Choosing a network (MPI,PROFIBUS,ethernet)


Thread Starter


Hi, i have a question about choosing a good network for my project..which is reading PLC data from Siemens S7-400 PLC's.

The PLC structure which our company uses is the following:..

there are several machines which are controlled by a master PLC (S7-400) each machine has 3 units which are controlled by a S7-300 PLC and are connected to the master PLC by a MPI network.
The S7-400 master PLC has also 11 components connected by profibus and each unit(S7-300) has +/- 5 profibus components attached.

the problem is as following: I have to choose a network type where i can collect data from the several master S7-400 PLC's by a OPC server.
my question to u is, do i have to buy CP443-1 ethernet modules and connect the masters by ethernet or is there any kind of switch which is capable of connecting several MPI networks or Profibus networks? and what is the best sollution.

i hope that u can help me.

thanks in advance

Daniel Chartier

Hello Mr. Schraa;
Nice little problem.
You can of course use Industrial Ethernet to connect the S7-400 CPUs, as you suggest; it will work well, and you can connect through OPC--you will find the OPC drivers for I.Ethernet on the SimaticNet CD. It is an expensive solution though; you would need 3 CP443-1, a switch and a CP1613 + I.E driver on the PC.

You can also use MPI to connect the S7-400 CPUs and connect to the MPI network through a CP5613 comm. processor on your PC (no supplemental driver required for MPI). Use Profibus cables and connectors to connect the CPUs. Siemens has a support entry # 6917179 on their website on connecting to MPI via OPC:

This solution will work if all processors are included in a single project; that is, all programs must be part of the same project, and all network connections must be reorganized and renumbered (with Netpro)so the OPC client can access all CPUs correctly, wihout confusion. Since the network is limited to 187,5 kB, your performance will be slower than with I.Ethernet; evaluate how much data you expect to transmit through OPC before you decide.
Hope this helps,
Daniel Chartier
I'm collecting data from the several S7-400 MASTER PLC's into a PC (server) the logged data will be stored in a database. In the beginning there will only data logged which contain a count of produced items and the different failures that have occured during production. in the future there will be more data logged and also data send to the PLC.
I found out that there are 2 options for communicating via ethernet. option 1 is buying a CP443 ethernet module for the S7-400 which is very expensive.
option 2 is buying a netlink module which converts MPI to ethernet. example :

the difference is that the netlink speed with the S7-400 cpu is max 12Mbit/s and with the CP443 can the speed reach up to 100Mbit/s.

If i go for this netlink wil this have effect on my PLC cycle time because i'm communicating via MPI?

hehe a lot of questions here :)

thanx in advance
Well it seems to me that you could do this with a profibus card in the PC with the database. The PLCs should all talk profibus FMS. Depends on whether the PC is physically located near the profibus bus and whether you are comfortable writing some code. You can get a profibus card from SST or Siemens or others and I think they have automation interfaces that can allow you to use them in VB. If not I know the SST cards come with free OPC servers and you can download an automation proxy dll for OPC DA from the OPC web site which will allow easy VB access. Writing and testing code is never as easy as you think but this could be one approach.