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4 SIGNAL GROUNDING
To effectively ground a shield of a wire or cable carrying
signals, the shield must be intentionally connected to earth, or
to some conducting body serving in place of earth, through a
low impedance ground connection.
Wire or cable shields must be grounded at one end only to
eliminate circulating currents and resultant noise by
eliminating differences in potential between the two ends.
Shield drain wires must be as short as possible and insulated
from each other and other conducting objects, except at the
point of connection. When connecting a shielded, twisted-pair
input to the C1900 terminal block, see Figure 4.1, ensure that
the extension of the shield from the cable jacket is as short as
possible – (preferably 25mm / 1.0in or less), and maintain the
twisted-pair configuration of the two wires up to the point of
termination.
Fig. 4.1 C1900 Terminal Block
If a double-shielded wire is used, ground the inner shield at
one end and ground the outer shield at the other end.
Note. Thermocouples should always have their
shields grounded at the process end only, to avoid
charging currents.
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