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Networking conundrum with a 120 & 230

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Hi all,

A new forum member but have used small Unitronics gear on and off over the years. Question is a bit involved but please bear with me.

I normally only work with standalone controllers, but I have a situation where I am going to be using two controllers and IOs that I already possess and may as well use…a V230 and a 120. I have an Ethernet card for the 230. Both PLCs are going to be using analogue IOs as well as digital. Having two controllers is best from a redundancy aspect in that the two main plant rooms will have a controller in each. The setup is controlling a small but complex pump, valve and power system.

The issue I have is that I have to work around existing cable limitations tying in to the lack of Ethernet port for the 120. Both plcs have to be able to be accessed via remote. I have looked up programming examples a bit, but perhaps the easiest solution is if I pose my situation to the forum where hopefully someone can give me quick answers that won’t take too much of their time.

The cable problem is that I only have 2 free cat5 runs between where the 2 controllers have to go. 1 end is near the router that will provide remote access. The other end is 80m away, which tests fine on Ethernet and also using the cat5 as 485. Owing to very full and awkwardly placed conduits, I simply cannot run any new cable between the endpoints, so Canbus on dedicated cabling is not possible although it would have saved me having to post this!! I only need to be transferring around 6 words of data b/n the two controllers in both directions, and speed isn’t essential. It is just so that some info can be seen and perhaps acted on at either end. So what will be the best layout? It’s a bit of a conundrum! I have the following ideas:

1). The 230 or 120 at either end, with the 230 on Ethernet and the 120 connecting by a serial to Ethernet/wifi adapter, but can communication between the two happen over this style of link? As in Ethernet talking to an essentially much slower serial conversion that is still ethernet? I could possibly use some spare pairs in the unused cat5 line to do digital signals b/n the two controllers to say a particular communication was happening/should happen etc.

2). The 120 at the far end, linked to the 230 by 485 with the 230 on Ethernet for remote access. However, my understanding is that I cannot remote access via Ethernet any controller linked by 485, although I can set up transfer of data b/n the two on 485.

3). Perhaps a variation of no. 1 where the controllers are linked by 485 for intercommunication, and I also have the serial to Ethernet adapter on the 120 to let me get into it remotely as well as the 230 by its native port. This one seems the most likely to me.

4). Somehow run canbus on the cat5, although everything I’ve read says this is not possible.

5). Put your suggestion here!!

Trusting that you can see my puzzle! But don’t let me take too much of your time! This is not an urgent job and I will likely only check the forum/post once a day, so please don't be offended if I don't answer immediately.


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I'm with Emil. Don't use a V120 on a new installation - use a V130 and get the Ethernet card for it. You can always put an additional Ethernet switch anywhere you want to and get additional Ethernet ports in the panel.

Ethernet is so much easier to implement over RS485 or CANbus unless you have a distance or speed issue. If you need to throw data between the controllers you can use the Modbus IP blocks.

Joe T.

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Thanks Joe and Emil,

I agree a 130 would make it far simpler, but the issue is that I already have the 120 and 230. I had a job a few years ago that got changed, leaving me holding a fair few items....grr grr. This install is actually on my own property so I am just trying to save some $ as I have two of each controller along with a heap of IOs.

cheers from Aus,

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Hi Aus,

So we have established that you want to use existing equipment, and the items you have aren't the best choices from the point of view of a greenfield design.

To have remote access on both PLCs with minimum hassle, you are going to need an Ethernet to serial server.

To keep everything on an equal footing, i would get an Ethernet to RS485 serial server, and set up both PLCs on RS485. Make sure you choose an Ethernet to serial server that has a virtual COM port software utility and use this at the PC. In this case the Ethernet/Internet link becomes transparent and you just comm with the PLCs as if they were hanging off an RS485 port on your PC.

To handle comms between PLCs, looks like Modbus is the only option. I would use the second COM port on each PLC and the second CAT5 line to do this. Possibly then you need 1 or 2 RS485 to 232 convertors for the PLC(s), depending on their age.

As a backup I would put the V230 with Ethernet card in a position where it can be connected directly to the Ethernet end so you can connect the ethernet to that PLC as a backup if needed.

You could also use the ethernet port to connect to the V230 and stop modbus, so the single RS485 channel would then be available for remote connection. However, that would not allow you to debug PLCs with the Modbus running.

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Thanks for your very helpful suggestions Simon,

I know this is a dumb question, but is it ok to operate a 230 without a snap-in and just be connected to IOs via the expansion port? It has just occurred to me that this would give me simple ethernet only connections using the two 230s I have, instead of one 230 and one 120, but I have always thought they needed to have the snap-in attached.

From what Emil and Joe say it appears that ethernet is easier to set up and this way I would only need to get one 19-ET1.

Call me chicken, but I don't want to try running the 230 without the snap-in without someone telling me it's ok! I can't find anything about this in anything I've seen so far, but it's probably in a manual somewhere. Visilogic doesn't seem to mind it as a build config.

cheers from Aus.

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Hi Aus,

Definitelly - you can use V230 without Snap In module!

You can use it without any I/O at all - just as inteligent HMI, communication center and/or Data Logger.

You can add to it Snap In module only.

You can connect Expansion modules only - without Snap In.

You can connect and use both - Snap In AND Exapnsion modules.

All these options are fully legal and it's a matter of project needs and ... personal preferences!

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Thanks Emil, and everyone else for their input.

I think that I'll go down the 2 x 230 on ethernet path as it looks to be the easiest. I'm sorry I didn't think to ask about snap-ins in the first place...brain stuck on a misconception. This solution is a bit like that elegant bit of programming you've done. You work on the issue and eventually arrive at something far simpler and better than what you started with, then look at it and wonder why you didn't think of that in the first place! Learn something new every day, so thanks to all.

Cheers from Aus.

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