Hi John,
I understand that you'd like to eliminate as much noise as possible from your 6036E analog input signals. The 6036E does not have any onboard filtering, so adding filters for each channel as you have done will help increase the signal to noise ratio. I assume that you have added the filters close to the signal sources as that is where they are most effective. Unless the cable connecting the signals from the I/O box to the 6036E is extremely long, or the cable resides in a highly noisy environment, I don't think adding filters between the cable and the card will eliminate much noise. Since the cable is shielded, noise will not significantly mar the signal between the I/O box and the 6036E.
While I do not recommend adding filters between the cable and the 603
6E, adding them should not compromise signal integrity, so trying shouldn't hurt. On the other hand, trying a higher order filter or possibly a bandpass filter might eliminate more noise from your system. You did not mention how you added the filters to the system, but if you are not using a National Instruments signal conditioning accessory (SCC or SXCI), you may want to investigate using one since they are most compatible with NI Data Acquisition devices.
Thanks for contacting NI,
Marcus G.
