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P a n e l M a t e e P r o P S U s e r s G u i d e
RS422 Grounding Recommendations
This balanced interface operates with common mode DC or peak AC voltages
differentials of –7 to +7 volts between grounds at each end of the cable. In cases where
the common mode voltage approaches either extreme, the system may operate properly
when the shield is grounded at only one end of the cable. However, this arrangement
makes the system susceptible to high frequency interference. If the systems do not
operate properly due to high frequency interference and grounding the cable shield at
both ends is ineffective, then total isolation must be considered or ground potentials in
your plant eliminated.
RS422 Shielding Recommendations
Application: Short or Long Runs in LOW or HIGH Noise Environment with
INSIGNIFICANT Levels of Low Frequency Ground Differential Voltage Between
Connected Units
A good quality shielded cable consisting of twisted pairs for the required communication
wires and logic common is recommended. An unshielded line is not recommended
because the unshielded connectors may act as an antenna resulting in radiated
emissions that may exceed the CE specification limit. Additionally, shielded cable
provides greater ESD protection. The shield should be connected directly to the chassis
of the interconnected units at
both ends
. The connector housing should contact the
cable shield uniformly around the entire 360-degree periphery of the housing cable entry
opening. Never connect the shield by way of a drain wire pigtail unless absolutely
necessary. If a pigtail is required, the shield should be terminated as closely as possible
to the connector to minimize the pigtail length.
Application: Short or Long Runs in LOW Noise Environment with HIGH Levels of
Low Frequency Ground Differential Voltage Between Connected Units
A good quality shielded cable consisting of twisted pairs for the required communication
wires and logic common is recommended. The shield should be connected directly to
the chassis of one of the interconnected units (one end only). Never connect the shield
by way of a drain wire pigtail unless absolutely necessary. If a pigtail is required, the
shield should be terminated as closely as possible to the connector to minimize the
pigtail length.
Application: Short or Long Runs in HIGH Noise Environment with HIGH Levels of
Low Frequency Ground Differential Voltage Between Connected Units
A good quality shielded cable consisting of twisted pairs for the required communication
wires and logic common is recommended. The shield should be connected directly to
the chassis of one of the interconnected units and ac-coupled through a 0.01 microfarad
capacitor at the other end to the chassis of the second unit. The connector housing
should contact the cable shield uniformly around the entire 360-degree periphery of the
housing cable entry opening. Attaching the capacitor at the ac-coupled end will require
some ingenuity to achieve a secure connection at both the shield and chassis while
keeping the capacitor lead length as short as possible.
