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SCADA (Supervisory Control and Data Acquisition) systems are used in monitoring and control of industrial equipment in various stages such as development, manufacturing, production and fabrication. This post will discuss SCADA system, basic components (in detail), hardware & software architecture, types, applications, advantages and disadvantages.

Introduction to SCADA System

There are several processes that run in large industrial establishments. These processes are complex to monitor because every machine differs in its output capacities. The Supervisory Control and Data Acquisition system helps in managing this complex industrial procedure by maintaining efficiency, encouraging smarter decisions through data processing techniques and communication of system issues to mitigate downtime.

Fig. 1 – Introduction to SCADA System

SCADA is a system of hardware and software elements that facilitate process control. This central control system consist of communication equipment, network interfaces, input/ output devices and software. It allows organizations to carry out following functions:

  • Manage industrial processes remotely or locally.
  • Real-time data gathering, monitoring and processing.
  • Direct interaction with devices like valves, motors, pumps, valves using Human Machine Interface (HMI) software.
  • Create a log file of events.

This system is used for monitoring and control of industrial equipment in development, manufacturing, production and fabrication phases. Real time monitoring can be achieved through Programmable Logic Controllers (PLCs) and circuit breakers.

Basic Components of SCADA System

A basic SCADA system consists of following components:

  1. Human Machine Interface
  2. Supervisory System
  3. Remote Terminal Units
  4. Programmable Logic Controllers (PLCs)
  5. Communication Infrastructure
  6. SCADA Programming

Fig. 2 – Components of SCADA System

1. Human Machine Interface

It is an I/O device that allows a human operator to control the process data. This is achieved by linking SCADA’s databases and software programs for providing management information like detailed schematics, scheduled maintenance, data diagnostics and logistic information. The operating personnel can also see the graphical representation of data.

Fig. 3 – Human Machine Interface in SCADA

2. Supervisory System

This system acts as a communication server between the HMI software in control room workstations and its equipment like PLCs, RTUs, sensors etc.

Smaller Supervisory Control and Data Acquisition systems have only a single PC that serves as a supervisory or master system. Larger Supervisory Control and Data Acquisition systems have multiple servers, sites for disaster recovery and distributed software applications. The servers are configured as dual-redundant or hot-standby formation for continuously monitoring server failure.

3. Remote Terminal Units

This system contains physical objects that are interfaced with Remote Terminal Units (RTUs). These electronic devices are controlled by microprocessors and are used for transmitting recorded data to the supervisory systems. They also receive data from the master system in order to control the connected objects.

They are also called as Remote Telemetry Units.

4. Programmable Logic Controllers

PLCs find their use in the Supervisory Control and Data Acquisition system through sensors. They are attached to the sensors in order to convert the sensor output signal into digital data.

They are preferred over RTUs because of their configuration, flexibility, affordability and versatility.

5. Communication Infrastructure

Generally, a combination of direct wired connection and radio is used in Supervisory Control and Data Acquisition systems. However, SDH/ SONET can also be used for larger systems like railways and power stations.

Among the compact SCADA protocols, few recognized and standardized protocols deliver information only when the RTUs are polled by the supervisory station.

6. SCADA Programming

SCADA programming in HMI or master station is used for creating diagrams and maps that provide vital information during process or event failure. Most of the commercial Supervisory Control and Data Acquisition systems use standardized interfaces in programming.

C language or derived programming language is generally used for such programming.

Architecture of SCADA

Most often, this system consists of the following components: operating equipment, local processors, instruments, PLCs, RTUs, master terminal, intelligent electronic devices and a PC with HMI. However, for ease of understanding, SCADA architecture may be divided in two categories:

  • Hardware Architecture
  • Software Architecture

Hardware Architecture

The Hardware architecture of this system is classified into two parts:

  • Client Layer: For man machine interface
  • Data Server Layer: For data processing

The SCADA station consist of only a single PC. The devices and data servers communicate with each other through RTUs or PLCs. The PLCs are either directly connected to the data servers or through buses and networks. This system uses LAN and WAN for communicating between devices and the master station.

