Communications 5-1
3300 ACM Installation and Operation Manual Power Measurement Ltd.
5. COMMUNICATIONS
5.1 INTRODUCTION
The 3300 ACM is equipped with an RS-485 communications
port which allows the 3300 ACM to be integrated within large
energy monitoring networks. The communications port is
optically isolated and transient protected, and can operate at
baud rates up to 19,200.
The 3300 ACM is fully compatible with Power Measurement’s
PC-based M-SCADA or L-SCADA systems. M-SCADA / L-
SCADA can display all measured parameters provided by the
3300 ACM. M-SCADA / L-SCADA can also be used to
remotely program all setup parameters. An open communica-
tions protocol allows similar access by third-party systems,
including the Modicon Modbus.
This chapter provides additional information regarding
remote communications connections, programming, and
general operation.
Firmware Updating via the Comm. Port
Future 3300 ACM firmware updates, when made available by
Power Measurement, can be quickly performed via the RS-485
port; therefore, it is strongly recommended that all 3300 ACM devices be
connected onto a communication bus when installed, even if remote
communications are not initially required. Updates are performed by
downloading of new firmware code from a locally connected
host computer, or a remote computer connected via modem or
other method.
5.2 RS-485 COMMUNICATION
RS-485 communication can be used to concurrently connect
up to thirty-two remote devices on a single communications
loop. Each device is given a unique UNIT I.D. (identification
number). In this way, each remote device may be monitored
and controlled from one location by a single computer/PLC.
The total distance limitation on a single RS-485 communica-
tion network is 4000 feet (1219 meters) using 22 AWG
(.4mm
2
) twisted pair shielded cable. Chapter 2 provides
wiring diagrams for RS-485 network connection.
Communication methods between the remote RS-485 site and
the master computer station can include a direct RS-485
connection (under 1219 meters), telephone lines with mo-
dems, fiber-optic and/or radio links (see Figure 5.2.1). An RS-
232C to RS-485 converter, such as Power Measurement’s
COM32 or COM128, is required between the RS-232C port of
the computer or modem and the RS-485 network (see Chapter
2).
RS-232 / RS-485
CONVERTER
RS-485
RADIO
LINK
FIBER OPTIC LINK,
LEASED PHONE LINE
or DEDICATED CABLE
SITE 1
SITE 2SITE 3
RS-232 / RS-485
CONVERTER
RS-232 / RS-485
CONVERTER
LOCAL RS-485 LOOP
SUPPORTS UP
TO 32 DEVICES
LOCAL RS-485 LOOP
SUPPORTS UP
TO 32 DEVICES
LOCAL RS-485 LOOP
SUPPORTS UP
TO 32 DEVICES
TEL or FOTS
MODEM
TEL or FOTS
MODEM
RADIO
TX/RX
MODEM
MODEMRADIO
TX/RX
UP TO 4000 FT.
Figure 5.2.1 Remote Communication Methods
Courtesy of NationalSwitchgear.com
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