arekk said:
I asked this question because my boss claims that ethernet is the fastest net and the most relible and so on and he isn't satisfied with our net He would like to all PLC's connected via ethernet. Our PLC's are connected via controlnet but we have 4 ethernet gateways. It is hard to argue with your own boss
Okay, that helps.
For I/O, and devices, it's still very hard to beat ControlNet, even though it is technically a 5 mbps network. If you are loading it down on a single machine so drastically, that you can't keep your RPI below 20 msec or so, you can always another ControNet card. For example, even though it isn't needed, I usually use one ControlNet card for all I/O to slave racks, and a second one dedicated only to Drives.
For supervisory access (remote monitoring and programming, or HMI's) I stick to Ethernet. Also, in some very limited cases, where I have no choice (such as inter-PLC communications), I'll MSG over Ethernet, but it isn't my choice, and I don't do that for critical applications.
For the same I/O count, the speed of either will be similar, even if Ethernet is running at 100mbps, as the CPU still has to deal with everything coming into it, and will be scan-time limited. One big drawback for Ethernet, it it is relatively easy to crash, if you have a network that people can add/remove/modify devices without careful supervision. Another, is there is a tendancy to use extremely sub-par Ethernet cables, switches, and routers, because they are so cheap. The local office supply store's Ethernet switch is NOT A GOOD CHOICE in an industrial enviornment.
Once you start moving to proper, hardened, managed switches, and high quality patch panels, the Ethernet cost goes up drastically.
I also hate the idea of the IT department messing with my control networks. ControlNet prevents that.