Electrical, magnetic and electromagnetic interference fields are
weakened by means of shielding
Via the shielding rail, which is connected with low impedance to the
rack, interference currents are shorted by the cable shield to the
ground. It's important that the connection to the protected ground
conductor is impedance-low, because otherwise the interference
currents may cause interference.
For the use of shielded cables the following rules are important:
n The screen cover should be higher than 80%
n The cables have a copper braid (shield / screen)
n Normally the cable shield must be connected to ground in both
sides of the cable. Double-sided grounding is necessary to
achieve high-quality interference suppression in the higher fre-
quency range. The cable shield can be connected to single-
sided grounding in exceptional cases, but if that is done, only
lower frequencies will be absorped.
A single-sided ground connection of the cable shield may be
convenient, if:
– the conduction of a potential compensating line is not pos-
sible
– analog signals (some mV respectively μA) are transferred
– foil screens (static screens) are used instead of screens
made of copper braid.
n When using data lines always use metallic or metallized plugs
for serial couplings. Fix the cable screen of the data line at the
plug rack.
n It is convenient to strip the insulated cable interruption free and
lay it on the isolation/protected ground conductor line (sta-
tionary operation).
n Metal cable clamps to fix the cable shield have to be used. The
clamps must clasp the copper braid extensively and have good
contact.
n The cable shield has to be laid on a protective earth rail directly
after the entry of the cable in the cabinet. Do not attach the
cable shield again on the CNC control / PAMIO device.
CAUTION!
Please observe at installation!
At potential differences between the grounding points,
there may be a compensation current via the cable
shield grounded at both sides.
Shielding Of Conductors
PA 8000 EL CNC control unit
Technical data
24.09.2015 | 71
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