Today is...
Monday, April 24, 2017
Welcome to, the global online
community of automation professionals.
Featured Video...
Featured Video
Watch an animation of a conveyor stacking operation demonstrating the use of a move on a gear command.
Our Advertisers
Help keep our servers running...
Patronize our advertisers!
Visit our Post Archive
Modbus and Media Converter
Make a Modbus Bus in two regions by use of optic connection between them.


I faced a situation in a project as below:

there are 3 energy meters (EDMI MK6E) in a power plant, and there are also 5 energy meters (EDMI MK6E) in the substation of power plant in 300 meters distance. I want to make a Modbus bus with all 8 energy meters.

first i make a bus with 3 meters in the power plant, and then i convert the signal to optical by use of an appropriate media converter. then i transmit the optical signal to the substation, and reconvert it to copper mode, and make another bus with 5 meters in the substation (all meters would be in one bus). after that i convert the output again to optical domain and transmit it to the upper substation by fiber optic.

I want to know that is this approach possible?

The user manual the comes up in a web search for EDMI MK6E is dated 2004 and shows serial connections: RS-232 or RS-485. One model appears to use RJ-45 connectors for the RS-485, but the word Ethernet does not appear in the manual, so the network is apparently an RS-485 multidrop network.

A pair of RS-485-to-fiber optic converters (one in the power plant, one in the substation) just replaces copper wire with advantage of providing electrical isolation, so yes, an extended RS-485 network bus you describe should function OK.

The end result is not two network busses, but one long network bus extended in the middle by a pair of optical converters.

By automationtechie on 18 April, 2017 - 5:35 pm

This is a very common application. Fiber Optic cables are often used to bridge large gaps and increase network speed in serial networks by allowing for faster baud rates to be used. This is due to signal strength issues. For your Modbus application, you simply need to extend the RS-485 network at a convenient point. You can use 2 of our I-2541 modules and a multimode fiber optic cable to accomplish this.

For detailed information, you can see the application diagram on page 3.