In the past couple of years, we've been doing most of our PLC programming work on Unity-Pro.

This is great for object oriented control algortihms & complex problem solving. We're still apprehensive to move on to OPC for the PLC-SCADA linkage and this is because most of our team has been raised on the common Modbus protocol typically over Ethernet/RS-485.

Now that we are using structured/derived variables in the PLC program, I feel that using elementary addressed variables in the SCADA application is a little dated! Now can you people who have experience with OPC or have migrated from I/O servers tell me whether it is worthwhile to make the switch?

With my limited understanding of it, OPC is perhaps just another I/O server, What is so big about OPC that it is progressing to being something of a profession in its own right?