SCADA systems

SCADA systems have become a crucial element in the automation and control of industrial plants and a variety of commercial processes such as scheduling and monitoring trains etc. They serve to enhance human and plant efficiency, improve decision making, reduce plant downtime and generate a variety of alarms, reports etc.

The acronym SCADA represents Supervisory Control and Data Acquisition typically implemented through a combination of hardware and software to enable industrial organisations to:

Inductive Automation

A Long History

Supervisory control had its origins in the 1940s as the need to reset remote electrical substations quickly became prevalent. Although the link between the substations and the control room was hardwired, with a dedicated pair of wires for each piece of equipment, the benefits outweighed the cost of the system and its inherent limitations.

It became apparent that it was possible to operate multiple devises on a single pair of wires, known as multiplexing. The inherent risk with this new system was that the incorrect piece of equipment may be activated/deactivated. The overcome this risk a select-check-operate schema was developed that resulted in a command being send to a specific devise, an acknowledge signal being returned by the devise and finally the instruction to operate was given.

The need grew not only to be able to switch equipment on and off but also to get information about analogue values such as current, voltage and wattage. Due to the long distances between power stations, substations and control rooms it was not possible to transmit these values directly over wired pairs. Pulse and frequency modulated systems gradually developed during the 1950s enabling utilities to transmit analogue values over pilot wires, power lines or microwave channels. These changes coincided with the development of solid state devices replacing mechanical relays enabling more reliable and faster data communication. Values where however still recorded by hand giving rise to the birth of data loggers that could record the values that operators previously had to write out manually.

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By the late 1960s hardware and communication has evolved to the extent that it was possible to continuously scan digital and analogue inputs at remote locations and communicate these values back to a master computer or control unit (MTU). The units responsible for this task became known as Remote Terminal Units (RTUs). In some instances, the units also incorporate logic functions and could continue to function in the events of power outages (they had battery backups) or in the event of communication losses to the MTU. RTUs where typically designed for low power, bandwidth and low maintenance and had limited programming capability. The initial versions were all equipped with proprietary firmware and communications protocols.

Human/Machine Interfaces (HMIs)

Early human/machine interfaces typically consisted of panels fitted with indicator lights and push buttons. These panels varied in size and complexity from simple to very large and sophisticated. With the introduction of Cathode Ray Tubes in the 1970s it became possible to display plant layouts graphically on a computer screen although the early models where nothing more than simple line diagrams. During the 80s the complexity increased and many of the functions previously hardwired through control panels could be incorporated into the HMIs. Operators interacted directly with the elements on the screen and items such as push buttons, sliders, controllers etc. became part of a Graphical User Interface. Today HMIs are found in both the control room and the plant floor and are often equipped with touch screens.

Over time Programmable Logic Controllers (PLCs) began to replace RTUs in many remote sites as complexity increased and the demand for improved logic routines, processing power and open standards grew. Today SCADA systems interact with both PLCs and RTUs as well as a variety of proprietary controllers such as flow computers, batch controllers etc.

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If you would like to know more

Communication media and protocols also continues to evolve and although there is still a large installed base of historical serial communication methods such as RS232, RS485 and leased lines in operation there is a shift toward newer TCP/IP and IP methods over media such as fibre and wireless radio links. Consequently, networking equipment such as switches, routers and firewalls have all become part of modern SCADA networks. Integration of SCADA networks into corporate networks have also become a much more prevalent discussion topic as the need for faster reporting cycles and management information have increased.

The introduction of modern IT standards, technologies and practices into SCADA ecosystems have greatly improves the cost, availability, and security of SCADA systems. The inclusion of databases such as SQL also make it easier to integrate SCADA systems into MES/MIS and ERP systems. Just as with the adoption of more open communication standards we are also seeing the advent of less restrictive licensing models that make SCADA pricing more transparent and affordable.

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Common Component of SCADA Systems

The most common components found in just about any SCADA systems include:

[list type=”unorder”][listitem]Historian: a database with a fixed schema for storing time stamped historic and event data. Historian schemas are generally locked and offer limited accessibility[/listitem][listitem]Trending modules: provide for both real time and historical data trends over multiple timelines[/listitem][listitem]Alarm Management: the ability to prioritise alarms, filter alarm types, acknowledge and suppress alarms as well as reduce nuisance alarms[/listitem][listitem]Reporting modules[/listitem][listitem]Database connections: time stamped data can also be stored in SQL databases which offer additional opportunities for data collection integration into third party systems such as MES/MIS and ERP systems[/listitem][/list]

[divider customsize=”20″][tblock tag=”h4″ title=”Research In Mechanical”]Factors to Consider[/tblock]

There are many factors to consider when selecting a SCADA system, a few of which are listed below:

[tblock tag=”h4″ title=”Research In Mechanical”]Contact Us[/tblock]

If you have any questions with regards to the selection or implementation of a SCADA system please feel free to contact us.

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