Screening is one method commonly used to reduce (attenuate) the
interference pick-up from magnetic, electrical or electromagnetic
fields.
n
Interference on screens is conducted to ground by the conductive
connection between the screen and the screening rain/enclosure.
To avoid interference from these currents it is very important that
the neutral connection is a low-impedance connection.
n
You should only use cables that are provided with a braided
screen. The degree of screening should be more than 80%.
n
Avoid cables with foil-type screens as the foil can be easily dam-
aged by tension and pressure at the point of attachment; this can
result in reduced effectiveness of the screening action.
n
As a rule you should always ground the screens of cables on both
ends. This is the only way in which you can ensure that high fre-
quency interference is attenuated properly.
In exceptional cases it may be necessary to ground the screen on
one side only. However, this will only attenuate the lowest frequen-
cies. The one-sided grounding of screens may provide advantages
when:
n
It is not possible to install an equipotential bonding conductor
n
Analogue signals (a few mV or mA) must be transmitted
n
Foil-type screening (static screening) is employed.
You should always use metallic or metallised covers for serial data
lines. Connect the screen of the data line to the cover. Do
not
con-
nect the screen to PIN 1 of the connector! In case of stationary opera-
tions it is recommended that the remove the insulation from the
screened cable without cutting the screen and to attach this point to
the screening/neutral rail.
Potential differences can give rise to an equalization
current via the screen connected between the two
ground connections. In this case you must install an
additional equipotential bonding conductor.
Please observe the following points when you handle the screens:
n
Use only metallic cable clamps when connecting the screening of
cables. These clamps must provide a good electrical contact and
a large-surface connection to the screen.
n
Attach the screens to the screening rail directly at the point where
the cables enter the enclosure. The screening conductor must be
continued to the module without interruption, however, it must not
be connected to the module!
Screening of lines and
cables
One-sided grounding of
screens
Connecting the screen
VIPA HMI
Installation guidelines
EMC-equitable cabling
HB160 | PPC | 67P-PNL0 | GB | 16-42
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