Microcomputer based controllers and programmable logic controllers PLC

Microcomputer based controllers and programmable logic controllers (PLC) PDT 380 : AUTOMATION IN AGRICULTURAL SYSTEMS

What is a microcomputer? • Microcomputer (μC) = microprocessor-based computer • Microprocessor (μP) = single-chip or chipset CPU

Microcomputer based controllers • 1. Microprocessor It is a digital integrated circuit which carries out necessary digital functions to process the information obtained from measurement system. • 2. Microcomputer It uses microprocessor as its central processing unit and contains all functions of a computer. • 3. Programmable Logic Controller (PLC) It is used to control the operations of electro-mechanical devices especially in tough and hazardous industrial environments.

microcomputer • A microcomputer is a small, relatively inexpensive computer with a microprocessor as its central processing unit (CPU). It includes a microprocessor, memory, and input/output (I/O) facilities. • Microcomputers became popular in the 1970 s and 80 s with the advent of increasingly powerful microprocessors. • Examples of Microcomputers are Intel 8051 controller-a single board computer, • IBM PC and Apple Macintosh computer.

General Architecture of Microcomputer System

Types of control • Temporal -- control based in time • State -- control based in state level • Hybrid – both temporal and state

Schematic of microcontroller

Programmable logic controller (PLC) • Implements logic control functions by means of a program

Industrial PLC

PLC vs PC PC PLC Optimized for calculation and display tasks Designed for (logic) control and regulation tasks Programmed by specialists Programmed by non-specialists Well adapted to industrial environment

ADVANTAGES OF PLC • Less wiring. • Wiring between devices and relay contacts are done in the PLC program. • Easier and faster to make changes. • Troubleshooting aids make programming easier and reduce downtime. • Reliable components make these likely to operate for years before failure • They are cost-effective • They are flexible, reliable and compact • They have significant advantages over traditional control systems based on relay or pneumatics

Disadvantages of PLC • PLC were Designed for Relay Logic Ladder and have Difficulty with some Smart Devices. • To maximize PLC performance and Flexibility, a number of Optional Modules must be added

COMPONENTS OF A PLC processes the information collected from measurement system takes logical decisions based on the information sends this information to actuators or output devices. Stores: a. the input data collected from sensors b. the programs to process the information and to take necessary decisions or actions. used to communicate with the outside world/operator.

Local Area Network (LAN) Serial communication PLC COMMUNICATION Common standards