GE PQMII Instruction Manual page 46

2–18
indicates that the PQMII is transmitting data. Each PQMII must be daisy-chained to the
next one as shown in the figure below. Avoid star or stub connected configurations. If a
large difference in ground potentials exists, communication on the serial communication
link will not be possible. Therefore, it is imperative that the serial master and PQMII are both
at the same ground potential. This is accomplished by joining the RS485 ground terminal
(Terminal 46 for COM1; Terminal 49 for COM2) of every unit together and grounding it at the
master only.
The last PQMII in the chain and the master computer require a terminating resistor and
terminating capacitor to ensure proper electrical matching of the loads and prevent
communication errors. Using terminating resistors on all the PQMIIs would load down the
communication network while omitting them at the ends could cause reflections resulting
in communication errors. Install the 120 Ω, ¼ watt terminating resistor and 1 nF capacitor
externally. Although any standard resistor and capacitor of these values are suitable, these
components can also be ordered from GE Multilin as a combined terminating network.
Each communication link must have only one computer (PLC or DCS) issuing commands
called the master. The master should be centrally located and can be used to view actual
values and setpoints from each PQMII called the slave device. Other GE Multilin relays or
devices using the Modbus RTU protocol can be connected to the communication link.
Setpoints in each slave can also be changed from the master. Each PQMII in the link must
be programmed with a different slave address prior to running communications using the
S1 PQMII SETUP COM1 RS485 SERIAL PORT
Multilin EnerVista PQMII Setup Software may be used to view status, actual values, and
setpoints. See 4.4: Using the EnerVista PQMII Setup Software for more information on the
EnerVista PQMII Setup Software.
PQM II
RS485.CDR
FIGURE 2–13: RS485 Communication Wiring
CHAPTER 2: INSTALLATION
MODBUS COMMUNICATION ADDRESS
GE Multilin
IED
SR Series
GE Multilin
Protection Relay
PQMII POWER QUALITY METER – INSTRUCTION MANUAL
setpoint. The GE
PQM II