1. The Programmable Logic Controller

2. Basic Principle of a PLC
Program
Input Data
Processing
Output Data

3. Components of a PLC A PLC is made up of two basic sections
Central Processing Unit (CPU)
Input/Output (I/O) Interface
CPU consists of three main parts
Processor
Memory
Power Supply

4. PLC System Components PLC - Program Input Module Central Processing
Unit
Output Module
Sensors
Actuators

5. Functions of a CPU Reads input data from various sensing devices
Executes the stored user program from memory
Sends appropriate output commands to control devices

6. Types of Memory

7. Input and Output System
Provides the physical connection between the outside world and the CPU
Discrete inputs/outputs are the most commonly used

8. Input Devices Selector switches Push buttons Limit switches
Circuit breakers
Level switches
Relay contacts
Motor starter contacts

9. Input Identification Input Word IW0 - IW2
Input Bit I0.0, I0.1, …, I0.7
Input Bit I1.0, I1.1, … I1.7
Input Bit I2.0, I2.1, …, I2.7

10. Output Devices Alarms Control Relays Solenoids Lights Horns Valves
Motor Starters

11. Output Identification
Output Word OW0 - OW1
Output Bit O0.0, O0.1, …, O0.7
Output Bit O1.0, O1.1, … O1.7

12. Flag Identification Flags are Internal Relays Flag Word FW0 - FW255
Flag Bit F0.0, F0.1, …, F0.15
Flag Bit F255.0, F255.1, … F255.15

13. Timer Identification
Timers are Internal PLC Timers
Timer T0 - T15

14. System Unit of a PLC Programming Device Program Memory
Acknowle-dgements (Sensors)
Control Elements (Switches)
Central Control Unit
(Single or Multibit Processor)
Input Modules
(Input Cards)
Output Modules
(Output Cards)
Final Control Elements (Relays, Solenoids, Indicators)
PLC
Software
Sensoric
Processoric
Actoric

15. Selecting a PLC Number of Inputs and Outputs
Types of Software Languages
Types of Operator Interface
Mathematical Calculations
Analog Input and Output
Communication with other PLCs and Computers
Ease of Maintenance
Ease of Programming