Communications 5-7
3300 ACM Installation and Operation Manual Power Measurement Ltd.
5.9 PLC/AB COMPATIBILITY
The PLC/AB option for Power Measurement’s 3300 ACM
Digital Power Meter allows access to the Allen-Bradley Data
Highway Plus (and Data Highway) through use of the Allen-
Bradley Full Duplex DF1 Protocol. The 3300 ACM PLC/AB
emulates two commands from the PLC2 command set:
Unprotected Read and Unprotected Write. The Full Duplex
DF1 protocol allows information and data to be efficiently
transferred between an A-B PLC and a 3300 ACM. The
PLC/AB option allows all real-time parameters, as well as
kW total demand, kVar total demand, kVA total demand,
and Amps average demand parameters for the 3300 ACM, to
be accessed.
Mechanical mounting, electrical wiring (other than communi-
cations), and operation of units with the PLC/AB option is
similar to that of the basic 3300 ACM.
Communications wiring requirements are discussed in
Chapter 2.6, “Communications Connections”.
Hardware Requirements and Wiring
The 3300 ACM interfaces to the Data Highway via Allen-
Bradley Communication Interface Modules. The two modules
that the 3300 ACM communicates with are the 1770-KF2
Series B Communication Interface Module and the 1785-KE
Series B Data Highway Plus RS-232C Communications
Interface Module.
MULTI-DROP
A multi-drop communications topology allows you to connect
up to 128 3300 ACMs to the data highway via one A-B
communication interface module using RS-485 communica-
tions. A Power Measurement COM32™ or COM128™
RS-232C to RS-485 Converter is required for multi-drop
systems (see Figure 5.9.1).
NOTE
Refer to converter manual for detailed in-
formation regarding configuration.
Communications Protocol
All communications between the PLC and 3300 ACM(s)
conform to a master/slave scheme. Information and data is
transferred between a master PLC and slave 3300 ACM(s).
The following message packets are supported:
READ OR WRITE SETUP
Allows the PLC to read or define all the user-programmable
setup parameters in the 3300 ACM.
READ LONG OR SHORT REAL-TIME DATA
Allows the PCL to read detailed (long) or condensed (short)
realtime data measured by the 3300 ACM.
CLEAR KW OR KVAR HOUR
Allow the PLC to clear the kW hour or kVAR Hour counter of
the 3300 ACM.
For more information regarding operation with the A-B
communications protocol, refer to the Power Measurement
document: 3300 ACM/Allen-Bradley Serial Communications Protocol.
Figure 5.9.1 PLC/AB Communications Connections
1770-KF2
Asynchronous Port
(RS-232C)
SHLD 1
TXD 2
RXD 3
RTS 4
CTS 5
DSR 6
GND 7
DCD 8
DTR 11
1 SHLD
2 RXD
3 TXD
4 RTS
5 CTS
6 DSR
7 GND
8 DCD
20 DTR
Converter
RS-232C Port
50 feet maximum
25-pin
Male
Connector
25-pin
Male
Connector
1785-KE
RS-232C Port
Converter
RS-232C Port
15-pin
Male
Connector
SHLD 1
TXD 2
RXD 3
RTS 4
CTS 5
DSR 6
GND 7
DCD 8
DTR 11
GND 13
1 SHLD
2 RXD
3 TXD
4 RTS
5 CTS
6 DSR
7 GND
8 DCD
20 DTR
25-pin
Male
Connector
50 feet maximum
Courtesy of NationalSwitchgear.com
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