PLC and relays
PLC: u can connect I/O to it, can be analogue, digital and others. The program in the PLC that u need to program will do whatever u programmed with the outputs.
When u have a problem, something is not working, u can monitor your program and see what the problem is, an input that's not coming in for example.
PLC can these days control drives and peripheral stations with I/O. U can run a machine on a PLC concept; and when u have a problem or need to change somehting, u just program it on your desk, download it to the CPU from your desk and that's it. U didn't even moved from your desk.
No cables to care of when there needs to be a change in a sequence.
One thing that's less good: It's isn't cheap in the beginning, but...
If it can help optimize your finishing product and can reduce the down-times by this concept, u will win it back in no time.
Relays are good, but what about analogue control, a module for comparision, a module for pid, a module for timer, a module for that, etc... Will also cost, and u will need a stock of reserve modules !!!
Think about it !!
A life with PLC is a wonderfull life (not always
)