Siemens 9700, Installation Instructions Manual, Page: 35 / 45

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RS-485 Connections
The 9700 Power Meter’s communications card includes optical coupling
that provides full isolation between the RS-485 communication lines and the
9700 Power Meter internal circuitry. This circuitry provides protection from
common mode voltages and incorrect connection. All inputs pass the
ANSI/IEEE C37.90-1989 surge withstand and fast transient tests.
Specifications are as follows:
Specification Value (COM 1) Value (COM 2 and COM 3)
Baud Rates 300 to 19, 200 bps 300 to 115, 200 bps
Duplex Half Half
Supported
Protocols SEABus,
GPS:TRUETIME/DATUM,
GPS:ARBITER, Modbus RTU SEABus, Modbus RTU, DNP 3.0, PML
EtherGate, GPS:TRUETIME/DATUM,
GPS:ARBITER
Isolation Optical isolation from all other inputs and outputs (the COM 1 RS-485 port is
not isolated from the COM 1 RS-232 port); isolation voltage is 750 V peak for
10 seconds @ 60 Hz.
Connection
COM 1 RS-485 connections are made via captured-wire terminal strips on
the 9700 Power Meter adjacent to the power supply connections. The
optional X
PRESS
C
ARD
COM 2 and COM 3 RS-485 connections are made on
the top of the unit (refer to the diagram on page 3). Terminal connections
are marked as follows:
Marking Terminal Function
SHLD RS-485 Shield (electrically connected to chassis
ground)
- RS-485 Data Minus
+ RS-485 Data Plus
Up to 32 devices can be connected on a single RS-485 bus. Use a good
quality shielded twisted pair cable recommended for RS-485 application.
The overall length of the RS-485 cable connecting all devices cannot exceed
4000 ft. (1219 m).
General Bus Wiring Considerations
Devices connected on the bus, including the 9700 Power Meter, converter(s)
and other instrumentation, must be wired as follows:
♦
The shield of each segment of the RS-485 cable must be connected to
ground at
one end only .
♦
Isolate cables as much as possible from sources of electrical noise.
♦
Use an intermediate terminal strip to connect each device to the bus.
This allows for easy removal of a device for servicing if necessary.
2
38)
The RS-232 and RS-485
ports at COM 1 are
multiplexed – you cannot
use both ports
simultaneously.
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%98-32
Do not connect ground to
the shield at both ends of
an RS-485 segment. Doing
so allows ground loop
currents to flow in the
shield, inducing noise into
the communications cable.