Lesson 1: Introduction to Programmable Logic Controllers (PLCs) Flashcards
What is a PLC?
Programmable Logic Controllers
Define PLC.
A PLC is a user-friendly, microprocessor-based specialized computer that carries out control functions of various types and levels of complexity. It can be programmed, controlled, and operated by someone with little computer knowledge.
A PLC can be used for industrial automation, automating specific processes, machine functions, or entire production lines.
Cite few examples of industries where PLCs are used.
- Robots manufacturing and control
- Car park control
- Train control station system
- Food processing
- Materials handling
- Machine tools
- Traffic control system
- Conveyor system etc.
What are the advantages of a PLC?
- Flexibility
- Implementing changes and correcting errors
- Large quantities of contacts
- Lower cost
- Pilot running
- Visual Observation
- Speed of operation
- Ladder or Boolean programming method (Using contacts and coils or mnemonics)
- Reliability and maintainability (Repairance is easy.
Reliable because we use semiconductors which are mechanical in nature.) - Simplicity of ordering control system components
- Documentation
- Security
- Ease of changes by reprogramming
What are the disadvantages of using PLC?
- Newer technology
- Fixed program applications
- Environmental considerations
- Fail-safe operation
E.g. if the system suddenly shuts down and turns on, it damages the system that’s why we have a fail-safe circuit now. - Fixed-circuit
What is the PLC System (its components)?
- Central Processing Unit (CPU)
- Processor
- Memory
- Power Supply - Programmer/Monitor (PM)
- I/O Modules
What are the types of computer?
- Data Processing Computer
- Process Control Computer
PLC Scanning Procedure
Input terminals -> Input status table -> User program -> Output status table -> Output terminals
Key Differences in Computer Software Development
Computer science and industrial process control software development differ primarily in their input/output interfaces, with desktop computers relying on traditional keyboards and mice for input and displays and printers for output, while process control systems utilize specialized sensors (e.g., motion, heat) for input and control physical devices (e.g., motors, lights) for output.
its main function is to control manufacturing and industrial processes (Robots, Machinery, Assembly Lines, etc.) Such computers are said to be event driven.
Process Control Computer
these are microcomputers like IBM’s and Apple with powerful systems and applications software that allows you to play games, do word processing, create computer aided designs (CAD), and explore the wonders of the Nile River.
Data processing computer
has terminals into which the users enters outside process electrical signals.
Input modules
has another set of terminals that send action signals to the process.
Output module
is the keyboard on which the program instructions are type by the user.
the programmer
is a TV like screen on which operating information is displayed.
monitor
