I do data acquisition of sensors which measure velocity of ground motion. I use the acquisition card PXI4472B which work in a pseudodifferential way only.This acquisition card is in the acquisition device NI PXI1042Q. I would like to subtract positive and negative signals of my sensor to reduce the noise. So I put negative signals to the shield because I believe (but I am not sure) that the DAQ will do the subtraction between my positive signal and my negative signal. I believe (but I am not sure) I can do that because the negative signals do not vary more than +-2.5V. But I saw in a documentation that we can't make a non-ground connection to the shield. Some people (where I work) said that it was possible because my negative signal doesn't vary more than +-2.5V. I would like to know if that I did was correct.
The other possibility was to use 2 channels, one for the positive signal and the other one for the negative signal. But don't I loose the dynamic range because I do the subtraction of my 2 signals after digitalisation (with a software)?
An other possibility was to do the subtraction before digitalisation with an ampli-op. But we measure little signals (few mV), so we don't want to do that by our own because we are afraid to make to much noise. Do you make that?
The final possibility was to use an other acquisition card. We have bought also the PXI3060E which is also in the acquisition device NI PXI1042Q. This one work in a differential way, so we don't have all this problems. But this acquisition card don't do vibration treatment, like antialiasing filters.
I have illustrated with 3 outlooks (see the attached file) my first three possibilities. I am open to other possibilities and all ideas will be welcome.
Please help me. Thank you,
ben
Message Edited by benbol on 05-20-2005 06:21 AM
