GE IC754VSI12CTD Operator Interface Products page 57

Grounding
Shielding
Do not connect Signal Ground (pin #7) to Frame Ground (pin #1) on
the QuickPanel View, except in the specific and limited
circumstances noted in the Grounding section above.
GFK-2306E
A signal return path between transmitting and receiving devices must be
provided. This return path is separate from the Rx and Tx data lines and the
other 422/485 signals supported by the QuickPanel View, and may be
provided by a separate conductor in the cable. Connect both ends of the
signal return conductor to Signal Ground (pin #7). Shielding or use of a
twisted pair for this connection is not necessary.
For installations where all devices are in the same cabinet and have the same
ground potential between devices, connecting Signal Ground between all the
devices on the 422/485 network is adequate to ensure proper voltage levels
at the devices.
However, if there is a difference in ground potential between devices, such as
when the devices are in widely separated cabinets, signal grounds on a
422/485 network should not be tied together. The cable shield and signal
ground should be connected together at only one device, closest to the earth
ground connection.
The signal and frame grounds of the QuickPanel View are capacitively
coupled, but in some devices these ground references are connected
together. Connect Signal Ground (pin #7) to Frame Ground (pin #1) and then
to earth ground on the QuickPanel View only in the circumstance where the
other devices separate their signal and frame grounds and the QuickPanel
View is the only device with frame and signal ground connected to earth
ground.
Shielded cable is required for compliance with CE Mark and FCC
requirements. The cable shield should be connected to the metal connector
shell or by pin 1 of the QuickPanel 25-pin serial connector. Shield and signal
ground (pin 7 of the 25pin connector or pin 5 of the 9-pin serial connector)
should not be connected directly together.
Chapter 4 Detailed Operation
Caution
4
4-15