Siemens S5-135U/155U - Manual (Page 57)

3-31
System Manual
C79000-G8576-C199-06
In these cases, double-shielded coaxial cables (triaxial cables) must be used
to transmit the video signals. The inner braided shield of the coaxial cable
serves as the return conductor and must not be connected to the shield bar.
The outer braided shield provides a path to ground for interference currents
and must be incorporated in the shielding and grounding measures.
To avoid ground loops, the electronics ground and housing ground of the
monitor must be independent. This requirement is met when:
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The electronics and housing grounds of the monitor are metallically
isolated,
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or the electronics and housing grounds are connected via a
voltage-dependent resistor (VDR) fitted by the manufacturer of the
monitor.
3.6.2 Shielding and Grounding
If the monitor and PLC are used under harsh industrial conditions, you must
ensure the following at the PLC end:
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Cables shields should be connected to the shield bar in the cabinet,
immediately after the cable inlet;
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the video cables should be fully stripped;
- the outer braided shield should be secured to the shield bar of the
PLC over as large an area as possible (e.g. with metal ties which
enclose the shield or with cable clamps).
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Shield bars should be connected to the frame or cabinet panel over a large
area.
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Shield bars should be connected to the ground point of the cabinet.
You must ensure the following at the monitor end:
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Separate the electronics ground and housing ground.
-
Remove the jumper at the monitor to separate the two grounds.
- Fit touch protection at the video sockets because hazardous touch
voltages of more than 40 V may be present at the sockets after
separation of the grounds.
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Connect the ground clamp of the monitor to the protective conductor.
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Connect the cable shields to the ground clamp of the monitor;
-
fully strip the video cables;
- secure the outer braided shield to the ground clamp of the
monitor over a large area.
Installation Guidelines