What is SCADA?
Supervisory Control and Data Acquisition (SCADA) is an acronym that typically refers to the highest level in a hierarchy of Industrial Control Systems (ICS) that in turn manage the automation of large and complex processes. The process data are presented on a computer screen to operators at a central command center where they monitor and control the process at the supervisory level. Real time automation and control of the process is performed by electronic control equipment located remotely near the process equipment. Computers at the central command center communicate with those at the remote locations. The acronym is applied both as an umbrella for an entire system and to the specific software that implements the supervisory control capability.
SCADA is found in utilities such as natural gas, petroleum, water treatment and the electric power transmission where the controlling equipment is located in stations distributed over a large geographic area. The SCADA acronym is sometimes applied in non-utility processes such as chemical and pharmaceutical manufacturing, food processing, building management systems, and heating ventilation & air conditioning (HVAC). In practice, SCADA, Industrial Control System and Instrumentation & Control System (I&C) terms are sometimes used interchangeably.
The typical SCADA system consists three main elements:
- A central command center housing computer servers running SCADA software.
- A number of remotely located local control systems or devices which interact directly to control and automate the process equipment.
- A communication system, telecommunication or internal network, that connects the computers at the central command center to those at the remote locations.
An example is the Northern California natural gas transmission system. About 6000 miles of pipeline that is outfitted with approximately 9000 sensors, valves, pumps and local control stations. This system is managed from a central location by operators sitting in front of sophisticated computer stations. The operators can manage the flow and storage of gas, transfer of custody of gas is it bought and sold to other companies, and monitor the condition of the system. They dispatch maintenance personnel or alert emergency response services when needed. The SCADA software that has been configured for their system resides on a bank of computer servers. Actual automation and control of pressure or flow in the pipelines, is accomplished at local control stations and by remote equipment mounted along the pipelines.
SCADA is also found in manufacturing. An example is the production and distribution of sterile water in a pharmaceutical plant. A SCADA system can be used to supervise the stills, distribution piping, and pumps, while monitoring the associated instruments. Another example could be the management of an automobile assembly line. The operators could manage the scheduling, sequencing of all the robotic equipment, delivery of components to the line from a central location. At the actual line level, many locally controlled robots operate independently on command from the SCADA system. In practice, different acronyms are used inside a company to refer to these technologies.
What is ICS or I&C?
Industrial Control Systems (ICS) are computer controlled systems that monitor and control industrial processes that exist in the physical world. Instrumentation & Control (I&C) is the similar term that was historically applied in chemical, pharmaceutical and petroleum industries before computers came into general use. Historically, automation of manufacturing and process equipment was accomplished with mechanical, pneumatic and hydraulic systems. Today, automation is universally accomplished with specialized computers that can communicate with real world electronic instrumentation and mechanical devices.
What is a PLC or RTU?
An ICS typically consists of the specialized computer called Programmable Logic Controller (PLC) which connects directly to instruments, valve actuators, pump motors, robotic machine actuators, and whatever equipment is needed to implement some process. In turn the PLC communicates over a network and telecommunications lines with other PLCs, graphic operator interface panels, and with a SCADA central command center. PLCs are programmed in a specialized language that mimics relay logic and also provides automated control functions to manage pressure, flow, temperature, motion control, and all process variables. Historically, automated control functions were accomplished with discrete controls, either mechanical, pneumatic or electronic. Today, most of that functionality is accomplished in the PLC with software.
A Remote Terminal Unit (RTU) is a device, that is not unlike a PLC, which provides the interface between an item of equipment and the SCADA system. While a PLC is multipurpose and programmable and expandable, the RTU typically is designed for a specific narrow purpose and lacks programmability.