A PLC SCADA or programmable Logic controller-supervisory control and data aquisition is typically the aspect of the system that controls an entire industrial system. These are the control systems that may operate the entire factory, or the waste water treatment plant. Perhaps the words 'control system' is a misnomer of sorts, since the SCADA doesn't really control the processes that are taking place in any given venue, but more supervises and relays information that is necessary to the operator.
Industry requires that we operate plants in ways that can continuously batch process given things. The SCADA permits us to do that with greater ease and without the difficulties that we may have experienced just ten years ago. Some of the processes that the supervisory control and data acquisition may accomplish for us include just monitoring various parts of any given system.
A SCADA system might help you to monitor processes, buildings or facilities or the infrastructure of something. Those processes that it might help you to monitor or run would include generating power, refinery processes such as an oil refinery, production of goods, fabrication of any given item, or even the full manufacturing process and the facility in which it is mad
The PLC SCADA can operate and control how a given item is made or processed. It may do a continuous processing, a repetitious processing, or it may even do just single items, discrete processes. The facility that you would use a SCADA to help you to automate might be anything at all from a public restroom, to a ships hold, to an airport security setup, down to even the space station.
Some other processes that may fall under the auspices of the supervisory control and data acquisition are the processes of an infrastructure. These could include things such as processing that takes place in a treatment plant such as waste water treatment or even freshwater, or reservoir treatment of your drinking water. The kinds of places where you might use the SCADA include not just public works or utilities, but also private industry infrastructures such as oil pipe systems and oil refineries.
In addition to these things, some public services that are operated by a SCADA would probably surprise you. In fact, your weather alert system, tornado and bad weather warnings and even the siren systems for them, as well as the sirens for things such as civil defense may be operated by a SCADA. Your local volunteer volunteer fire system sirens may also be tripped by a supervisory control and data acquisition system. In some fire services, the information comes in by means of a relay and a given system is aroused or a given action takes place such as the siren going off or doors closing and so on. These are good examples of both facilities and systems being operated using PLC's and SCADA..
Typically, a PLC SCADA system will have more than one PLC under its watch and control, with PLCs located at the various individual processing and manufacturing machines.
In every SCADA system, there are several other kinds of smaller or subset of systems that are also used to assist in the processing that the SCADA has to do. The users of the SCADA are offered all of the information that they need to carry out the kind of work they must do by the user of an HMI, or an interface between humans and machines. This is known as the HMI portion of the SCADA.
Essentially, a SCADA doesn't control the system directly. What it does is to oversee and relay information from one place to another, coordinating all of the various things that are taking place with it.
The SCADA acts as a supervisory and very often as a controlling mechanism that tells the humans what is incoming, what is necessary and then relays the information out for them. The PLC SCADA in many cases doesn't even use the master or the main computer. It can offer solutions to the various processes that may not require the main computer using what are called SMART PLC's or another technical component, ladder logic.