Multiple signals to the same common ground?

[istvanb]

Hi,

I have to measure 4 different floating signal in a noisy environment. Cables are quite long (1-2m) and what I have experienced is that my signals are getting quite noisy. The instrument though has a common ground terminal on its enclosure (wires can be connected with a screw). Can I use shielded cables for the signals and connect the shield to this terminal? What are the implications?

thanks in advance!

 

[GreenGiant]

using a shielded wire in this manner should work, BUT first I would say try checking to make sure that the common ground is a true earth ground, this will ensure that it is grounding properly, then try generic shielding.

If you are still having issues then you may have to make duplicate data cables and do some noise cancelling.

 

[Harald Kapp]

Hard to say without knowing more about the nature of your signals.

As long as the shield is isolated from the signals, you should be able to tie it to a common ground. Apart from some exceptions it is even advisable to tie both ends of the shield to ground. This allows any disturbance to flow equally to both ends of the cable thus minimizing electromagnetic interference into the inner wires. Keep the connection from shiled to the terminal as short as possible and minimize the length of the unshielded ends of the cables.

 

[istvanb]

Thanks a lot for both of you.

About the signal: I try to do some measurements on massive DC motor. I assume that itself adds noise, but anyways other different noisy stuff is going on in the same room.

I will connect the chassies ground to earth first (actually I am wondering now why I have left this step) and check the difference. If the results are the same or not good enough I will move forward and use shielded cables.

Your help is really apprechiated!