Hi tyro
Sounds like ground loop noise, to me.
If you are using a DAQ card that can do differential measurements, use it.
Don't rely on the ground as a return path it is usually full of rubbish.
Run the two wires as twisted pair right up to the point of measurement and
then ground the negative wire. This should bypass the ground noise.
If this is not possible, try isolating the signal grounds from the shield
and power grounds and common them at only at the measurement point.
If you have done all of the above and the DC offset is still their, then
try connecting the differential wires together to ground (without the
sensor!) if you still see a DC offset then it is coming from the DAQ card,
it may require calibrating.
If you can do this stuff then you
won't probably need your digital filters
to remove the 50Hz either...
There is some good stuff on this on the NI website and in the DAQ card
manuals.
I hope this help
Tim
tyro wrote:
> hi!I was borthered with 50hz and 0hz interference when i use DAQ.I can
> get rid of 50hz interference by using digtal filter,but can not kill
> 0hz because the singal that I want is DC,how can i do?
> thanks for any help!
