Basic PLC operation

Plc logic controllers can be simple and to what extent? We have a common household space heater.
Heater member sealed in a container, ease of system communications. This concept can be extended to a remote control home thermostat heater, communication distance of a few meters, usually voltage control.
Now, we are in this small, simple process control system to be expanded on the basis of which the control and configure a plant need?
Long-distance transmission line impedance, EMI and RFI voltage control scheme makes implementation very difficult, in this case, the current loop is a simple and effective solution. Kirchhoff's law by the current loop current loop at any point is equal to all other points in the current, which can offset the impact of the transmission line impedance. Because the loop impedance and bandwidth (a few hundred ohms and "100Hz), EMI and RFI spurious pickup issues are minimized. digital output plc system is useful for properly controlling such a factory production system.