Intro to Industrial Engineering
Table of Contents
Unit 14 Overview: Automation and Industrial Robotics
14.1 Fundamentals of Industrial Automation
14.2 Robotics in Manufacturing Systems
14.3 Programmable Logic Controllers (PLCs)
14.4 Computer Integrated Manufacturing (CIM)

Programmable Logic Controllers (PLCs) are the brains behind industrial automation. They're like mini-computers that control machines and processes in factories. PLCs read inputs, run programs, and control outputs in a continuous cycle, making them crucial for modern manufacturing.

PLCs use different programming languages, from simple ladder logic to complex structured text. They handle everything from basic on/off controls to advanced PID loops and data logging. Troubleshooting PLCs involves using diagnostic tools, analyzing programs, and solving common issues like timing problems or communication errors.

PLC Architecture and Function

Core Components and Operation

  • PLCs function as digital computers for automating industrial processes (control of machinery on factory assembly lines)
  • Basic PLC architecture comprises input modules, output modules, CPU, memory, and power supply
  • PLCs operate on a continuous scan cycle
    • Read inputs
    • Execute program
    • Update outputs
    • Perform housekeeping tasks
  • Utilize rugged, enclosed packaging for harsh industrial environments
    • Resistant to temperature fluctuations, vibration, and electrical noise

Input/Output Devices and Modularity

  • Input devices for PLCs include sensors (proximity, temperature), switches (limit, pressure), and transducers (flow, level)
  • Output devices encompass relays, motor starters, and solenoid valves
  • Modular design allows for easy expansion and modification
    • Add or remove I/O modules as automation needs change
    • Upgrade CPU or memory without complete system overhaul

Advanced Features

  • Modern PLCs incorporate networking capabilities
    • Ethernet, Profibus, Modbus for plant-wide communication
  • Data logging functionality for process analysis and troubleshooting
    • Record production data, alarm history, and system performance metrics
  • Human-Machine Interfaces (HMIs) for operator interaction
    • Touchscreen displays, push-button panels, or PC-based interfaces

PLC Programming Concepts

Programming Languages

  • Ladder Logic Diagram (LLD)
    • Most common PLC programming language
    • Based on relay logic schematics
    • Uses graphical symbols for contacts, coils, and function blocks
  • Function Block Diagram (FBD)
    • Graphical language representing functions between input and output variables
    • Interconnected blocks depict operations like AND, OR, timers, and counters
  • Structured Text (ST)
    • High-level text-based language similar to Pascal
    • Used for complex algorithms and data manipulation
    • Supports loops, conditional statements, and mathematical operations
  • Sequential Function Charts (SFC)
    • Programs sequential and parallel control processes
    • Breaks down processes into steps, transitions, and actions
    • Ideal for batch processes and state machines
  • Instruction List (IL)
    • Low-level text-based language similar to assembly
    • Used for simple, repetitive tasks
    • Efficient for small, resource-constrained PLCs

Data Types and Program Organization

  • PLC programming involves various data types
    • Boolean (TRUE/FALSE for digital I/O)
    • Integer (whole numbers for counters, timers)
    • Floating-point (decimal numbers for analog values)
    • String (text data for HMI displays, communication)
  • Program organization units in PLC programming
    • Main programs (primary control logic)
    • Subroutines (reusable code blocks)
    • Interrupt routines (handle time-critical or event-driven tasks)

PLC Programming Applications

Basic Control and Logic Operations

  • Develop ladder logic programs using basic elements
    • Normally open/closed contacts (represent input conditions)
    • Coils (represent output actions)
    • Timers (on-delay, off-delay)
    • Counters (up, down, cascading)
  • Implement interlocking and sequencing logic
    • Ensure safe operation of industrial processes
    • Prevent conflicting actions (motor reversals, valve operations)
  • Utilize mathematical and logical operations
    • Perform process calculations (flow rates, temperature conversions)
    • Make decisions based on multiple input conditions

Advanced Control Techniques

  • Design PID (Proportional-Integral-Derivative) control loops
    • Continuous process control applications (temperature, pressure, flow)
    • Tune PID parameters for optimal performance
  • Create data acquisition and logging systems
    • Use PLC memory to store historical data
    • Implement communication protocols for data transfer to databases or SCADA systems
  • Implement alarm and event handling routines
    • Manage abnormal process conditions (high temperature, low pressure)
    • Handle system faults (sensor failures, communication errors)

