Industrial control system is an all-encompassing term used for various automation systems and its devices, such as Programmable Logic Controllers (PLC), Human Machine Interface (HMI), Supervisory Control and Data Acquisition (SCADA) systems, Distributed Control Systems (DCS), Safety Instrumented Systems (SIS), and many others:
Programmable logic controllers, or PLCs, are at the heart of just about every Industrial control system. These are the devices that take data from sensors via input channels and control actuators via output channels. A typical PLC consists of a microcontroller (the brains) and an array of input and output channels. Input and output channels can be analog, digital, or network-exposed values. These I/O channels often come as add-on cards that attach to the backplane of a PLC. This way, a PLC can be customized to fit many different functions and implementations.
The programming of a PLC can be done via a dedicated USB or serial interface on the device or via the network communications bus that is built into the device or comes as an add-on card. Common networking types in use are Modbus, Ethernet, ControlNet, PROFINET, and others.
PLCs can be deployed as standalone devices, controlling a certain part of the manufacturing process, such as a single machine, or they can be deployed as distributed systems, spanning multiple plants in disperse locations with thousands of I/O points and numerous interconnecting parts.
The HMI is the window into the control system. It visualizes the running process, allowing inspection and manipulation of process values, the showing of alarms, and trending of control values. At its simplest form, an HMI is a standalone touch-enabled device that communicates via a serial or Ethernet encapsulated protocol. More advanced HMI systems can use distributed servers to offer a redundant supply of HMI screens and data:
The Supervisory Control and Data Acquisition system is a term used to describe a combined use of ICS types and devices, all working together on a common task. The following diagram illustrates an example SCADA network. Here, the SCADA network is comprised of all the equipment and components that together form the overall system. SCADA systems are often spread out over a wide geographical area as a result of being applied to power grids, water utilities, pipeline operations, and other control systems that use remote operational stations:
Closely related to the SCADA system is the distributed control system. The differences between a SCADA system and a DCS are very small and the two have become almost indistinguishable over time. Traditionally, though SCADA systems were used for automation tasks that cover a larger geographical area, meaning that parts of the SCADA system are located in separate buildings or facilities as where a DCS is more often confined to a single plant of facility. A DCS is often a large-scale, highly engineered system with a very specific task. It uses a centralized supervisory unit that can control thousands of I/O points. The system is built to last with redundancy applied to all levels of the installation, from redundant networks and network interface attached to redundant server sets to redundant controllers and sensors, all with creating a rigid and solid automation platform in mind.
DCS systems are most commonly found in water management systems, paper and pulp mills, sugar refinery plants, and so on:
Safety instrumented systems, or SIS, are dedicated safety monitoring systems. They are there to safely and gracefully shut down the monitored system or bring that system to a predefined safe state in case of a hardware malfunction. An SIS uses a set of voting systems to determine whether a system is performing normally:
