A SCADA system is a centralized system that is used to monitor, regulate, and gather real time data from possibly remote locations. A SCADA system will also interact directly with devices such as sensors, motors, and valves. The sensors, motors, and valves are attached to processed such as distribution of water, traffic lights, electricity transmissions, gas transportation and oil pipelines, which could have very devastating consequences such as loss of life or the crashing of economics if these processes were to fail. The SCADA system will read the output of the sensors, motors, and valves and give a reading back to the HMI or a human machine interface. The human machine interface is a local computer that gives the data from the SCADA system to the human behind the operation. The only form that the human machine interface will give its data is in graph form, and it will do so in real time. A SCADA system is in place to try and mitigate critical infrastructure systems.
Critical infrastructure systems include but are not limited to, malware attacks, DDos attacks, and natural disasters that cannot be foreseen. For example, devices such as sensors, motors, and valves could be hacked and switched to cause mass damage, but SCADA systems will use a basic system call an air gap. An air gap is a disconnected network from the internet to try and mitigate the risk of having the malware attacks and DDos attacks come through the internet. SCADA systems also have state of the art industrial VPS and firewalls for the networks. SCADA systems are secured physically as well so there can be no internal attacks.
Not a lot of people know about SCADA systems and their critical roles in everyday life. These systems need to be checked and updated regularly to prevent a huge disaster from occurring.

http://www.scadasystems.net
https://www.dpstele.com/scada/how-systems-work.php