KROHNE CORIMASS MFC 85 Interface EN - Manual (Page 27)

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4. Using the Current Output with the Modbus
The MFC 081/085 Converter is fitted with one current output in addition to the Modbus
connection. This current loop is connected between terminals 6, lout, and 5, 0 volts (refer to
the normal Installation and Operating manual). However extra care must be taken when
connecting this output.
The MFC 081/085 output circuitry is fully floating. It is galvanically isolated from protective
earth, PE and from the converter’s power supply. (See below).
Terminating and
biasing resistors
If just the Modbus is connected then the converter’s output circuitry will float to the potential of
the bus. However the current output shares a common 0 volt reference with the Modbus
output and hence also with the bus. The current loop receiver must therefore have a fully
floating input. If not it will try to drag the Modbus to some potential of its own. This could in
turn result in interference with stable operation of either, or both of the current loop and the
Modbus.
5. Converter Configuration
Setting up the Modbus System:
Use the 3.11.0 Serial I/O menu to set up the Modbus communications:
Fct. 3.11.0 Serial I/O
Fct. 3.11.1 Protocol
Select “MODBUS”
Fct. 3.11.2 Address
Enter an address number between 1 and
247. The converter will only respond to
Bus messages which have a matching
address.
Fct. 3.11.3 Baudrate
Select the required communications
baudrate from the following list:
1200, 2400, 4800, 9600, 19200 and the
data format from
E81,E82,O81,O82,N81,N82.
N=no parity: E=even parity: O=odd parity
1 or 2 stop bits