1. CHAPTER - INTRODUCTION TO PLCS
Advantages of PLCs
Cost effective for controlling complex systems.
Flexible and can be reapplied to control other systems quickly and easily.
Computational abilities allow more sophisticated control.
Trouble shooting aids make programming easier and reduce downtime.
Reliable components make these likely to operate for years before failure.

2. PLC Origin
- Developed to replace relays in the late 1960s
- Costs dropped and became popular by 1980s
- Now used in many industrial designs

3. Relays and
Schematic
Symbols

4. Logical Control
with Relays

5. Relay Logic
In a PLC

6. Reading Ladder Logic

7. PLC in a Control Loop

8. The Four Stages of a PLC Scan

9. Sample Problem:
Try to develop (without looking at the solution) a relay based controller that will allow three switches in a room to control a single light.