💾Embedded Systems Design Unit 17 – Industrial Control in Embedded Systems

Key Concepts and Terminology

• Industrial control systems (ICS) automated systems used to monitor and control industrial processes
• Supervisory Control and Data Acquisition (SCADA) systems centralized systems for monitoring and controlling geographically dispersed assets
  • Consists of supervisory computers, Remote Terminal Units (RTUs), and communication infrastructure
• Programmable Logic Controllers (PLCs) digital computers used for automation of industrial processes
  • Designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact
• Distributed Control Systems (DCS) control system in which the controller elements are distributed throughout the system
• Human-Machine Interface (HMI) the user interface in a manufacturing or process control system
  • Allows operators to monitor the state of a process, modify control settings, and manually override automatic control operations
• Fieldbus digital industrial network used for real-time distributed control
  • Examples include Profibus, Modbus, and DeviceNet
• Real-time systems systems in which the correctness of the system depends on both the logical results and the time at which the results are produced

Industrial Control System Architecture

• Typical ICS architecture consists of supervisory level, control level, and field level
• Supervisory level includes HMIs, engineering workstations, and data historians
  • Provides overall control and monitoring of the industrial process
• Control level includes PLCs and RTUs
  • Responsible for executing control algorithms and communicating with field devices
• Field level includes sensors, actuators, and other field devices
  • Directly interacts with the industrial process
• Communication between levels is achieved through industrial protocols like Modbus, Profibus, or Ethernet/IP
• Modern ICS architectures often incorporate Internet of Things (IoT) devices and cloud computing for remote monitoring and control
• Redundancy is often built into the architecture to ensure high availability and fault tolerance

Sensors and Actuators in Industrial Control

• Sensors measure physical quantities and convert them into electrical signals
  • Examples include temperature sensors, pressure sensors, flow meters, and proximity sensors
• Actuators convert electrical signals into physical actions
  • Examples include valves, motors, pumps, and relays
• Sensors and actuators are connected to PLCs or RTUs through input/output (I/O) modules
• Analog sensors produce continuous signals proportional to the measured quantity
  • Require Analog-to-Digital Converters (ADCs) to interface with digital systems
• Digital sensors produce discrete signals representing the presence or absence of a condition
• Actuators can be pneumatic, hydraulic, or electric
  • Pneumatic actuators use compressed air, hydraulic actuators use pressurized fluid, and electric actuators use electric motors
• Proper selection and placement of sensors and actuators are critical for effective industrial control

Communication Protocols for Industrial Systems

• Industrial communication protocols enable reliable and real-time data exchange between devices
• Modbus widely used protocol for communication between PLCs, RTUs, and HMIs
  • Supports serial (Modbus RTU) and Ethernet (Modbus TCP) communication
• Profibus fieldbus protocol for real-time communication in industrial automation
  • Variants include Profibus DP for high-speed communication and Profibus PA for process automation
• Ethernet/IP industrial protocol that uses standard Ethernet hardware and software
  • Allows seamless integration with enterprise networks
• OPC Unified Architecture (OPC UA) platform-independent protocol for industrial communication
  • Provides secure, reliable, and interoperable data exchange between systems
• Wireless protocols like WirelessHART and ISA100.11a are gaining popularity for industrial applications
  • Offer flexibility and reduced installation costs compared to wired networks
• Protocol selection depends on factors like data bandwidth, real-time requirements, and compatibility with existing systems

Real-Time Operating Systems (RTOS) in Industrial Control

• RTOS is an operating system designed to handle real-time applications
  • Provides deterministic behavior and fast response times
• Key features of an RTOS include preemptive multitasking, priority-based scheduling, and low latency
  • Preemptive multitasking allows high-priority tasks to interrupt lower-priority tasks
  • Priority-based scheduling ensures critical tasks are executed first
• Examples of RTOS used in industrial control include VxWorks, QNX, and FreeRTOS
• RTOS is used in PLCs, RTUs, and other embedded systems in industrial control
  • Ensures real-time performance and deterministic behavior
• RTOS selection depends on factors like hardware platform, memory footprint, and real-time requirements
• Proper design and implementation of tasks and interrupts are crucial for optimal RTOS performance
  • Tasks should have well-defined priorities and deadlines
  • Interrupts should be handled efficiently to minimize latency

Control Algorithms and Strategies

• Control algorithms determine how a system responds to inputs and disturbances
• Proportional-Integral-Derivative (PID) control widely used feedback control algorithm
  • Calculates control output based on the error between the setpoint and the measured process variable
  • Proportional term provides fast response, integral term eliminates steady-state error, and derivative term improves stability
• Feedforward control anticipates disturbances and adjusts control output accordingly
  • Useful for systems with known disturbances or long time delays
• Cascade control uses multiple control loops to improve performance
  • Inner loop controls a fast-responding variable, while the outer loop controls a slower-responding variable
• Model Predictive Control (MPC) advanced control strategy that uses a process model to predict future behavior
  • Optimizes control actions over a finite horizon while respecting constraints
• Fuzzy logic control uses linguistic rules to make control decisions
  • Suitable for systems with complex or poorly defined dynamics
• Selection of control algorithm depends on factors like system dynamics, performance requirements, and available sensors and actuators

Safety and Reliability Considerations

• Safety and reliability are critical in industrial control systems
• Safety Integrity Level (SIL) defines the required performance of a safety function
  • Higher SIL levels require more stringent design and testing
• Redundancy is often used to improve reliability
  • Examples include redundant sensors, actuators, and communication channels
• Fail-safe design ensures that a system enters a safe state in case of failure
  • Examples include spring-return actuators and de-energize-to-trip relays
• Functional safety standards like IEC 61508 and IEC 61511 provide guidelines for the design and implementation of safety-critical systems
• Regular maintenance and testing are essential for ensuring the long-term reliability of industrial control systems
  • Includes calibration of sensors, testing of safety functions, and replacement of worn-out components
• Cybersecurity measures are increasingly important for protecting industrial control systems from cyber threats
  • Includes network segmentation, access control, and encryption of communication channels

Industrial Control Applications and Case Studies

• Industrial control systems are used in a wide range of applications
• Process control applications include chemical plants, oil refineries, and power generation
  • Focus on maintaining process variables (temperature, pressure, flow) within desired ranges
• Manufacturing control applications include automotive assembly lines, semiconductor fabrication, and packaging machines
  • Focus on coordinating the operation of multiple machines and robots
• Building automation applications include HVAC systems, lighting control, and access control
  • Focus on optimizing energy efficiency and occupant comfort
• Transportation control applications include traffic management systems, railway signaling, and airport baggage handling
  • Focus on ensuring safe and efficient movement of people and goods
• Case study: Water treatment plant
  • Uses PLCs and SCADA system to monitor and control the treatment process
  • Sensors measure water quality parameters (pH, turbidity, chlorine), while actuators control pumps, valves, and chemical dosing
• Case study: Wind turbine control
  • Uses embedded controllers and pitch control algorithms to optimize power generation
  • Sensors measure wind speed, direction, and generator speed, while actuators adjust the blade pitch and generator torque
• Case study: Industrial robot control
  • Uses real-time motion control algorithms to achieve precise and repeatable movements
  • Sensors (encoders, vision systems) provide feedback on robot position and environment, while actuators (motors, grippers) execute the desired actions