Looking for suggestions for PoE Modbus Converters for PLC comms

PLCGuy2020 · Apr 21, 2020

I'm gonna be using an EN2T to talk to a couple of Modbus RTU devices using Rockwell's Modbus Server code base. I'm trying to find PoE serial converters so I can put them inside other vendors cabinets and just run less cable overall. I'm not finding a lot of good solutions however so I'm wondering if anyone's had any luck with anything specific? Moxa and ******* don't seem to offer anything that's PoE however...

Firejo · Apr 21, 2020

I'm not so sure what you are wanting to do can be done. If I'm not mistaken, the AB Modbus code is for Modbus TCP (and is very complicated to get working). Going from Modbus TCP to Modbus RTU is not just converting Ethernet to serial. That said, the other problem you're going to run into is Ethernet to serial servers typically require redirect software running on a PC.
What you are trying to do is typically done via a protocol bridge. Spectrum and RTA both make them (as well as others).

PLCGuy2020 · Apr 21, 2020

If the PLC sets up a proper socket connection than it can be done. I talked with Rockwell support and as long as the converter supports true Socket communication then it'll work.

Wait why did the forum censor COM TROL

Dravik · Apr 21, 2020

The perle IOLAN line has some serial to ethernet converters that will do POE
https://www.perle.com/products/iolan-stg-poe-terminal-server.shtml

Dravik · Apr 21, 2020

They also do the modbus gateway thing to make the RTU-TCP conversion easier.

Ken Roach · Apr 21, 2020

I cringe a little every time somebody wants to use that Modbus code, especially when they blithely tell me that Tech Support has endorsed it. It's my understanding that they provide no application troubleshooting support if that code is modified at all... it's an example, no more.

How much data are you reading and writing ? Do the Modbus/RTU devices have RS-232 ports, or RS-422, or RS-485 ?

That's a great link to those Perle serial servers; I wasn't aware of their PoE offering. But I don't see that the ones that convert Modbus/TCP to Modbus RTU are also available in a PoE version.

I would have to be looking at a major cost savings to sink the time into installing and testing a Modbus TCP/RTU -> Logix interface with the raw socket logic instead of grabbing something off-the-shelf from HMS, Red Lion, Real Time Automation, or GridConnect.

Ken Roach · Apr 21, 2020

Edit: I see the Perle IOLAN technote about Modbus gateway functionality, and would be pleased to hear it verified that it's included in the PoE units.

https://www.perle.com/supportfiles/modbus_gateway_technical_note.shtml

Contr_Conn · Apr 21, 2020

Firejo said:
I'm not so sure what you are wanting to do can be done. If I'm not mistaken, the AB Modbus code is for Modbus TCP (and is very complicated to get working). Going from Modbus TCP to Modbus RTU is not just converting Ethernet to serial....

I concur that Modbus TCP and Modbus RTU data packets are not the same, so you technically need a protocol converter.
As for RA code, did you try new Modbus AOIs recently posted? Much easier to use than old code and not buggy.

PLCGuy2020 · Apr 24, 2020

Contr_Conn said:
I concur that Modbus TCP and Modbus RTU data packets are not the same, so you technically need a protocol converter.
As for RA code, did you try new Modbus AOIs recently posted? Much easier to use than old code and not buggy.

I got the new code for work within half an hour of installing it and grabbing my first register. It works supprisingly well.

Contr_Conn · Apr 24, 2020

From my experience new Modbus AOI code is not just easy to configure, all commands are actually work, no minor overflow faults or major controller faults by going out of boundaries.
Also there are no hard limits on the amount of connections and transactions, scalable solution with small memory footprint.

Firejo · Apr 24, 2020

Ken Roach said:
I cringe a little every time somebody wants to use that Modbus code, especially when they blithely tell me that Tech Support has endorsed it. It's my understanding that they provide no application troubleshooting support if that code is modified at all... it's an example, no more.

How much data are you reading and writing ? Do the Modbus/RTU devices have RS-232 ports, or RS-422, or RS-485 ?

That's a great link to those Perle serial servers; I wasn't aware of their PoE offering. But I don't see that the ones that convert Modbus/TCP to Modbus RTU are also available in a PoE version.

I would have to be looking at a major cost savings to sink the time into installing and testing a Modbus TCP/RTU -> Logix interface with the raw socket logic instead of grabbing something off-the-shelf from HMS, Red Lion, Real Time Automation, or GridConnect.

Spectrum Controls makes a pretty good device as well (very easy to use)

Looking for suggestions for PoE Modbus Converters for PLC comms

PLCGuy2020

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Firejo

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Dravik

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Ken Roach

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Contr_Conn

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PLCGuy2020

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Firejo

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