Siemens S7 and Modbus Plus network

Hi All

I have followed this great site for many years and have now found myself in the need of greater wisdom from the PLC community...so here goes.

I have a site that is currently quite old with conveyors and storage retrieval machines. They all currently run on old Modicon and Micro PLC's. We are looking to upgrade the SRM's which would involve using an S7 PLC new AC inverters etc etc. Something we have done many times before. The catch comes with the existing set up. The host system (customers) talks to a PC on a socket connection over TCP/IP. This PC (its quite old) has a bespoke piece of software running that takes the host message and sends out onto the Modbus Plus network via an SA85 card. There is no support for this PC. Our aim was to put an comms concentrator between the Host and the PC (PLC based)and peel off the SRM messages and send over a new Ethernet network and pass the conveyor ones directly onto the old PC which would now have a socket conection to the concentrator. This all seems viable and should the conveyors be upgraded in the future they can be put onto TCP/IP and remove the old PC altogether. However the customer has become so nervous that should this PC fail they are stuck up a creak....therefore they want to see if there is something we can do going forward.

The options that I see are either connect directly to the comms concentrator PLC (which would be siemens as its our standard) or look at some sort of network gateway.

Having very little exposure to Modbus Plus and spending a fair while surfing I was wondering if anyone has come across this sort of thing before.

In a word - No!

I recently was involved in programming an S7300 plc as a Modbus Master (You can be a slave to). You need a comms card for the plc, and a dongle, which must retail at close to £900 by now!

I am not sure about modbus plus bit but what I did called the relavent slave and allowed the returning data (Temperature and vibration levels) to be "Read" in a standard data block. From there I could do some comparisons with set levels and display them on an HMI.

Siemens provide some sample programs which I used as the basis for my program. I found the addressing of the Modbus slaves different to what the manufacturer said but it all worked in the end!

Hi,

To be quite honest, I do not quite understand your setup and what the goal is. Still, I know some about Modbus+ and Siemens.
You may want to have a look at a gateway solution, going from Profibus to Modbus+....
http://www.anybus.com/support/support.asp?PID=186&ProdType=Anybus X-gateway

If you would like to talk about it, drop me an email at:
[email protected]

Patrick Lansdorf

Gentlemen,

The Modbus and Modbus Plus are entirely different protocols.
Is like (in Siemens terms) you're talking about Profibus DP and Profinet.
If you have a system using MB+ and you want to integrate Siemens, the best options are:
1st. Verify if the system allow any Siemens standard protocols, like ProfibusDP
2nd. Going with a protocol converter (BM85S Programmable Modbus Plus Bridge/MUX)
3rd. Bridging it with a PC running a OPC...

Regards,
MifPT