQ card is in the right wiring configuration

* Try running cables in different paths. Avoid running near power cables and cross them at 90 degrees if you must

* Avoid very cheap DC power supplies.

* Use twisted pair cables in differential mode

Obviously this is just general advice, if you can explain your setup more there may be more specific things.