50Hz AC noise

[caoyuqi]

I am using several coaxial cables with single BNC connectors to route signals to the AI pins of a PXIe-6358 card via a breakout board. ​​The signals are configured for differential input.​​ I am encountering a significant 50Hz noise issue when the BNC ends of all 8 coaxial cables are left floating (unconnected).

To troubleshoot, I disconnected the cables two at a time. ​​The 50Hz noise on the corresponding channels disappeared as each pair was removed, and the issue was completely resolved only after all cables were disconnected.​​ I am unsure what is causing this problem and would appreciate any insight.

Please note that I am currently unable to attach any diagrams or screenshots.​

[santo_13]

If only one end of the BNC coax cable is connected, then it is acting like antenna and picking up mains 50Hz interference, once the BNC shield is properly grounded it will be minimized.

Why is this a cause for concern when you don't have anything connected to the cable?

Please read this article - Field Wiring and Noise Considerations for Analog Signals - NI