I suggested the PLC approach in my answer to your other question.
Figure 1. A remote I/O (input/output) block. From left to right: network ports, power connector, input / output terminals.
Remote I/O comes in many forms from panel / DIN-rail mount to modular, snap-together, etc. The units are "dumb" in that there is no program in them. They read the status of the input signals and pass them back to the controller on request. They receive output commands from the controller and set the outputs as instructed.
Remote I/O blocks are available for
- Digital signals - typically 24 V DC, 110 or 230 V AC.
- Analog signals - typically 0 to 10 V or 4 to 20 mA.
- Thermocouple and Pt100 temperature sensors.
Some output blocks can switch high currents (maybe 10 A or so) and this may avoid the use of additional relays. Sometimes the replaceable relay is preferred for long-term ease and cost of maintenance.
You might find some suitable software to control the remote I/O directly from a PC. As I suggested in the answer to the other question, keep it simple, scaleable, reliable, long-term vendor support, and, above all, maintainable by someone other than you!
