janitza UMG 801, Руководство пользователя, Страница: 50 / 106

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9.3.1 Shielding
For connections via the interfaces, use a twisted
and shielded cable and observe the following for
the shielding:
·Ground the shields of all cables leading into the
switchboard cabinet at the cabinet entrance.
·Route the cables into the switchboard cabinet
through suitable cable inlets, e.g. PG glands.
·Connect the shield to a noiseless ground
and ensure a large surface area with good
conductivity.
·Do NOT connect the shield to terminal C (GND).
·Mechanically restrain the cables before the
grounding clamp to prevent damage from cable
movement (strain relief).
Fig. Shielding design at entrance to switchboard cabinet.
Cable
Strain relief
Braided shielding
of the cable
Grounding clamp
Noiseless ground
Switchboard cabinet inlet,
e.g. via PG cable glands
WARNING
Risk of injury due to high currents and high
electrical voltages!
Atmospheric discharge can cause transmission
errors and dangerous voltages on the device.
Therefore please abide by the following:
· Connect the cable shielding to functional
earth (PE) at least once.
· For larger sources of interference or
frequency converters in the switchboard
cabinet, connect the shielding to functional
earth (PE) as close to the device as possible.
· Comply with the maximum cable length
of 1,200 m (1,312.34 yd) at a baud rate of
38.4 kbps.
· Use shielded cables.
· Route interface cables spatially separated
or additionally insulated from mains voltage-
carrying system components.
9.3.2 Termination resistors/Termination
The device contains an integrated termination
resistor (S1). Terminate the beginning and the end
of your bus segments with termination resistors
(switch S1 of the UMG 801 = "I" or with termina-
tion resistor 120 Ω/0.25 W - see chapter„9.3.3 Bus
structure (bus segment)“ on page 51).
Right
Wrong
Terminal strip (switchboard cabinet).
Device with RS-485 interface
(Without termination resistor).
Device with RS-485 interface
(Termination resistor on the device).