Industrial control system

Networking allows the use of local or remote SCADA operator interfaces, and enables the cascading and interlocking of controllers.

The operator interfaces which enable monitoring and the issuing of process commands, such as controller setpoint changes, are handled through the SCADA supervisory computer system.

[6] The SCADA software operates on a supervisory level as control actions are performed automatically by RTUs or PLCs.

They can be designed for multiple arrangements of digital and analog inputs and outputs, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact.

Effectively this was the centralisation of all the localised panels, with the advantages of reduced manpower requirements and consolidated overview of the process.

It also required continual operator movement within a large control room in order to monitor the whole process.

It enabled sophisticated alarm handling, introduced automatic event logging, removed the need for physical records such as chart recorders, allowed the control racks to be networked and thereby located locally to plant to reduce cabling runs, and provided high-level overviews of plant status and production levels.

[8] It was soon adopted in a large number of other event-driven applications as varied as printing presses and water treatment plants.

SCADA's history is rooted in distribution applications, such as power, natural gas, and water pipelines, where there is a need to gather remote data through potentially unreliable or intermittent low-bandwidth and high-latency links.

A SCADA system uses remote terminal units (RTUs) to send supervisory data back to a control centre.

Many PLC platforms can now perform quite well as a small DCS, using remote I/O and are sufficiently reliable that some SCADA systems actually manage closed-loop control over long distances.

With the increasing speed of today's processors, many DCS products have a full line of PLC-like subsystems that weren't offered when they were initially developed.

In 1993, with the release of IEC-1131, later to become IEC-61131-3, the industry moved towards increased code standardization with reusable, hardware-independent control software.

New hardware platforms and technology have contributed significantly to the evolution of DCS and SCADA systems, further blurring the boundaries and changing definitions.

[10] MOSAICS addresses the Department of Defense (DOD) operational need for cyber defense capabilities to defend critical infrastructure control systems from cyber attack, such as power, water and wastewater, and safety controls, affect the physical environment.

Panel mounted controllers with integral displays. The process value (PV), and setvalue (SV) or setpoint are on the same scale for easy comparison. The controller output is shown as MV (manipulated variable) with range 0-100%.
A control loop using a discrete controller. Field signals are flow rate measurement from the sensor, and control output to the valve. A valve positioner ensures correct valve operation.
Functional manufacturing control levels. DCS (including PLCs or RTUs) operate on level 1. Level 2 contains the SCADA software and computing platform.
Siemens Simatic S7-400 system in a rack, left-to-right: power supply unit (PSU), CPU, interface module (IM) and communication processor (CP).
A pre-DCS era central control room. Whilst the controls are centralised in one place, they are still discrete and not integrated into one system.
A DCS control room where plant information and controls are displayed on computer graphics screens. The operators are seated as they can view and control any part of the process from their screens, whilst retaining a plant overview.