A control system architecture called SCADA (supervisory control and data acquisition) uses computers, networked data communications, and graphical user interfaces to provide high-level supervision of devices and processes. It also includes sensors and other equipment that connect to machinery or process plants, including programmable logic controllers. A set of hardware and software components called SCADA (supervisory control and data acquisition) enables factories to: 

• Organize and manage industrial operations locally or remotely  
• Real-time data monitoring, gathering, and processing 
• Using human-machine interface (HMI) software, you may directly communicate with equipment like sensors, valves, pumps, motors, & more. 
• logging events in a file 

Industrial companies use SCADA systems as they process data, allowing the company to make more informed decisions, continue operating efficiently, and be notified of any problems that may arise, hence reducing the amount of time spent offline. 

PLCs or RTUs – remote terminal units are the first components of the fundamental SCADA system. PLCs and RTUs are small computers that interface with a variety of devices, including factory equipment, HMIs, sensors, & end devices. 

After that, the SCADA software on these computers will transmit the data coming from these things to the computers of other organizations. 

Operators and other staff members can use the SCADA software to process, distribute, and display data in order to analyse it and make crucial selections.

Components of SCADA

1). HMI, or human-machine interface 

It’s an input-output device typically displays the process data for a human operator to control. It is used to provide management information, such as planned maintenance procedures, intricate schematics, logistical data, trends, and diagnostic data for a particular sensor or machine, by connecting to the SCADA system’s software programs and databases. The operations staff can view the information graphically because of HMI systems.

2). Supervisory System

The SCADA system’s equipment, such as RTUs, PLCs, & sensors, etc., & the HMI software utilized in the control room workstations, serve as a server for communication. 

• In smaller SCADA systems, the master station, also known as the supervisory station, is a single PC. 
• In bigger SCADA systems, the supervisory system includes distributed software programs, disaster recovery locations, and several servers. 

These several servers are set up in a hot-standby or dual-redundant configuration, which continually monitors and controls in the event of a server failure to increase the system’s integrity. 

3). Remote Terminal Units

The Remote Terminal Units (RTUs), which are microprocessor-controlled electronic devices, connect with the physical objects in SCADA systems. These units are used to communicate messages from the master system to control linked items and to relay telemetry data to the supervisory system. They are also known as remote telemetry units for this reason. 

4). Programmable Logic Controllers 

PLCs are linked to the sensors in SCADA systems in order to gather the sensor output signals and transform them into digital data. PLCs are utilized in place of RTUs due to their benefits over RTUs, such as flexibility, configuration, versatility, and affordability. 

5). Communication Infrastructure

For SCADA systems, radio and direct cable connections are typically employed, however SONET/SDH is frequently used for major systems like power plants and railroads. A few communication protocols that are standardized and accepted by SCADA vendors are among the very minimal SCADA protocols utilized in SCADA systems. 

These communication protocols give information only if the supervisory station polls the RTUs. SCADA programming, sixth in a master or HMI, SCADA programming is used to create maps and diagrams that provide critical situational information if there is a of an event failure (or) process failure. The majority of commercial SCADA systems are programmed using standard interfaces. Programming for SCADA can be done in C (or) derivative programming languages.

MTU or Master Terminal Unit 

A controller that also serves as a server, hosting the control software that interacts with lower-level control devices like 

• Programmable Logic Controllers (PLCs) and 
• Remote Terminal Units (RTUs) across 
• An ICS networks. 

This is frequently referred to as a SCADA server, MTU, or supervisory controller in a SCADA system.

The Programmable Logic Controller (PLC), dedicated computer, or network server that communicates with distant field side RTUs serves as the SCADA system’s intelligence. It starts all communication, gathers data, stores it in a database, gives operators interfaces, and then sends the data to other systems.

Depending on the data gathered, it enables users to execute controlling activities on field devices like breakers, switches, and other actuators. In order to simplify 

• Data logging, 
• Alarm processing, 
• Trending and reporting, 
• Graphical interface, and 
• Security system, 

it is constantly in communication with other devices in the master station.

