General Architecture

 

Supervisory Control And Data Acquisition (SCADA) is an automation control system used in industries such as energy, water, et cetera, for the purpose of monitoring the needs and abilities of many separate devices. SCADA systems are intended to reduce the need for constant human interaction with the operation of devices. It also implements a distributed database, or tag database, that contains tags or points throughout the plant. A single input and an output value is represented by these points which can be monitored or controlled by SCADA system in the centralized control room. Most common things a SCADA system acquire is metadata, like programmable logic controller (PLC) register paths and alarm statistics.

There are five essential components of any SCADA system (Inductive Automation):

• Human Machine Interface (HMI)

• SCADA Server / Master Terminal Unit

• Remote Terminal Units (RTUs)

• Programmable Logic Controllers (PLCs)

• Communication Infrastructure

HMI applications or specialized panels are used by human operators to program and monitor the PLCs (All Instrumentation). The purpose of the SCADA server is to gather data from each PLC and send out commands or operations in return. RTUs are used for connecting sensors and converting their signals to digital data and sending it to the supervisory system, where it is stored in distributed database (Inductive Automation). PLCs are used as field devices because they are more multipurpose and inexpensive than the RTUs, which are used for specific processes. Data from RTU/PLCs is relayed by the communication infrastructure, which can run along electric grids, water supplies, and pipelines. The most absolute link for SCADA system to operate properly is communication. In order for the system to be successful, it must be able to ensure the continuous, fast and accurate transmission of data to each recipient.

​

There are other common elements of typical SCADA networks but which are not required for operation. Integration into premises security, and integration into the world wide web to receive remote commands and disseminate information.

A SCADA system does not need to be one which has been purchased from a specialized supplier. For supervisory control of small operations, a web server may be used as the core of the system. Some common requirements of this server would include access to a query-capable database (Greenfield), detailed logs of input and actions taken, and full privilege settings to allow full data writing on subordinate devices.

 

This diagram represents the typical SCADA network configuration:

​

​

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Common Transmission Methods

 

A SCADA server may connect to one or more parts in a different manner than others. It is not required that all major components of the system be localized to the same building. Nor is it required that all major components be part of the same network. SCADA systems have a range of possible transmission methods, and can exist anywhere on a scale from completely localized to completely distributed. The following are common transmission mediums (University of Kentucky):

 

Ethernet - A typical wired connection to a Local Area Network (LAN). Cheap and able to restrict the number of possible access points to the network, but limits the range of devices to being prepositioned along the cables. May be combined with a VPN to create two or more remote locations.

 

Radio - May run on licensed radio frequencies to reduce communication failure rates, and does not require continual connection to the internet as administered by an internet service provider. Potentially long range without making use of the world wide web, but requires repeaters and visibility through the placement of directional antenna for long distances. (Wendt)

 

WiFi - A typical wireless connection to a Wireless Local Area Network (WLAN). Cheap but difficult to restrict the number of possible access points. Does not require visibility, but is limited by distance. Devices may be moved around while in range of a router or repeater.

 

Regardless of the medium used in the network, the presence of firewalls between SCADA systems, RTUs and the outside internet is common and prudent (Automation). Firewalls may mitigate the likelihood of an authorized user gaining access to sensitive systems or information, both from outside the network and potentially inside. As with typical networks, firewalls may only block activities at their point of placement in the network, so multiple devices may be needed in a typical SCADA network.

 

Differences in Critical Infrastructure Sectors

​

Communication:  

 

SCADA systems in the communication sector are used to govern many individual server machines and ensure continual operation for internet service (Applications of SCADA). A SCADA system may control the update of operating systems and device drivers, and take constant measurement of device temperature and user loads. If a server must be taken offline, or another must be added temporarily to balance user loads, the SCADA system has the ability to do so.

​

Emergency Management:

 

Traffic monitoring by SCADA systems can be fed through traffic cameras and pressure plates. Video surveillance may be used to determine the type of situation that requires responders. A SCADA server may interface with law enforcement databases to perform facial recognition of video surveillance in a situation involving a suspect pursuit. Video surveillance may also be sent to first responders enroute to an emergency, to know the number of people present and where the emergency is.
 

Power:

 

Because power generation is heavily dependent on the presence of natural resources, a SCADA system in the power sector may need to take data from geographical surveys (Agarwal), GPS locations of transport vehicles in motion, or wind and temperature readings to be able to predict what power output it is capable of in the near future. A SCADA system would be responsible for the storage of energy in batteries, to be used in case of lowered output or outage (Electrical Technology). A power distribution and grid management SCADA system requires connection to many remote stations, which have their own data inputs from wide areas of operation.

​
 

Transportation:

 

SCADA systems are used to ensure the continuous operation of public transportation and traffic control systems. Not all traffic lights are governed by SCADA systems - they may be based on independent timers or weight sensors. But for dense urban areas, SCADA may be used to govern traffic lights to reduce congestion and dilute traffic across the area of responsibility (Srivastava).
 

Water:

 

SCADA systems in the water sector may fit into one of multiple roles, such as being responsible for one water plant or being responsible for the transportation of water across multiple plants (University of Kentucky). A system that encompasses only one plant may take on the needs of securing the premises against intrusion and record the availability of water reservoirs (Agarwal), while a system that distributes water must be able to balance water distribution according to needs and available resources.

 

Works Cited

 

“Introduction to Human Machine Interface (HMI).” All Instrumentation, 10 June 2017, www.allinstrumentation.com/control-system/plc-system/introduction-human-machine-interface-hmi/.

 

Agarwal, Tarun, et al. “What is SCADA System and Its Applications in Power Systems.” Buy Electronics & Electrical Projects in India, 12 Apr. 2016, www.edgefx.in/scada-applications-in-power-system/.

 

“SCADA/Business Network Separation: Securing an Integrated SCADA System.” Automation.com Real-Time Information for the Automation Professional TM, www.automation.com/library/articles-white-papers/hmi-and-scada-software-technologies/scadabusiness-network-separation-securing-an-integrated-scada-system.

 

“Applications Of SCADA In Common Industries.” Applications of SCADA - Telecom, Utilities, Manufacturing and Food Production, www.dpstele.com/scada/applications-of.php.

 

Greenfield, David. “Want to Build Your own SCADA? Here's a Guideline.” Want to Build Your own SCADA? Here's a Guideline, 19 Sept. 2014, “What is SCADA?” Inductive Automation, inductiveautomation.com/what-is-scada. www.automationworld.com/article/technologies/scada/want-build-your-own-scada-heres-guideline.

 

“SCADA Systems for Electrical Distribution.” Electrical Technology, 13 Sept. 2015, www.electricaltechnology.org/2015/09/scada-systems-for-electrical-distribution.html.

 

Srivastava, Mohit Dev, et al. “SMART TRAFFIC CONTROL SYSTEM USING PLC and SCADA.” International Journal of Innovative Research in Science, Engineering and Technology, Research and Reviews, 1 Jan. 1970, www.rroij.com/open-access/smart-traffic-control-system-usingplc-and-scada.php?aid=44962.

 

“Communication Network.” University of Kentucky, University of Kentucky. http://www.uky.edu/WDST/PDFs/[23]%20Communications%20network.pdf

 

Wendt, Curt, et al. “Designing and Implementing Radio Based SCADA Systems – Lessons Learned.” Water & Wastewater Instrumentation Symposium, Water & Wastewater Instrumentation Symposium, 2003. http://isawwsymposium.com/wp-content/uploads/2012/01/Wendt-Murphy-Nelson_RadioBasedSCADASystemsLessons_Paper_WWID2003.pdf