Rs485 Interface, Electrically Isolated - Honeywell Elster EK280 Applications Manual

EK280

6.4.3 RS485 interface, electrically isolated

6.4.3.1 Wiring
i
When the EK280 is connected to a RS485 bus there must be no terminal resistors connected to
the bus!
Due to the current limit for intrinsically-safe apparatus approval, the EK280 cannot supply sufficient current to
power terminal resistors. At the data transfer rate used, terminal resistors are not required.
6.4.3.1.1 Four-wire full duplex - wiring
EK280
6.4.3.2 EK280 jumpers
X6: No jumper
or one jumper on the pins located
near the terminals
If a connected RS232 interface device has a direct or capacitive ground potential connection, there is a risk
of interference coupling via ground loops, which may affect pressure or temperature measurements. The
position of the two jumpers on X5 means that the EK280 interface is electrically isolated from the rest of the
circuit and therefore electromagnetic interference coupling is prevented.
To power the decoupled EK280 interface a voltage of between 5 and 8 volts (3 mA approx.) must be
connected to the "Ri" and "GND" terminals.
Application Manual
T-
T+
R-
R+
Ri
GND
Uext+
Uext-
X5: No jumpers
or two jumpers on the pins located
near the terminals.
("Park-Position")
R-
R+
Bus Master
T- RS485
T+
+
5...8V (DC)
-
+
Power supply
- 8V (DC)
T-
T+
Further
R- Bus participants
R+
57