PROFINET on Unmanged Switch & 50 Mbps Regular Antenna

nicer

Member
Join Date
May 2011
Location
manila
Posts
32
Good day experts!

I'm working on a Profinet system which passes through unmanaged switches and a 50 Mbps antennas (please see attached file for the system architecture).

Now I'm having a communication error to both gateways (diagnosed through online HWConfig) even though I can ping and find on Simatic Managers' "search ethernet node" all the devices from all different switches and even upload and download to the CPU315. This might mean that the ethernet network per se is fine, but maybe not good enough for Profinet protocol.

I've tested my configuration on bench (direct CPU-gateway-power meters connection) so my suspicion lies outside, on the netwrok, namely either or both the switch and antenna (and someone told me that the switch recommended on Profinet systems are the "managed" ones and that Profinet system has a minimum requirement of 100 Mbps, but the antenna only has 50 Mbps capacity).

So I made some isolation. First I pull the gateway and connect it directly to the CPU once more, thereby bypassing both antenna and switch, and there's no problem. Second, I connect the gateway to the switch, thereby bypassing only the antenna, and there's also no problem.

1) Does establishing communication between CPU and gateway on a single switch (Isolation 2) really vindicates the use of the said unmanaged switch on Profinet system? Because someone told me that maybe that can be fine with only two devices talking on an unmanaged switch, but not when you have four switches and 9 devices (CPU, gateways and antenna, my whole system).

2) If the answer to 1 is "yes", then the problem must be on the antenna, right? Is it due to it being only 50 Mbps? Does replacing it with one of 100 Mbps or more would do the job?

3) We are thinking to bypass only the switch by directly connecting the CPU to it's antenna (it's a POE line, is it ok) and the gateway to it's own antenna on the other side. If this worked, then it must be the switches right? Or is it even worth a try with a 50 Mbps one?

Thanks for any response!
 
What is the cyclic update rate you are running the connections to the HMS Field bus Communicators at ?

What you are describing is a system that doesn't have enough bandwidth for the traffic you are putting on the network. The usual solution is to reduce the amount of traffic by slowing down the data exchange.

HMS Fieldbus Communicators generally poll a serial device, so they don't have to run at 1 or 2 millisecond update times, but more commonly 100 or 200 millisecond update times.
 
I think the Anybus PN IO devices are not HMI devices. They are actually PN IO Devices controlled by the 315 CPU as PN IO Controller.
A Profinet IO System update typically within 2-10 ms, so that is a big difference to 100 ms that a HMI would poll data.

Pofinet RT (not IRT) runs OK with regular wired switches as long as they support QoS.
I am not an expert in PN over Wifi, but as far as I know you need dedicated Profinet WiFi gear to do that.
If it is just HMI comms, then it will work OK, if only there are not too many tags or too fast update rate, but if it is PN IO data then it is totally different situation.
 

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