Human-Machine Interface Development

  • Develop HMI screens for operator interaction
    • Create intuitive displays for process monitoring
    • Design control interfaces for manual interventions
    • Implement security features (user authentication, access levels)

PLC Troubleshooting

Diagnostic Tools and Techniques

  • Utilize built-in diagnostic tools and indicators on PLCs
    • LED status lights for power, run status, and fault conditions
    • Error code displays for specific fault identification
  • Implement online monitoring and forcing of I/O points
    • Isolate problems in field devices or wiring
    • Simulate input conditions for testing purposes
  • Analyze program execution using debugging features
    • Breakpoints to pause program at specific points
    • Single-step execution for detailed logic analysis
    • Watch windows to monitor variable values in real-time

Common Issues and Resolution Strategies

  • Identify and resolve timing issues in PLC programs
    • Race conditions where outcomes depend on execution order
    • Critical path analysis to optimize program performance
  • Troubleshoot network communication problems
    • Verify proper configuration of communication parameters
    • Use protocol-specific tools (Modbus scanner, Profibus tester)
  • Perform systematic fault-finding procedures
    • Check power supplies for proper voltage levels
    • Inspect I/O modules for loose connections or blown fuses
    • Test field wiring for continuity and proper termination

Maintenance and Recovery Strategies

  • Implement backup and version control for PLC programs
    • Regular backups of program and configuration files
    • Document changes and maintain revision history
  • Develop recovery procedures for system failures
    • Create step-by-step guides for restoring PLC programs
    • Establish spare parts inventory for critical components

Key Terms to Review (22)

