Profibus - Modbus TCP translator

ewm3

Member
Join Date
Oct 2003
Posts
1
I am looking for a converter/translator that will convert Profibus to Modbus TCP. Specifically, I need to read data from several Siemens PLCs (which are networked together via Profibus), and all I have is a Modbus driver (it can read data via Modbus serial OR Modbus TCP - Ethernet). I assume this is some type of protocol converter. Also, I am NOT allowed to touch the existing Siemens PLCs; the converter has to stand alone (the Siemens PLC programs can NOT be touched). So, this device would poll the PLCs via Profibus and make the data available in a Modbus TCP server. Any ideas?
 
ewm3 said:
(the Siemens PLC programs can NOT be touched).

You stated that the Siemens PLC's are networked together via profibus and I take it that they are passing data to each other via a CP card in each PLC?

So, I am not sure how you are going to poll the PLC's without editing the existing programs, because when data is sent to another PLC that data has to be specified, I would be very surprised to learn that you could just walk up to a PLC and say 'I want this data or that data' and expect it to give it to you if you haven't already 'told' it that you will be asking for it :confused:

Paul
 
Hello!
The answer to your problem is IMPOSSIBLE to do that !
Suggest you buy a Profibus card+driver to your server and then you can
"ask" the PLC:s for the information without changing the S7 programs!
This will save you a lot of troubles.
If you want to use Modbus you have to buy one card/plc +expensive drivers and program the plc:s and server. (one way is one card+driver and transfer all data to that plc by profibus)
 
I've actually commissioned links like you describe a few times using a variety of products. Initially we used SST X-Link because it has a strong Profibus DP driver, but the Modicon TCP/IP driver is problematic. Lately we've used Liaison S3 (www.liaisontech.com) with gratifying results. Its Modicon TCP/IP driver is very robust and recovers well from broadcast storms and other anomalies we introduce as part of our validation process (It uses an SST interface for Profibus DP communication).

The profibus master interface is set up with a scan list of the active stations and the data read from card memory into an internal database. From there is can be aliased to a modbus registers by data type and read and written asynchronously. The unit provides a diagnostic and monitoring facility through the IE browser which allows a user to see the data as it appears in the database. It has huge resources, allowing the interface of several fully loaded Profibus networks to Modicon or other Ethernet drivers (usually AB CSP --PLC5e-- ethernet and Controllogix Ethernet).

Its perfect for situations like you describe where previously validated PLCs have to be left alone. The unit is small and DIN rail mounted.
 

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