RTUs or remote Terminal Units 

By transmitting telemetry data to a master system and using information from the master supervisory system to the control connected objects, a remote terminal unit (RTU) connects physical objects in the real world to a distributed control system (DCS) or SCADA (supervisory control and data acquisition) system. 

• RTU can also be referred to as a remote telemetry unit or a remote telecontrol unit.
• RTUs collect data from several of the field sites where they are utilized. Different actuators and sensors that control nearby process (or) field equipment are connected to each RTU.
• It gathers data from a variety of sensors and transmits it to the MTU. Additionally, it receives control instructions from MTU and responds by controlling numerous actuators.

Many RTUs keep the data in their database & wait for the MTU to send (or) transmit a request before sending or transmitting the data. In complex systems, PLCs are employed as RTUs, which transmit field data directly and control settings without the MTU’s intervention. It communicates with numerous field intelligent devices through a local area network.

Human Machine Interface 

The human-machine interface is used by the SCADA system. The data is monitored and displayed for human processing. Access to numerous control units, including PLCs and RTUs, is provided by HMI. The system’s graphical display is provided by the HMI. 

Ex: It gives a graphic representation of the tank’s attached pump. The user can observe both the water’s pressure and flow. An alarm system which is activated based on specified values is the key component of the HMI.

SCADA Functions

1). Data Acquisition

MTU manages the routine collection of data through RTUs in SCADA systems. The RTU can respond to changes in the status of a parameter or when the parameter’s limits are exceeded without receiving a request from the MTU by sending a request to the MTU or by sending data continually.

The RTU internal database is internally scanned as part of the data collection process, as is periodic RTU polling by the MTU, data transfer from the RTU to the MTU, data scaling into engineering units, and updating a prior value (or) state in the database.

2). Human Machine Interface (HMI)

SCADA options integrate text and synoptic graphics to convey the data across several screens. It provides the option for human operators to constantly monitor the processes and to take appropriate action as needed.

The SCADA HMI software is made up of a library of graphical symbols, each of which has a tag name attached with it for a specific device or parameter (such as the ON/OFF status of a switch or the level of a tank, for example).

The majority of the HMI’s display selection options are arranged in a tree structure, with index pages that let a human operator choose from a variety of displays by utilizing a trackball, keyboard, cursor, or touch-screen positioning methods.

3). Supervisory Control

It is the action of managing equipment operations from a distance. In SCADA systems, the MTU at the master station transmits control instructions to the RTU at the remote station, including set points & discrete control commands. RTU receives the commands at the distant stations and controls an appropriate actuator in accordance.

Selecting the remote station, deciding which equipment needs to be managed, and carrying out the required command, such as close or trip, are all included in the supervisory control. The majority of systems use the “check-before-operate” strategy to ensure that the equipment is chosen and used properly in remote locations.

4). Trending

The trending features offered by all SCADA programs show the collected (real-time) (or) saved (historian) data on different charts. The criteria that will be trended on a particular chart can be predefined or defined online. These graphs can use one or more plots to illustrate one or more parameters. It offers data automated scrolling and improved zoom features. With older databases, historian trending is conceivable.

5). Processing Alarms

It entails providing the location, time, device ID, & nature of the event in order to notify the operator of unexpected happenings.

By evaluating the received data with the proper limitations, the master control station logically programs alarms. Alarms can be handled at various priority levels. Alarms can be silenced either individually or collectively.

6). Information Reporting and Storage

The acquired data is kept by SCADA on disks or other long-term storage systems. Data is logged on a cyclic basis, therefore the length of a rotating chronological file (which may be 40 days or 12 months) is constrained.

When the time period is over or the log is full, the data is archived to a permanent storage medium, and any data that is longer than the file time period is subsequently deleted. This makes it possible for the user to access and examine the data whenever necessary.

The report creation offered by SCADA uses SQL-style queries. The historical file serves as the information source for creating different reports. SCADA makes it possible to print and store reports as well.

