Well, again I come the the defence of NI. I have used the 6024 board with the 68LP block successfully. However, if you are in a noisy environment, then placing the 68LP in a metallic enclosure, grounding the board common to the enclosure, and running a separate ground braid from the metallic enclosure to a GOOD earth ground will often do wonders. The problem arises from the notebook/power supply combination being often floating off ground. A good indication of this is the fact that most laptop power supplies are switching supplies, and many do not have a 3-wire AC supply plug, hence no gound on either input or output of the supply. In fact, the switching AC power supply can become a source of spurious noise if you are trying to measure very
low level signals, such as the output of strain gauges or thermocouples.
I have had considerable experience removing noise/garbage from pc based DAQ systems, but I still do not consider myself an expert. There have been whole books written on the subject, so please do not take my comments as the be-all and end-all on the subject.
My general rule of thumb is to try and get a good earth ground (not the green wire in an AC line cord) as close to the DAQ board/computer combination as possible, and shield everything else that you can to this point. Also, try not to have more than one ground point in your measurement setup, as this is asking for common-mode ground voltage problems.
Good luck, this is not an easy subject to cover/solve.
Dave