Fig. 4 – SCADA Hardware Architecture

Sensors are connected to the PLCs or RTUs that convert sensor signals into digital data. This data is then sent to the master unit for getting appropriate feedback. Upon receiving feedback, the RTUs apply the electrical signals to relays.

Software Architecture

Servers are used mainly for real time database and multitasking and are responsible for handling and gathering of data.

Fig. 5 – SCADA Software Architecture

The software architecture of this system consists of programs that provide trending, diagnostic information. Programs also help in managing information like logistic information, maintenance schedules, detailed schematics of a specific machine or sensor and troubleshooting guides.

Types of SCADA System

There are four different types of SCADA systems from four generations. They are:

  1. Early or Monolithic SCADA Systems (First Generation)
  2. Distributed SCADA Systems (Second Generation)
  3. Networked SCADA Systems (Third Generation)
  4. IoT SCADA Systems (Fourth Generation)

1. Early or Monolithic SCADA Systems (First Generation)

Minicomputers were used in the earlier Supervisory Control and Data Acquisition systems. Monolithic systems were developed during times when ordinary network services were unavailable. These were designed to be independent systems without any connection to other systems.

Fig. 6 – Monolithic SCADA System

Back up mainframe was used to gather data from all remote terminal units. Functions of these early systems were limited to flagging of operations in case of emergency and monitoring the sensors.

2. Distributed SCADA Systems (Second Generation)

Here, the control function was distributed across several systems that were connected using LAN. Command processing and real-time data were shared to perform control operations.

Fig. 7 – Distributed SCADA Systems

The second generation resulted in the reduction of size and cost of each station but there were no standardized network protocols. Since the protocols were proprietary, very few people understood the security of Supervisory Control and Data Acquisition system installation and this factor was largely ignored.

3. Networked SCADA Systems (Third Generation)

Present Supervisory Control and Data Acquisition systems are networked and communicate over WAN system through phone or data lines. Fiber optic connections or Ethernet is used for data transmission between the nodes.

Fig. 8 – Network SCADA System

These systems use PLC for adjusting and monitoring the flagging operations only when there is a requirement for major decisions.

4. Internet of Things SCADA Systems (Fourth Generation)

The fourth generation is seeing a reduction in infrastructural cost of these systems by adopting IoT with cloud computing. Integration and maintenance is also made very easy in the fourth generation system.

Fig. 8 – IoT SCADA Systems

Image Source: blog.seeb

These systems can report the state in real time using cloud computing. Thus intricate control algorithms can be implemented that are often used on traditional PLCs.

Applications of SCADA System

Supervisory Control and Data Acquisition systems are mainly used to monitor a wide data variety like currents, voltages, temperature, pressure, water levels etc. in several industries. If any abnormal conditions are detected, alarms at remote or central sites are triggered for operator alert. The various applications of SCADA Systems include:

  1. Power Generation & Distribution: Used to monitor current flow, voltage, circuit breaker functions. Also used in remotely switching on/ off of power grids.
  2. Water & Sewage System: Used by municipal corporations for regulating and monitoring water flow, reservoir status, pressure in distribution pipes, etc.
  3. Industries and Buildings: Used to control HVAC, central air conditioning, lighting, entry/ exit gates, etc.
  4. Oil and Gas Industries: Used for regulating and monitoring flow, reservoir status, pressure in distribution pipes, etc.
  5. Communication Networks: Used for monitoring and controlling servers, networks and nodes.
  6. Manufacturing: Used for managing inventories for controlling over manufacturing/ stocking. Also used for monitoring and regulating instrumentation, process and product quality.
  7. Public Transport: Used for regulating subway electricity, automating traffic signals/ railway crossing and live tracking of flights/ trains/ buses.

Advantages of SCADA System

The advantages of Supervisory Control and Data Acquisition system include:

  • Improvement in Service Quality
  • Improvement in Reliability
  • Reduction in operation and maintenance costs
  • Easy to monitor large system parameters
  • Real time information on demand
  • Reduction in Manpower
  • Value added services
  • Ease in Fault Detection and Fault Localization (FDFL)
  • Reduction in Repair Time (System Down Time)
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