I have a controller board powered by DC that may or may not be isolated from earth ground. The chassis of the device is non-metallic. This board connects through a long (30-40m), shielded cable to a small sensor board. The sensor board does not electrically connect to anything else, and is also housed in a non-metallic enclosure.
I know the usual "best practice" recommendation is to connect the cable shield to ground at only one end, and this recommendation makes sense when that grounding would be to a conductive, earthed chassis. Any noise induced on the shield would be shorted to earth and be kept away from my sensitive circuits.
However, in my case there is no conductive chassis, no separate earth wire connection to the system, and even the ground return of the DC input to the system may be earth-grounded or it may be battery powered (and thus completely isolated from earth). Does it still make sense to connect the shield to the ground of my circuit in this case? that would mean connecting it to the signal-ground layer (as there is nothing else)... I worry that any noise induced on the shield would just couple more effectively to my circuit through the suggested connection to ground. I'm essentially connecting a huge antenna to my circuit...
On the other hand, I heard everywhere that a completely unconnected shield is as bad or even worse than no shield at all.
So, what would be a good grounding scheme in such a situation?