Industrial Control System

A DCS is used to control production systems spread within the same geographical location. Such systems are primarily used for large, complex, and distributed processes that are carried out in industries such as chemical manufacturing and nuclear plants, oil refineries, water and sewage treatment plants, electric power generation plants, and automobile and pharmaceutical manufacturing.

System Characteristics:

• Highly engineered and large-scale control system
• Used to perform industry-specific tasks
• Contains a centralized supervisory control unit used to control multiple local controllers
• Manages thousands of input/output (I/O) points and various field devices

Operational Features:

• Employs various feedback and feedforward loops along with key product conditions
• Uses targeted set points for process control
• Operates using a centralized supervisory control loop (SCADA and MTU)
• Connects groups of localized controllers (RTU/PLC)
• High level of redundancy at every level (I/O controllers to network level)

Advantages:

• Adaptability and flexibility in controlling distributed discrete field devices
• Scalable design (large integrated system or modular integration)
• Constant development with new technologies (wireless systems, remote transmission, data historian, embedded web servers)

• SCADA

SCADA is a centralized supervisory control system that is used for controlling and monitoring industrial facilities and infrastructure. Many organizations incorporate SCADA systems for the automation of complex industrial processes, measuring trends in real time, and the detection and correction of problems.

Applications:

• Transportation of oil and gas
• Wastewater treatment and management
• Pipeline operations
• Telecommunications
• Power grids
• Building automation
• Public transportation systems

System Architecture:

• Centralized system providing supervisory control and real-time data acquisition
• Hardware and software components for data collection and transmission
• Data storage in long-term devices (data historian)
• Integration of data acquisition system with data transmission system and HMI software

Components:

• Control Server (SCADA-MTU): Processes and controls information from RTUs
• Communication Devices: Network cables, radio devices, telephone lines
• Field Sites: Geographically distributed PLCs, RTUs for equipment monitoring and control
• IEDs: Intelligent Electronic Devices with communication interfaces for sensors and equipment

Operational Features:

• Collects information from field devices and transmits to central computer
• Displays information graphically or textually to operators
• Enables real-time control and monitoring from central location
• Programmed for monitoring parameters, acceptable ranges, and response actions
• Fault-tolerant with redundant systems
  

• Programmable logic controller

Programmable Logic Controller (PLC)

A PLC is a real-time digital computer used for industrial automation. PLCs are considered more than just digital computers in various industrial control systems due to their extraordinary features such as robust construction, ease of programming, sequential control, ease of hardware use, timers and counters, and reliable controlling capabilities.

Applications:

• Steel, automobile, energy, chemical, glass, paper, cement manufacturing industries

System Components:

1. CPU Module

• Central processor and memory component
• Performs data computations and processing
• Memory includes RAM (user programs) and ROM (operating systems, drivers, application programs)
• Retentive memory preserves programs during power failures

2. Power Supply Module

• Converts AC to DC power
• 5V DC for computer circuitry
• 24V DC for sensors and actuators in some systems

3. I/O Modules

Digital I/O Module:

• Connects digital sensors and actuators (ON/OFF switching)
• Works with multiple digital inputs/outputs
• Supports both AC and DC voltages

Analog I/O Module:

• Connects analog sensors and actuators
• Includes analog-to-digital converter
• Processes analog signals through CPU module

Communication I/O Module:

• Exchanges information between communication network and remote CPU

Primary Functions:

• Continuous monitoring of input values from sensors
• Generation of outputs for actuator operation
• Replaces drum sequencers, hard-wired relays, and timers
• Enables automatic machinery and system operation without human intervention

!Figure 18.76: PLC architecture

A BPCS is responsible for performing process control and monitoring for industrial infrastructure. It is a system that responds to input signals from processes and associated equipment to generate output signals that allow the process and its associated equipment to operate based on an approved design control strategy.

Characteristics:

• Dynamic and highly adaptable to changing process conditions
• Applicable to various control loops (temperature, batch, pressure, flow, feedback, feedforward)

Applications:

• Chemical, oil and gas, food and beverages industries

Key Functions:

• Trending and alarm/event logging facilities
• Operator interface through HMI console for system monitoring and control
• Process optimization for enhanced product quality
• Production data report generation
• Sequencing, timing, and coordination of batch process steps
• Critical safety interlocks to prevent unsafe equipment operation
• Recipe storage and retrieval (formulas, process steps, production parameters)
• Integration with business and engineering systems

Role in Safety:

• First layer of protection against unsafe conditions
• Pushes performance limits to attain desired results
• Lacks diagnostic routines for system flaw identification

!Figure 18.77: BPCS architecture

A safety instrumented systems (SIS) is an automated control system designed to safeguard the manufacturing environment in case of any hazardous incident in industry. They monitor and perform "specific control functions" to shut down the monitored system or bring it to a predefined safe state to reduce the adverse impacts of an incident.

Purpose:

• Essential component of risk management strategy
• Uses layers of protection to prevent unsafe operating conditions
• Overrides BPCS when operating beyond normal parameters

Examples:

• Fire and gas systems
• Safety interlock systems
• Safety shutdown systems

System Components:

Field Sensors

• Collect and measure process parameters (temperature, pressure, flow)
• Predict safe/unsafe operating states
• Types: pneumatic, electric switches, smart transmitters

Logic Solvers

• Decide necessary actions based on gathered information
• Handle failsafe and fault-tolerant situations
• Execute pre-programmed actions to avoid risks

Final Control Elements

• Implement actions determined by logic controller
• Bring system to safe state (equipment or process shutdown)
• Typically pneumatically activated on-off valves controlled by solenoid valves

Functional Requirements:

• Determined through HAZOP, LOPA, risk graphs
• Works independently from other control systems
• Requires constant testing and cybersecurity assessment

!Figure 18.79: SIS architecture