Modbus to Ethernet

Dale87

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Feb 2022
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Illinois
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What's the cheapest way to go from modbus rtu rs485 to Ethernet IP or TCP. I've got some power transducers I'd like to read some modbus addresses, they're only rs485. I've only got fiber located where they're installed so to get it back to either the HMI or PLC id have to go IP or TCP. A lot of places make a converter but most are $1,000+ dollars. The power transducers are only $300.

Thanks
 
Same answer as I always give, S7-1211. Although it doesn't have RTU onboard, so you'd need either a communications module or a communication board for RS 485, which would probably push it over the price of the above post from Ken Roach. May be worth it if there's a chance you need the additional functions in that location.
 
Moxa Nport models (if you can read Serial over TCP modbus protocol)
Moxa Mgate (Modbus TCP)
Teltonika TRB245 or TRB255 (Modbus TCP)
 
Especially if you already have an enclosure with space, cheap but not the absolute cheapest: Micro 820 or Click. That also gives you a bit of I/O that might be useful. I would probably use Click C0-11DD2E-D ($212, or relay outputs for $4 more) for that unless I had a reason to use an analog model ($253-$269) for some additional monitoring in the area. The 820 would cost a bit more and depending on the application, maybe should also use an isolated serial module instead of the on-board port. Add a power supply as needed for a bit more cost.
 
Last edited:
I would definitely use the Click Plus.

Software is free, it supports runtime updates (~online editing).
They're reliable and well supported.
You can write logic to manipulate the data as needed for your application.

I would not use a Micro8x0. I had my first experience working with one of those this week where all I needed to do was add a single new remote node to a gateway system for radio telemetry done by others. The programming looked straightforward, but making the changes was quite a PITA. First I had to download and install the latest version 13.0 of CCW which took an hour.

Then I had to study how the data types for the MSG_MODBUS work and it is a little weird. Then I had to study what the differences are between Logical Values, Physical Values, and Project Values so that I could determine how and if I needed to edit the numbers associated with the instructions I copied and edited.

Then I had to add entries to the Ethernet Modbus Map for the TCP side and sort out the data types for each.

I could not do any of this live because I am not paying for the developer version, so I googled how long the PLC might be stopped for a download and was shocked. It was not a problem for this job and took less than 2 minutes since the program is so tiny, but that is still absurd.

Not a fan.
 
OkiePC said:
I would definitely use the Click Plus.

Software is free, it supports runtime updates (~online editing).
They're reliable and well supported.
You can write logic to manipulate the data as needed for your application.

I would not use a Micro8x0. I had my first experience working with one of those this week where all I needed to do was add a single new remote node to a gateway system for radio telemetry done by others. The programming looked straightforward, but making the changes was quite a PITA. First I had to download and install the latest version 13.0 of CCW which took an hour.

Then I had to study how the data types for the MSG_MODBUS work and it is a little weird. Then I had to study what the differences are between Logical Values, Physical Values, and Project Values so that I could determine how and if I needed to edit the numbers associated with the instructions I copied and edited.

Then I had to add entries to the Ethernet Modbus Map for the TCP side and sort out the data types for each.

I could not do any of this live because I am not paying for the developer version, so I googled how long the PLC might be stopped for a download and was shocked. It was not a problem for this job and took less than 2 minutes since the program is so tiny, but that is still absurd.

Not a fan.
Click to expand...


I use them "micro 8××" on the "slave" end of telemetry projects where I just need a few IO. Absolutely awful, I shake my head every single time, and ask myself why I did it......
 
I do not understand the question.

What is Ethernet IP ?

Do you mean Rockwell's EtherNet /IP protocol?

What does TCP mean? TCP is a transport layer protocol and will not be helpful by itself.

We know that the power meters use Modbus RTU over RS-485, which you clearly specified. But what is the protocol you are converting to/from?
 

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