Endress+Hauser Micropilot FMR20 - Page 27

Micropilot FMR20 Modbus RS485 Electrical connection
Endress+Hauser 27
DO / A(+)
+
D1 / B(-)
-
1
+
-
3
2
4
DO / A(+)
D1 / B(-)
A0038149
 20 Block circuit diagram for Modbus RS485 connection, multiple users
1 Power supply
2 Device with Modbus communication
3 Bus termination
4 Modbus master/RTU
The bus cable should be a type-A fieldbus cable with a maximum length of
1 200 m (3 937 ft).
If the device is installed in a hazardous environment, the cable length may not exceed
1 000 m (3 281 ft).
A terminating resistor must be connected at both ends of the RS485 bus.
6.3.2 Modbus RS485 bus terminating resistor
The bus terminating resistor should be installed as per the RS485-IS specification.
200 Ω
510 Ω
510 Ω
-
+
DO / A(+)
D1 / B(-)
A0038150
 21 Representation of the bus terminating resistor as per the RS485-IS specification