Modbus: Modbus is a communication protocol used for transmitting information between electronic devices, primarily in industrial environments. It is a widely adopted standard for connecting programmable logic controllers (PLCs) and other industrial devices, allowing for seamless integration and control of automation systems. By enabling devices to communicate over various types of networks, Modbus plays a critical role in facilitating data exchange in industrial automation and process control.
Profibus: Profibus (Process Field Bus) is a standard for fieldbus communication in industrial automation systems, facilitating data exchange between devices such as sensors, actuators, and controllers. It plays a crucial role in enhancing the efficiency and interoperability of various components in automated processes, promoting seamless communication in complex manufacturing environments.
Ethernet: Ethernet is a widely used networking technology that allows devices to communicate over a local area network (LAN) through a series of protocols for data transmission. This technology supports both wired and wireless connections and is fundamental for linking various devices, including computers and Programmable Logic Controllers (PLCs), to facilitate data exchange and control in industrial environments.
ANSI/ISA-88: ANSI/ISA-88 is a set of standards that provides a framework for the design and implementation of batch control systems in industrial processes. This standard focuses on defining the terminology, models, and methodologies necessary for automating batch processes, ensuring consistency, flexibility, and efficiency across various manufacturing environments.
First PLC: The term 'First PLC' refers to the initial introduction of Programmable Logic Controllers (PLCs) in industrial automation, revolutionizing the way machines and processes are controlled. This breakthrough technology replaced traditional relay systems, allowing for greater flexibility, scalability, and ease of programming. The First PLC represented a significant advancement in manufacturing efficiency and reliability, setting the stage for modern automated systems.
Debugging: Debugging is the process of identifying, analyzing, and removing errors or bugs in software or control systems to ensure they function as intended. This crucial step often involves testing, monitoring, and reviewing code or programming logic to pinpoint issues that may lead to system malfunctions or incorrect outputs, particularly in programmable logic controllers (PLCs). Effective debugging enhances system reliability and efficiency by systematically resolving problems that can disrupt operations.
Scan time: Scan time refers to the duration a programmable logic controller (PLC) takes to execute a complete cycle of input scanning, processing logic, and output updating. This measurement is crucial as it directly affects the responsiveness and efficiency of automated systems, ensuring that the PLC can react promptly to changes in inputs and maintain accurate outputs.
Fault diagnosis: Fault diagnosis is the process of identifying, analyzing, and determining the cause of malfunctions in a system. This process is crucial for maintaining the reliability and efficiency of systems, particularly in automated environments where equipment failures can lead to significant downtime or safety hazards. It involves using various techniques, including systematic testing, data analysis, and fault tree analysis, to pinpoint issues and ensure that systems function as intended.
Modicon 084: The modicon 084 is a type of programmable logic controller (PLC) developed by Modicon, which was one of the pioneers in the field of PLC technology. It is designed for industrial automation and control, allowing users to program sequences of operations for machinery and processes in a flexible and efficient manner. The modicon 084 supports various programming languages, offers digital and analog input/output capabilities, and can be integrated with other industrial devices to streamline automation processes.
IEC 61131: IEC 61131 is an international standard for programmable controllers, defining the programming languages, functionalities, and communication protocols used in industrial automation systems. It aims to ensure compatibility and interoperability among different systems and devices, making it essential for the development and integration of programmable logic controllers (PLCs) in various industries.
SCADA Systems: SCADA systems, or Supervisory Control and Data Acquisition systems, are crucial for monitoring and controlling industrial processes. They gather real-time data from remote locations, allowing operators to manage infrastructure such as power plants, water treatment facilities, and manufacturing lines efficiently. These systems integrate hardware and software to provide centralized control and oversight, making it easier to maintain operational efficiency and safety.
Pid control loops: PID control loops are feedback control systems that use proportional, integral, and derivative actions to maintain a desired output by adjusting input variables. This method is widely used in industrial automation and processes for its effectiveness in achieving precise control over various parameters like temperature, pressure, and flow rates.
HMI: HMI, or Human-Machine Interface, refers to the systems and devices that allow humans to interact with machines and control them effectively. This interface plays a crucial role in the operation of automated systems, particularly in environments using Programmable Logic Controllers (PLCs), by providing operators with visual feedback, input options, and monitoring capabilities. HMIs enhance user experience and improve operational efficiency by translating complex data into understandable formats.
Ladder logic diagram: A ladder logic diagram is a graphical programming language used to develop software for programmable logic controllers (PLCs), resembling the rungs of a ladder. This visual representation allows users to easily understand and implement control processes, making it a standard in industrial automation. Ladder logic diagrams use symbols to represent electrical components and their connections, facilitating the design and troubleshooting of control systems.
Instruction list: An instruction list is a low-level programming language used primarily for programming programmable logic controllers (PLCs). It consists of a series of instructions written in a sequential manner, which the PLC executes to control machinery and processes. This format allows for efficient execution and monitoring of tasks, making it a vital aspect of automation in industrial settings.
Input/output modules: Input/output modules are components of a programmable logic controller (PLC) that facilitate communication between the PLC and external devices or systems. They are essential for receiving data from input devices, such as sensors and switches, and for sending commands to output devices like motors and lights. By managing the flow of information, input/output modules play a critical role in automating processes and enabling control within industrial environments.
Central Processing Unit: The central processing unit (CPU) is the primary component of a computer that performs most of the processing inside the system. It interprets instructions from programs and executes them, acting as the brain of the computer. In the context of programmable logic controllers (PLCs), the CPU plays a critical role in controlling industrial processes by executing control algorithms and managing input/output operations.
Structured text: Structured text is a high-level programming language used to program programmable logic controllers (PLCs). It allows for the creation of complex control algorithms using a more readable and organized format, making it easier for engineers to understand and maintain the code. This text-based approach enables better integration with other programming paradigms and simplifies the development process, particularly for those familiar with traditional programming languages.
Data logging: Data logging is the process of collecting and storing data over time to monitor and analyze various parameters. This technique is crucial for tracking performance, identifying trends, and ensuring systems operate efficiently, especially in automation and control environments where Programmable Logic Controllers (PLCs) are utilized to manage processes.
Sequential Function Charts: Sequential function charts (SFCs) are a graphical programming language used in programmable logic controllers (PLCs) that represent the sequence of operations in a process. They allow for the visualization of control processes by breaking down complex operations into manageable steps, showing the transitions between different states and actions within a system.
Function Block Diagram: A function block diagram (FBD) is a graphical representation used to describe the behavior of programmable logic controllers (PLCs) by illustrating the functions and the flow of data between them. This method is designed to simplify complex control systems, allowing users to visualize and organize the logic of processes clearly. Function block diagrams employ blocks to represent functions and lines to show connections, which facilitates easier programming and troubleshooting of automation systems.
Ladder logic: Ladder logic is a programming language used to develop software for programmable logic controllers (PLCs). It visually resembles an electrical relay logic diagram, using two vertical rails and horizontal rungs that represent the control logic. This graphical format makes it easy for engineers and technicians to understand and troubleshoot complex control systems.