Grass Valley MOBox Mixed-Operation Systems - Manual (Page 7)

Mixed Operation User’s Guide vii
Triax cable systems
WARNING
Only connect a Triax cable from the same LDK camera family to the unit.
Do not allow system earth currents to exceed 1.5A in the outer shield of the Triax cable
or 0.2A in other cable shields.
To avoid excessive earth currents in a Triax system, galvanically separate the power
earth connection of equipment connected to the camera from the camera earth.
It is strictly prohibited to short circuit the inner and outer shields of a Triax cable used
to connect a camera to a base station.
Galvanic separation
Because of the nature of Triax systems, with long distances between camera and Base
Station, the risk of earth currents flowing is greater. These earth currents can result in
damage to the equipment.
For example, a monitor connected directly to the CVBS output of the camera is
powered locally. The earthing point of the monitor’s power supply can be at a different
potential with respect to the earthing point of the Base Station. If the power earth of
the monitor is also the video earth, then this earth potential is transferred to the
camera via the shield of the BNC connector. The difference in earth potential between
the camera and the Base Station results in an earth current in the Triax system.
• To prevent earth currents from flowing in the Triax system, we recommend
galvanic separation of earthed equipment connected to the camera. This
separation can be achieved by using an isolation transformer between the local
power outlet and the equipment connected to the camera. Alternatively, use
equipment that has a double insulation and therefore does not require an earth
connection.