Modbus RTU on 485 to ModbusTCP on Fiber converter


Thread Starter


Trying to take a modbus RTU signal from an existing series of Electrical Utility Meters and send it along the existing fiber backbone.

Has anyone had any success with converters from Modbus RTU (on a 2 wire 485) to Modbus TCP (on Fiber)? We tried with a B&B electronics Vlinx (model# MESR901-SC) - no luck!

Lynn August Linse

It should be no harder to convert Modbus/RTU to Modbus/TCP on fiber than on wired Ethernet, something I've enabled on probably close to a million devices.

If the B&B didn't work, then likely either:

1) your RS-485 was wrong - did you handle the 'signal ground' correctly? I can imagine electric meters would have potentially skewed grounds.

2) your fiber optic was wrong (wrong sizes/types/terminations). Fiber optic can be one of the hardest new technologies to learn & use unless you have long experience with it and/or very expensive test equipment.

You may find it easier to take a "Brand X" Modbus/RTU to wired Ethernet unit to eliminate any misunderstanding of the RS-485 or Modbus bridge function - in your case that would be a B&B Vlinx device for wired Ethernet.
Thanks for the reply!

All of the things you suggested were done many times :)
After a call to B&B, they determined the item defective.

It should have been a fairly straight forward install, but since we were not getting a signal on the head end we thought it was a physical layer issue in the wiring, which it was not.It really through us for a loop, sending us scrambling.

We eventually used a 485 to fiber Media converter( SerialComm) and the system worked fine.
in that case, did you have one converter to convert modbusRTU to modbus TCP and sent over fiber optic (same converter)?

we have this, modbus tcp CONVERTER 1 modbus serial CONVERTER 2 fiber optic....we use 2 converters to do the conversion....

i am asking, if you succeeded in just using one converter to do such conversion...can you show me where to get such converter...?
Hi Nuban, BauPow

We have our standard protocol converter(just one converter would do the job) SYNC 2000S6F1 to meet this requirement to convert modbusRTU to modbus TCP and send over fiber optic

Do contact me for more details on SYNC 2000 capabilities and features

Thanks and best regards,
Gautam Bhat
[email protected]
> Yes, I think you can contact gautam.bhat(at) for further details

I have good experience with kalkitech, in addition to deliver what they say. This wasn't exactly the same converter your talking about, but a profibus to modbus RTU conv. they also included a communication sniffer to make sure everything is running smooth. I had to prove a customer that the equipment i delivered was working properly cause some other company delivered the system we controlled and they wrongly accused me of setting a wrong single point command address. So i just logged on to the kalkitech unit and logged communication when triggering command, voila, i was right, they were in the s%$t pile :)

Customer's happy, I'm happy, kalkitech is very nice <3