PowerMonitor 1000 Unit 21
Rockwell Automation Publication 1408-IN001E-EN-P - September 2013
Serial Communication
Use point-to-point wiring between one power monitor and a computer or other data terminal
for HyperTerminal communication and DF1 full-duplex communication. DF1 half-duplex,
Modbus RTU and DH-485 protocols permit a point-to-point or multi-drop network
configuration.
Multi-drop RS-485 communication wiring should be installed in a daisy-chain configuration.
Up to 32 nodes may be connected together in a network. We recommend the use of Belden 9841
two-conductor shielded cable or equivalent. The maximum cable length is 1219 m (4000 ft).
Use of a star or bridging topology is not recommended and may result in signal distortion unless
impedance is matched for each spur (star topology) or network (bridge topology).
You must provide a RS-232 to RS-485 converter for communication between the power
monitor serial port and an RS-232 port in an external device such as a computer or
programmable controller. Examples of converters include the following.
• Allen-Bradley® catalog number 1761-NET-AIC
• B&B Electronics, Inc. part number 485SD9TB (DB-9 connection)
At one end of each cable segment, connect the cable shields to the SHLD terminal of the power
monitor serial port or converter. The SHLD connection provides a low-impedance ground for
high-frequency noise while attenuating DC or line-frequency signals.
If needed, install 150 , ¼ W terminating resistors at the ends of the daisy-chain cable. Some
RS-485 converters are equipped with internal terminating resistors. Contact the manufacturer of
the converter for additional information.
See Use Communication to Set Up
on page 38 for information on configuring serial
communication parameters such as data rate and node addresses.
Wiring to the power monitor RS-485 port is the same as wiring to the PowerMonitor 3000 native RS-485 port.
