Communications 5-5
3300 ACM Installation and Operation Manual Power Measurement Ltd.
Figure 5.8.1 Modbus Communications Connections
NOTE
A 3300 ACM operating in Modbus mode
will not be compatible with Power
Measurement's M-SCADA / L-SCADA
system.
Hardware Requirements and
Communication Wiring
Mechanical mounting, electrical wiring (other than communi-
cations), and general operation of units communicating on
the Modbus are similar to that of the standard 3300 ACM.
The 3300 ACM is connected on an RS-485 network that is
interfaced to the Modbus via an RS-232C to RS-485 converter,
such as Power Measurement's COM32
TM
. A Modicon BM85
Bridge/Multiplexer is required between the Modbus and
Modicon Controller.
A multi-drop topology allows up to thirty-two 3300 ACMs on
an RS-485 network to be connected to each of the four BM85
Bridge/Mux ports. This allows for up to 128 power meters to
be connected to each BM85 (refer to Figure 5.8.1).
1 SHLD
3 TXD
2 RXD
7 GND
20 DTR
6 DSR
4 RTS
5 CTS
SHLD 1
RXD 2
TXD 3
GND 5
DTR 4
DSR 6
RTS 7
CTS 8
COM32
RS-232C Port
Bridge/Mux
Modbus Port
25-pin Male
D-Type
Connector
9-pin Male
D-Type
Connector
50 feet maximum
Twisted Pairs
Modicon AEG
Modbus
Plus
To other Modbus networks (4
networks total with 32
devices per network)
Modbus
Plus
RS-232C
Port
Modbus
Ports
MODICON 984
CONTROLLER
MODICON BM85
Bridge/Mux
(DCE)
(DTE)
3300 ACM
To other 3300 ACM devices
(32 total possible)
3300 ACM
RS-485
Network
COM32
tm
or COM128
tm
RS-232C to RS-485
Converter
NOTE
For detailed information regarding
confi-guration of the COM32 or
COM128 inter-faces, refer to the
manual for the device.
5.8 MODICON MODBUS
COMPATIBILITY
The 3300 ACM provides compatibility with the Modicon
Modbus system as a standard feature, selectable from the
front panel. The Modbus communications protocol allows
setup parameters and measured data to be efficiently trans-
ferred between a Modicon Programmable Controller and
multiple 3300 ACMs. The 3300 ACM performs Modbus
communications by emulating a Modicon 984 Controller.
All measured data for the 3300 ACM can be accessed via
Modbus, including all real-time, thermal (running) or sliding
window demand, and minimum/maximum registers.
Polarity of power measurements can be determined through
six polarity registers. All setup parameters are also accessible.
Password protection is provided via a special password
register location.
The 3300 ACM Modbus protocol supports standard 16 bit
registers, as well as 32 bit extended registers. 32 bit registers
would typically be required only for large energy values (e.g.
KWH, etc.) Register size is selectable from the front panel.
Courtesy of NationalSwitchgear.com
To Next Page
Loading...
Need help?
General
