You can use either a managed or an unmanaged Ethernet switch for PROFINET. Of course, if downtime is expensive for you, you will easily justify using a managed switch. (See past post.) You can use an OPC-SNMP server to read information from a managed switch and display it and alarm it in an HMI. It’s wonderful that the information can be seen in an HMI, but what if you want the controller to take some action as a result of diagnostic information? PROFINET does that.
An Ethernet switch can also be a PROFINET device! The switch will look like IO to the PLC. This means the switch will have a GSD file just like any other PROFINET device. And the GSD file will define what diagnostic information can be read. For example, if a device is unplugged from a switch port, the PLC logic can execute an appropriate action. This is even more valuable if the switch is an MRP device (Media Redundancy Protocol). Here’s a one-minute refresher on redundancy:
If the switch reports a failure in the ring, the PLC can alarm it and act on it. In fact, it can pinpoint where the break in the ring is, simplifying the maintenance response. Many vendors supply Ethernet switches that are also PROFINET IO devices, including Cisco, Siemens, Moxa, Phoenix Contact, Harting, and Hirschmann.
With PROFINET you can use an unmanaged switch, a managed switch, or a switch that is also PROFINET IO. It’s good to have options.