Profinet and Modbus TCP

PLCnext Engineer
1

We are considering a system that would need to run both Profinet and Modbus TCP. on a very small demo (1 station of each) this appears to work, wondering if there are any concerns with “scaling up” to a larger system, say 40 stations of modbus TCP and 20 stations of profinet?

2

Hello, obviously it is possible to scale it up but there are alot of factors to take into consideration:

                                               * Who is the Modbus client/ Server ?
                                               * Who is ProfiNet Control / device in your setup?
                                               * Do you want one PLCNext Controll to be the Modbus Client on 40+ Modbus Servers and the ProfiNet Control of 20 Devices?
                                               * What are your requirements on Polling Interval or PN Update time?
                                               * Which Hardware are you using? 
                                                 * AXC F 1152, AXC F 2152 or RFC 4072S?
                                               * What other aplication is running on the PLC and what are the RealTime requirements there? 
                                                 * Do you have Realtime Requirements?
                                                 * more like 1ms or 1000ms cycle-time

kind regards;
Oliver

3

HI Oliver It’s good to know that it will scale up - a previous company I worked for had a product that would quickly run into problems if you tried to bump it up, due to the way it handled networking communications In the US we are pretty much leading with the 2152. We are wanting to use 1 F2152 for each system. Speed requirements need to be discussed. But I wanted to make sure there was nothing in the internal architecture of the F2152 to make this a bad application The Modbus remote stations are conveyor controllers - about 20 registers The Profinet devices are barcode readers - just a few words

4

Hey, I dont see any issue here 20 Profinet Devices (min. 16ms Update Time) and 40 ModBus client connections should be no issue (if the update time is not to high). There are no artificial restrictions on the amount of connections you are able to open.

The only limiting factor is the OS or the performance of the PLC.

Still 40 Connections can be alot if your polling time is fast…
→ you will have to take a look in detail and properbly do some measurements.

IF the AXF 2152 or AXC F 1152 might not be powerfull enough ->next year we will release the AXC F 3152 which will be even more powerfull. kind regards,
Oliver

5

Hi tthayer and Oliver, I have run some tests with hybrid communication protocols. with 20 profinet devices you can see some issues. Especially if your devices contain analog I/O’s or frequency inverters that transmit larger amounts of data. I have seen the freez of values from inverters (motor current, motor speed) from the invertes. That combined with the ModBus communication (Modbus TCP) with some engery meters (10) really put the strain on the AXC F2152. In fact, the controller got really hot - fast. As Oliver has mentioned, the AXC F3152 is coming the next year, and I would think that it is the better option for you. With your planned setup, you are on the limit and have no room to manuver in. Run some tests with the AXC F2152 for the final project use the AXC F3152. I have been there. Did try to save on the controller, only to spent more on fixing the issues later. Sadlly, the theory what a controller can and the real world applications don’t always work. Test, Test, Test! Better spend some time testing before you implement it at a client.