SCADA system Characteristics

Since some SCADA systems may have unique functionality for particular businesses or uses, the majority of systems provide the following features:

• The basis of SCADA systems is data collection; sensors gather data and transmit it to field controllers, that in turn transmit it to the SCADA computers. 
• On the basis of the information gathered from field sensors, field actuators are controlled remotely.
• All SCADA operations are made possible by networked data communication. Sensor data must be transferred to SCADA field controllers, which in turn connect with SCADA supervisory computers. The SCADA supervisory computers then provide remote control instructions back to actuators. 
• HMIs are used for data presentation, displaying both recent and older data to the SCADA system’s operators. 
• Both historical and current data are crucial components of the SCADA system because they let users compare present performance to past trends. 
• Alarms notify SCADA operators of potentially important system situations. Alerts can be set up to warn operators when certain SCADA operations need to be stopped, started, or altered, when they are blocked, when a system is failing, or when other conditions arise. 
• Report on SCADA system operations may comprise system status reports, process performance reports, and reports tailored specifically for a given use.

Significance of SCADA

• Increased equipment lifespan due to rapid system performance knowledge. 
• Reduced labour costs for service or troubleshooting. 
• Automated report creation increases compliance with regulatory agencies.
• No need for an extensive capital expenditure. 
• For access to real-time data presentation, warning, trending,  & reporting from remote equipment, many automation firms use SCADA. 
• It provides the freedom to select machinery and systems based on functionality rather than compatibility with existing infrastructure.

SCADA Applications 

The flexibility, dependability, & adaptability of SCADA have led to its widespread usage in automating complicated systems. 

SCADA has proven to be effective in providing control and monitoring solutions across a wide range of industries, from power generation to agricultural systems, in a number of real-world applications. 

Below are a few of these applications. 

• Manufacturing facilities or industries: A SCADA facilitates in the synchronized control of automated systems and the management of various inventory items (or) raw materials.  
• Telecom and IT-based systems: The SCADA makes it simple to manage various RF-based systems, communication mediums, and massive communication systems, providing data logging through antennas. 
• Water and sewage treatment facilities and supply management: The state or local corporation uses SCADA-based systems to track, manage, and control water capacities in reservoirs. 
• Controls over traffic: SCADA aids in the regulation of traffic signals, manages the flow of traffic in railway systems on roads, and regulates air traffic. 
• Lift & Elevator controls: Controls for elevators and lifts can also be implemented using SCADA.
• Structures, settings, and environments: SCADA is used by facility managers to regulate HVAC, refrigeration equipment, lighting, and entry systems. 
• Waste Water Treatment: Filtering the raw water either from the wells or the surface and releasing the clean water to the distribution system are both parts of the waste water treatment process. Low lift or raw water station, pre-treatment, filtration, high lift or treated water station, and chemical injection systems are among the processing sections in the water treatment process. 
• System for Distributing Electricity: With the utilization of intelligent electronic devices (IEDs), such as RTUs, the SCADA system automates the duties associated with electrical distribution. SCADA monitors the whole distribution network to ensure optimal performance and a reduction in outages’ duration. Substation control, feeder control, and end user load control are SCADA functions in the electricity distribution system.
• Power Generation Facilities: In thermal power plants, different equipment is dispersed throughout the plant and is all connected by SCADA systems. Numerous boilers, turbines, and pumps can be monitored and controlled due to the SCADA system.
• Plant Function: The plant’s functions, such as coal pulverization, steam flow control, turbine start/stop status, water control into the boiler, and power distribution and control, are automated and monitored by SCADA. 
• Industrial Management :SCADA is frequently used in a wide range of industrial applications, including manufacturing (steel plants), process, oil and gas, food processing, & so forth.
• CCS- Central Controlling Station: The incorporation of SCADA into industrial processes leads to higher production rates, improved product quality, and efficient operations. PLCs are crucial in these industries for handling field parameters and transferring them to the CCS- central controlling station.