18
NOTE!
In networks with a nominal voltage of 1000 V or more, the regulations call for the current
transformer circuits to be earthed. At lower voltages, this is not required, but is nevertheless
recommended.
All the S2 terminals, for example, can be commoned to earth, but it must be checked beforehand
whether the current transformer circuits are already earthed in the Installation.
In general, it is recommended that all current transformer circuits be earthed.
In networks with a nominal voltage of 1000 V or more, damage may occur to the instrument if the
circuits are not earthed.
5.1.3 Ethernet connection
The EM-PQ 2300 has a shielded RJ45 jack at the top for connecting it to a hub or switch. Its pole
assignment corresponds to an MDI interface, so that a 1:1 cable must be used; Category 5 is
adequate. Possible transmission rates are 10 Mbit/s or 100 Mbit/s, half-duplex or duplex; the
EM-PQ 2300 automatically selects the highest possible setting.
CAUTION!
Incorrect network settings can cause network errors.
5.1.4 Connecting to the FRAKO Starkstrombus®, alternatively Modbus
Figure 7: FRAKO Starkstrombus
Field of application
The FRAKO Starkstrombus can be used for communication between a PC and the EM-PQ 2300, using either an
EMIS 1500 Central Unit (data collector and bus coupler) or an EMG 1500-PN Gateway (Ethernet bus coupler).
This is a practical solution if the FRAKO Starkstrombus is already installed and a direct connection via Ethernet is
not possible, otherwise the direct communication via Ethernet is preferable to that via the FRAKO Starkstrombus.
Connection
The EM-PQ 2300 uses an RS-485 interface at the terminals
‘BUS
A
,
,
B
’ to connect to the FRAKO
Starkstrombus. See Figure 7 on page 18.
Terminal
A
is commoned with all other
A
connections in the bus. Similarly, all
B
terminals are commoned, as are
all
terminals (no crossover of wires!). The shielding is connected to the
terminal.
The bus shielding (
) must be earthed at one
—and only one—point in the bus system. If earthing has not
already been done at some other point, it can be done at the EM-PQ 2300.
A bus topology (i.e. single line) must be used, with all devices wired in series or linked to the bus by drop lines no
longer than 2 m. Star topologies can be constructed using an EMB 1101 Repeater, available as an accessory.
The total length of the bus should not exceed 1000 m. An EMB 1101 Repeater must be installed to cover greater
distances.
The bus must be
earthed at one point
only!
Shielding
Shielding
Instrument at the
beginning or end
of the bus
120
Ω
Instrument
between other
devices on the
bus
