Process Control Systems for industrial processes normally come in two
flavors: SCADA/PLC systems and DCS systems.
A SCADA/PLC system consists of a PLC doing the actual plant control,
with the field instrumentation and actuators wired to it, and the
SCADA being the human interface for it.
A DCS has the plant control and human interfacing combined in one
A SCADA/PLC system is "normally" significantly cheaper than a DCS and
for many applications as good if not better than a DCS.
For some applications, like an oil refinery, a DCS is better, and for
these types of applications it is worthwhile to pay more.