Understanding the Levels of a Complex SCADA System

A Supervisory Control and Data Acquisition (SCADA) system is used to monitor and control industrial processes. A complex SCADA system typically involves multiple layers of technology and functionality, often described in terms of different levels.

While specific implementations can vary, the architecture of a modern complex SCADA system is often aligned with standard models like the ISA-95 enterprise-control system integration model. This model defines several levels within an industrial enterprise:

• Level 0: The actual physical process. This is where the real-world action happens, like pumps running or valves opening.
• Level 1: Sensing and Actuating. This level includes devices like sensors and actuators that directly interact with Level 0. Programmable Logic Controllers (PLCs) or Remote Terminal Units (RTUs) are often present here, collecting data and sending commands.
• Level 2: Controlling. This level involves control systems that oversee the Level 1 devices. This is where the core SCADA software often resides, handling real-time control, monitoring, and alarming. Human-Machine Interfaces (HMIs) for operators to interact with the system are also at this level.
• Level 3: Manufacturing Operations Management. This level focuses on managing production workflow, scheduling, quality control, and maintaining production records. Manufacturing Execution Systems (MES) operate at this level.
• Level 4: Business Planning and Logistics. This is the enterprise level, dealing with overall business management, planning, and logistics. Enterprise Resource Planning (ERP) systems and Management Information Systems (MIS) are found here.

When discussing the levels of a complex SCADA system, the focus is often on the operational layers above the physical process. A common way to describe the architecture includes 4 key levels that directly relate to the SCADA functionality and its integration into the wider business:

• The field level (often combined Level 0 & 1)
• The control level (Level 2 - where SCADA software, PLCs/RTUs, HMIs operate)
• The supervisory/operations level (often combined Level 2 & 3 functionality)
• The enterprise/information level (Level 4)

Alternatively, some models simplify this, specifically within the context of a complex SCADA system's software and hardware structure itself, often identifying 4 main functional components or layers:

• Field Devices (Sensors, Actuators)
• RTUs or PLCs
• Communication System
• Master Terminal Unit (MTU) / Central SCADA Server with HMI

Considering the provided options and common industry models, describing a complex SCADA system as having 4 levels is a widely accepted representation focusing on the hierarchy from control devices up to enterprise integration.

Therefore, a complex SCADA system typically has 4 main operational or architectural levels.