Introduction to SCADA System:
SCADA stands for ‘Supervisory Control and Data Acquisition’. As the name suggests it is a control system which works on supervisory level, monitors and controls entire sites and collects data of each and every aspect or parameter which is to be measured using data acquisition. SCADA systems include PLCs which sometimes stand between SCADA software and hardware modules of SCADA. The main purpose of having SCADA system is to remotely control a system. For eg. if we have a plant of generation and transmission of power i.e. electricity in remote area and if we implement SCADA system to control and monitor our power generation plant then we do not have to physically go there and measure the wattage, voltages, currents or any parameter using multimeter . All the modules of SCADA will continuously monitor all the parameters related transformers, circuit breakers etc. This all information will be available for us 24/7 on the big screen which will show us without the delay of few micro seconds. If we see any fault or malfunctioning of any transformer, we can trip it without actually going in the plant by using SCADA system. This will save the humans from the dangers such as electrical shocks.
SCADA system mainly consists of input/output signal hardware, HMI (Human Machine Interface), RTU (Remote Terminal Unit), controllers, networks, communication infrastructure etc. The RTUs are nothing but the PLCs which are connected to the analog sensors and convert their signals to digital data and send it to supervisory systems i.e. data acquisition begins at RTU or PLC level and includes meter readings. SCADA system usually implements distributed database which is called as ‘tags’ or ‘points’. A point or tag is single input or output value monitored or controlled by the system. There are two types of points viz. hard and soft points. A hard point is a representative of actual input and output where as soft point is a result of logic and math operations applied to other hard and soft points.
Benefits of SCADA:
- When applied properly, SCADA system can help industries save time and money.
- You can eliminate the need for site visits for inspection, adjustments and data collection.
- SCADA system enables you to monitor operations in real time. It can auto-generate the reports also.
- Improves efficiency of the set up.
- Reduces operational costs.
Around the globe, SCADA is used to control:
- Electric power generation, transmission and distribution. In Mumbai, there are many companies which use SCADA for this purpose. One of the companies is BEST (Brihanmumbai Electric Supply and Transportation).
- Distribution of water supply.
- Traffic signals.
- Hotel buildings, offices, towers to control lighting, entry systems, refrigeration units, etc.
Now let’s understand architecture of SCADA.
Architecture of SCADA:
- Remote Terminal Unit and Master Terminal Unit:
SCADA hardware mainly consists of a number of Remote Terminal Unit (RTUs) which are connected with various sensors and actuators and are responsible for gathering the data and controlling the field parameters. They collect data and send them to a master station (Mater Terminal Unit or MTU) via a communication system. It is the heart of the SCADA system. The master station displays the acquired data and also allows the operator to perform remote control tasks. Generally, RTUs are nothing but PLCs. Often, in SCADA systems; the RTUs are located at remote locations. This distance varies from ten meters to thousand kilometers. It also consists of communication equipment such as telephone line, radio, cable, or satellite. Many RTUs store the data in their database and waits for a request from the MTU to send or transmit the data.
- SCADA software and programming:
SCADA software performs the tasks such as what and when to acquire and control, storing and accessing of acquired data, calculating various parameters, reporting and accounting, generating alarms, etc. Various SCADA soft wares are provided from different manufacturers for eg. WinCC from Seimens, RSView from Rockwell automation, Intouch from Wanderware etc. SCADA programming in a master or HMI is used for creating maps and diagrams which will give important information in case of an event failure or process failure. SCADA programming can be done using derived programming language or C language.
- Communication infrastructure between SCADA elements:
The communication between RTU in the field and MTU in the control center can be wired or wireless or through internet which provides bidirectional and uninterrupted communication. The network topology of the SCADA system network depends on the type of system or application it is intended for. SCADA architecture supports TCP/IP, UDP and other IP based communication protocols as well as industrial protocols like Modbus TCP, Modbus over TCP or Modbus over UDP. These all work over cellular, private radio or satellite networks.
- Human Machine Interface (HMI):
SCADA devices display the information on multiple huge screens, which combines both text and diagrams. It provides the provision for human operators to continuously monitor the operations and to intervene when necessary. SCADA HMI software consists of library of graphical symbols to which tag names are associated for a particular device or parameter such as ON/OFF status of switch, level information on tank, etc.
- Information Storage and Reports:
SCADA stores the collected data on either disks or permanent storage devices. The storing of data is performed on a cyclic basis which means once the period is completed which can be 40 days or 12 months or the log is full, it archives the data to permanent storage device. This allows the user to retrieve and analyze the data whenever it is needed. SCADA provides the report generation using SQL type queries. SCADA also facilitates to print and archive reports.
Now, we will see types of SCADA systems that can be considered as SCADA architectures of four different generations.
Types of SCADA system:
- First Generation: Monolithic or Early SCADA systems,
- Second Generation: Distributed SCADA systems,
- Third Generation: Networked SCADA systems and
- Fourth Generation: Internet of things technology, SCADA systems
- Monolithic or Early SCADA Systems:
In earlier times, during the time of first generation, monolithic SCADA systems were developed wherein the common network services were not available. Hence, these are independent systems without having any connectivity to other systems.
- Distributed SCADA Systems:
In the second generation, the sharing of control functions and data is distributed across the multiple systems connected to each other using Local Area Network (LAN). Hence, these were termed as distributed SCADA systems. These individual stations were used to share real-time information and commands. The cost and size of the station were reduced compared to the first generation system, as each system of the second generation was responsible for performing a particular task with reduced size and cost.
- Networked SCADA Systems:
The current SCADA systems are generally networked which communicate using Wide Area Network (WAN) Systems over data lines or phone. These systems use Ethernet or Fiber Optic Connections for transmitting data between the nodes frequently. These third generation SCADA systems use Programmable Logic Controllers (PLC) for monitoring and controlling various parameters in the system.
- Internet of Things (IOT) SCADA systems:
In fourth generation, the cost of the SCADA systems is minimized by adopting the internet of things technology with cloud computing. The maintenance and integration is also very easy for the fourth generation compared to the earlier SCADA systems. These SCADA systems are able to report state in real time by using the cloud computing facility.
Article Submitted by : Tanvi Shivgan