How should the cable shield be grounded?
When using coaxial cables, the shield carries common and therefore, is grounded at the monitoring system. The shield must be isolated from the sensor housing to prevent ground loops. When using two conductor shielded cable, two methods are available. a. If the sensor housing, is electrically connected to the machine (i.e., stud mount), the cable shield is typically connected to the sensor housing and thereby tied to machine ground. In this type of installation, the shield should not be tied to the monitoring system or ground loops may develop between the monitor ground and the machine ground. b. If the sensor housing is electrically isolated from the machine (i.e., many cement mounting installations), then the shield should be tied to monitor ground. It is recommended that the shield be isolated from the sensor housing in this type of installation to prevent ground loops in the event that the isolation between the sensor housing and the machine is lost.
