Fist of all, if you tell us what type of board you are using we may have better help for you.
Adding capacitors should be a last resort, because they can have a drastic impact on the signal, or even cause errors in the readings. I would strongly suggest reading NI Application Note 025, it will help. <>
1. Check your grounds, a bad ground can cause noise, and even create ground loops. If you have more than 1 connector box, ground them to each other.
2. Look into using shielded wire. Even a piece of aluminum foil wrapped around your wires and grounded to your DAQ system can have a big impact.
3. Try to route your wire away from other electrical devices like motors, lights,
and computers. I have seen longer harnesses routed away from elecrtically noisy stuff work better than short ones.
If you are really set on using capacitors, try putting them insde your DAQ connector box, just to help minimize capacitive loading and protect them. Try to keep their leads as short as possible. Put 1 lead on the input signal, and the other end tied to a good ground in the connector.
