What is SCADA?

Supervisory Control and Data Acquisition — real-time industrial monitoring and control.

How SCADA Works

A SCADA system is built on four key components:

• Field Devices: PLCs (Programmable Logic Controllers), RTUs (Remote Terminal Units), and sensors that read physical process values — temperature, pressure, speed, counts.
• Communication Network: Industrial protocols (Modbus, Profinet, OPC UA, DNP3) carry data from field devices to the SCADA server.
• SCADA Server (MTU): The Master Terminal Unit aggregates all incoming data, runs alarm logic, stores historian data, and exposes a data interface to operator consoles.
• HMI (Human-Machine Interface): Operator screens showing process mimic diagrams, real-time values, alarm lists, and trend charts. Operators can issue commands (start/stop, setpoint changes) back to PLCs.

SCADA, DCS, MES & ERP — The ISA-95 Stack

Industrial automation is structured in layers defined by ISA-95. Understanding where SCADA fits prevents confusion with adjacent systems:

Key distinction: SCADA sees individual machine signals; MES sees production orders, OEE metrics, and quality records aggregated across many machines. They are complementary, not competing.

SCADA vs DCS — What's the Difference?

DCS (Distributed Control System) is an integrated hardware+software platform designed for continuous process industries such as oil refining, chemicals, and power generation. Control logic runs in the DCS controllers themselves; the system is designed for millisecond-speed closed-loop control with very high reliability.

SCADA is software-centric and widely used in discrete manufacturing, utilities, and geographically distributed infrastructure (pipelines, water treatment). SCADA supervises and logs at second-level intervals rather than running tight control loops.

In modern plants the distinction is increasingly blurred — both expose OPC UA interfaces, and many DCS vendors offer SCADA-like historian and HMI functionality.

OPC UA: The Bridge Between SCADA and MES

OPC UA (IEC 62541) is the standard industrial communication protocol that allows SCADA systems and PLCs to publish data in a standardised, secure, platform-independent way. A MES or semantic engine acts as an OPC UA client — it subscribes to signal changes on the OPC UA server (the SCADA or PLC).

This eliminates proprietary drivers and vendor lock-in. Live Availability signals (machine running/stopped), Performance signals (actual vs ideal speed), and Quality signals (good/reject counts) flow from SCADA through OPC UA into the MES where they are contextualised into OEE metrics and loss classifications.

Frequently Asked Questions