Modbus master / slave

[ScottyUK]

I have a developing problem - little now, but getting bigger by the moment - with two supervisory-level controllers which are supposed to be communicating via Modbus over TCP/IP. Neither system supports operation as a Modbus TCP/IP slave, only as a master. I am not aware of any direct means to make two masters talk to each other. I do not want to have to revert to a serial link if at all possible and am looking for a solution, which brings me to my question:

What I'm lamely hoping is that there is a third party device which can act as a Modbus slave to both controllers and act as a bridge to pass information between between these systems, effectively a buffer where one master writes data to the device and the other master reads it out? I don't really want to use a PC for this, a solid-state solution would be much preferred. I have some half-formed idea about using a PLC for this but can see that being overkill.

Am I looking for something which doesn't exist?


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If we learn from our mistakes I'm getting a great education!

 

[roydm]

Scotty,
How about this product?

http://www.redlion.net/Products/Groups/DataStationPlus/DataStationPlus/Docs/07034.pdf

I really like the Red Lion HMI, it looks much better and cheaper than the AB Versaviews I have been using
Roy

 

[slavag]

Hi Scotty.
Why not used simple PLC, as you wrote? For this porpuse we used AC500 ABB PLC, as slave for two masters. If I remeber right with two TCP/IP ports. If you would like, next week I check what we down exactly and will send you.
Best Regards.
Slava

 

[ScottyUK]

Thanks Roy,

That Red Lion product looks interesting . It is more or less what I had in mind, I think. I will have to go to their website and get a few more details of its capabilities. Have you used one of these before?


Hi Slava,

I am pleased you answered because one of the two masters is an ABB SCS-500. The other is an Emerson Ovation OCR400 controller. Did you have a similar problem to me?



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If we learn from our mistakes I'm getting a great education!

 

[slavag]

Hi Scotty.
What is a version of your SCS500?
Are you have in SCS optional line for Modbus TCP/IP? ( with old version we connect Modbus RTU on RS232 and RS485)
What data you would like send to/from SCS, digital or analog
(meas)? How much signals ( aprox )?
We had PROBLEMS with this issue. Isn't simple solution, but today we have some expirience. We make some procedure into SCS and build additional points into database for SCS. SCS wrote data to map of PLC and second Modbus master read it, same in other direction.
What is a tools you use for create database in SCS ( we use old Sigtool)?.
Best Regards.
Slava.
I haven't all data in the home, next week I'll send you more information

 

[ScottyUK]

Hi Slava,

I don't have all the details of the SCS-500 but it is a very new installation, less than a year old. We have a Modbus link running over TCP/IP from a second NIC installed in the SCS-500 computer to one of our turbine control system workstations (a Westinghouse / Emerson Westation) which is very stable. That link is running with the SCS as the master and the Westation as the slave. The Westation is part of an older system which is being upgraded but the new equipment does not give me the option for a Modbus slave configuration, so I have currently have two Modbus masters.

We're moving data for 12 bays: three analog points and about 15 digitals per circuit. I have some notes at work and I need to check the name of the tools we have been using. The SCS side of the link is something which ABB T&D at Stone, England have been working on with us and they have most of the expertise. I will post some more information on Monday.

I think you may have a solution developed which could help us out. Are ABB aware of the solution you have developed or is this something developed by a specific site?


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If we learn from our mistakes I'm getting a great education!

 

[slavag]

Hi Scotty.
You have option of OPC server.
Are you have SMS530 or MicroSCADA? MicroSCADA have OPC server, SMS530 maybe too. I suggest, that new turbine control system have it too. It's best solution, in one of our project, before one week we upgraded old SCS500 to new version with OPC server and would like upgrade link of Modbus TCP/IP berween two master too ( now it's via PLC).
From other hand, you need max send about 250 points and it only in one direction from SCS to turbine system.
And from my point of viewis enough our solution: simple PLC Modbus slave.
Don't check tools, it's new one,
Yes, we devoloped it for the specific site, but ABB haven't any problem with this solution, actually isn't ABB issue.
It's work fine for the 3 years.

