What Is The Difference Between Siemens PCS7 and Siemens SCADA?

Lesson #1 when I went to Siemens training on PCS7... A DCS system makes "stuff", a PLC makes "things". It's not really that simple and the lines are blurred, but that's a good starting place.

PCS7 is a Distributed Control System, a collection of smaller process controllers or process loops running in a computer working together in a coordinated manner to achieve an overall goal of making products in which each individual process is part of the larger process. So a chemical factory or a refinery would use a DCS to run the entire plant, or they may use a DCS for each individual portion of the plant that is making a specific product. PCS7 is just Siemens version of a DCS. Any DCS must have local hardware that takes in the I/O information from the processes. In the case of the PCS7, the hardware they use is the same hardware used by their S7-400 PLCs, but the controllers and software is very different.

SCADA means Supervisory Control and Data Acquisition. So it CAN be a lot of different smaller controllers, such as PLCs running their own software, but each part of the system is not necessarily an integral component of the larger system in that if all communication is lost, they still function on their own. However the larger system must keep track of everything that is taking place because not only must bigger decisions be made, but advanced warnings of external changes will indirectly affect other parts of the system. An example of a SCADA system would be a waste water system in which you have a water treatment facility (which may have a DCS running it) and a spread out system of individual pump stations all across a district that are feeding to it. The pump stations can all work on their own for the individual local needs, but the SCADA system must watch them at all times to know what is happening. So the SCADA system can be made up of many different types of controllers, but there is an overall PC running software that is "supervising and collecting data" from all of them.