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Thursday, September 19, 2019
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Using Modbus to Send Data Across to Two PLCs Belonging to Two Different Networks
Need to establish serial commmunication with two PLCs of different networks.

I am having two PLCs belonging to two different IP networks. Now there is a need to share data across these two PLCs. Which are separated by 1.5km distance. Can I achieve it with modbus over serial communication? Using fibre optic as the media?

Moderator’s Note: The author has checked GE Mark V/VI as the vendor

>two different IP networks.

Presumably, you mention RS-485 because the PLCs each talk Modbus RTU over RS-485. An RS-485 port is not concerned with IP (Ethernet) addresses.

>Now there is a need to share data across these two PLCs. Which are separated by >1.5km distance. Can I achieve it with modbus over serial communication? Using fibre
>optic as the media?

If one of the PLCs has Modbus RTU master functionality and the other is a Modbus RTU slave, then, yes, you can find commercial RS-485/Fiber Optic (or RS-232/FiberOptic) converters that will handle the hardware link, depending which serial port is available for the Modbus port.

Modbus is NOT standard on PLC's, you need to investigate the availability of Modbus and whether there is master functionality on one end and slave functionality on the other end.