Regards.
Slava

 

[slavag]

Sorry Scotty. I re-read your last post. You are still have link. It's great. You need only add PLC Modbus slave between two Modbus masters, w/o any logic, only maping of adresses.
Best regards.
Slava

 

[roydm]

Scotty,
No I haven't used one yet but I will certainly be giving it a close look next project. The HMI has the same multi-protocol functionality as the DataStationPlus. Something I like it saves historic data in CSV format and can save very large files whereas RSView saves in some other format that must be translated before you can use it and the files are very small.
Roy

 

[slavag]

Hi Scotty.
We used for this porpuse PLC of ABB--- AC500 ( it's more or less new product on the market with many options of communication).
AC500 have option work with up to 5- TCP/IP adresses.
What we do.
SCS500 is first Modbus master with IP adress and Control system Modbus master with other IP adress. SCS write to PLC Modbus table and control system is read it. Same in other direction. Possible work with one IP adress, but we prefered separate two networks ( SCS and PI).
Best Regards.
Slava

 

[slavag]

Hi.
please find attached

http://www.abb.com/product/seitp329/be2c616b9f2fc3e2c1256ff00047a8f2.aspx

It's CPU with TCP/IP RJ45 port and we added to this additional one, it's all.
Hope that a little help you.
Slava

 

[ScottyUK]

I think we are going to try the Data Station Plus initially, and go for the PLC method as a fallback. The main reason for this is that A-B, who are our preferred PLC vendor, don't seem to make life easy when using ethernet to connect to their PLCs. There's a grey world of third party ethernet Modbus suppliers to fill the gap in A-B's range and I don't have the time to spend on trying to integrate something which will probably fight me every inch of the way.

Thanks for all the help guys - I'll post the result of my trials with the Red Lion product once I have a play with it.


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If we learn from our mistakes I'm getting a great education!

 

[controlsdude]

what about this product if you do not have success?

http://www.inat.de/index.php?id=255&L=1

Looks like siemens liked it between their plc and an AB. Maybe it will work with your ABB?

It supports Modbus TCP/IP.

Its made by Germans so it must work? lol

 

[controlsdude]

forgot about these guys.
I have used there products and they have great tech support.

These are all Modbus TCP/IP gateway devices

http://www.prosoft-technology.com/content/view/full/3255

french office
ProSoft Technology
Zone d'activite de Font Grasse
17, rue des Briquetiers
F-31700 Blagnac

Tel: +33 (0)5 34 36 87 20
Fax: +33 (0)5 61 78 40 52
Email: europe@prosoft-technology.com

 

[roydm]

I second that about product support Controlsdude, I used one of their Modbus PRSMV156-MCM cards, AB PLC to Pneumercator underground storage tank monitor. I called support and they explained to me how to set it up.
It worked first time!!!!!!!!
With 2 unknown products I expected to spin my wheels for at least a couple of days.
Roy

 

[ScottyUK]

Thank you fellas, it is amazing how many of these things are out there once you start looking for them. Regarding Prosoft, it's nice to know someone actually bothers with customer support these days - they'll be next on my list if the Red Lion unit doesn't work out.


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If we learn from our mistakes I'm getting a great education!

 

[slavag]

Hi Scotty.
In additional please see Moxa site

http://www.moxa.com

http://www.moxa.com/product/MGate_MB3180_3280_3480.htm

Regards.
Slava

 

[ScottyUK]

UPDATE!

We bought the Data Station Plus from Red Lion and our subcontractor has sucessfully configured it to bridge between the two Modbus masters. We had to add a router because the two Modbus masters are on different networks but other than that there were no major problems. Thanks for all the ideas.


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If we learn from our mistakes I'm getting a great education!

 

[slavag]

Scotty, thanks a lot for update.

BUT,your:
We had to add a router because the two Modbus masters are on different networks

This is exactly reson: why we choice ABB AS500 PLC. it's Modbus slave with possibility work with separated TCP/IP networks.

Best Regards.
Slava

 

[ScottyUK]

Thanks Slava - it is definitely an option I will consider for the next time. The old SLC500 is our site standard PLC and is the one most of the guys are familiar with, but A-B don't make an ethernet card for it. I know there are a few third party cards available but they were a very unknown quantity which I was reluctant to take a chance with because of the tight timescales. I would have had to contract out the PLC solution if we used a different brand just to save the time spent learning how to program it, whereas I could give the Red Lion unit to Emerson and let them manage the problem for me.

The router isn't a big problem because our network runs through a fairly large Cisco switch which has routing capability so it didn't really cost us anything other than some config time on the switch.


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If we learn from our mistakes I'm getting a great education!