GE Industrial Solutions POWER LEADER PMCS Network Architecture Guide - Manual (Page 20)

Power Management Control System
Chapter 2 – Network Design
10
2–1 Modbus Rules
The most basic network configuration for PMCS assumes
that the software is running on a host PC supporting one
or more RS-485 networks on the Modbus protocol. (See
Figure 1 for an example of this configuration.) Table 2 explains the configuration rules for PMCS
networks based on the Modbus platform. Commnet IEDs
may be integrated through the Modbus Concentrator (see
Table 4 for commnet wiring rules).
Host PC is
based on: Follow these rules for the
host…
And these rules for the attached Modbus network(s)…
Modbus 1. The host PC can support
up to 256 independent
Modbus networks. The
actual number is
determined by the
communication cards
installed in the host PC
(see below).
2. The Modbus networks are
connected to the host PC
via an eight-port RS-485
communications card.
3
An option for more
limited systems is an RS-
232/RS-485 converter,
which permits a single RS-
485 network.
4
3. The host PC must be
located at one end of the
Modbus network(s).
1. Each Modbus network supports up to 31 physical Modbus IEDs
and up to 247 Modbus addresses. This is possible because
commnet IEDs attached to Modbus Concentrators occupy
Modbus addresses but do not create an electrical drain on the RS-
485 network and thus are not counted as physical Modbus IEDs.
2. Each Modbus network must be properly terminated at each end
of the network. See Section 2–4.
3. Maximum cable length of each Modbus network is 4000 feet. (See
notes on using repeaters to increase this range, Section 2–4. Also,
see the note regarding substation installation in Chapter 3.)
4. All Modbus IEDs attached to a single RS-485 network must
communicate at the same baud rate. (See Table 1 for Modbus
IEDs’ communication speeds.)
5. RS-485 cable shields must be properly grounded. For maximum
protection against surge and EMI damage, each IED on the
network should have an isolated ground connection. See Section
2–4, Modbus rule 4, for an example of proper RS-485 wiring and
grounding. Also, see the note regarding substation installation in
Chapter 3.
Table 2. Host PC configuration rules.
3 The following RS-485 interface card is recommended for providing the RS-485 connection at the host PC. If any other serial card is used, PMCS
requires that the communications driver be compatible with the MS Windows serial communications protocol. Please refer to Section 3–1 for
information on the special termination requirements of the RS-485 card.
Manufacturer Description
Quantity/8 ports
Part, Order Number
Connect Tech, Inc. Intellicon-Flex8 RS-485 card 1 I4808064XXNC
Intellicon/DFLEX SLIM 4 SIMMS
8 Port, DB9 I/O Box 1 IOB08DB9
4 The following RS-232/RS-485 converter is recommended for providing a single RS-485 connection at the host PC.
Manufacturer Description Part, Order Number
Multilin RS-485/RS-232 Converter F485120
When using the above RS-232/RS-485 converter, remember that the converter has DIP switches inside that determine its baud rate. Switch group 3
should be set according to the baud rate at which the converter is to be used. Refer to the converter’s documentation for further information.