KROHNE MFC 010 C Converter - Manual (Page 19)

MFC010 Interface Manual 17
4.3 Connection To The Modbus Bus
When installed in hazardous area application the MFC010 i nterface i s not di rectly c ompatible with t he
Modbus interface standard due to the presence of the required Zener Barrier devices.
In a poi nt-to-point configuration, when the MFC010 is the only device on the bus, the cable length from
the barriers to the “Master” host system must not exceed 10m in length. If a greater distance is required,
the us e of a s uitable R S485 repeater is recommended, in which case the repeater connection to the
Zener B arrier dev ices s hould not ex ceed 10m i n l ength. T he m aximum c able l ength bet ween t he
Repeater and the “Master” host system is determined by the operating limits of those two devices. T he
cable length from the Modbus barrier device to the MFC010 must be less than 300m i.e.
Where the distance from the barrier device to the MFC010 is less than 10m, two barrier devices may be
connected in parallel to the “Master” host system, or the repeater if one is being used, refer to the diagram
below. The overall cable length from the Host/repeater to the barrier devices must still be less than 10m
as described previously. If more than two devices are required to be connected then a dedicated repeater
should be used for each.
Each MFC010 MUST have its own dedicated barrier interface; they MUST NOT be connected in parallel
on the hazardous area side of the system.