1. Copyright © 2002 Delmar Thomson Learning Chapter 1 Welcome to the World of Programmable Logic Controllers

2. Copyright © 2002 Delmar Thomson Learning Objectives Define PLC. Explain where the PLC came from. Explain why their use is valuable. Explain where they are used. Detail what PLCs can do. Explain how PLCs know what they are supposed to do.

3. Copyright © 2002 Delmar Thomson Learning What Is a Programmable Controller? A programmable logic controller, usually called a PLC or programmable controller, is a solid state, digital, industrial computer. Simply, a programmable controller is a computer, much like a desktop personal computer. A PLC is an industrially hardened computer.

4. Copyright © 2002 Delmar Thomson Learning Where Did the PLC Come From? In the 1960s, electromechanical relays, timers, counters, sequencers were the standard. Many control panels contained hundreds of these devices and a mile or more of wire.

5. Copyright © 2002 Delmar Thomson Learning Where Did the PLC Come From? (cont’d.) Reliability was low and maintenance costs high. Cost was high to modify or upgrade control panels. In 1968 the General Motors Hydramatic division specified a device that would become what we know today as the programmable logic controller.

6. Copyright © 2002 Delmar Thomson Learning Early PLCs Only relay replacers Did not have timers or counters No sequencer instructions No math instructions No data manipulation instructions

7. Copyright © 2002 Delmar Thomson Learning Why a PLC? Easily changeable Programmable Reliable Smaller Fast switching

8. Copyright © 2002 Delmar Thomson Learning Why a PLC? (cont’d.) Able to withstand harsh factory environment Consumes less power Easier to troubleshoot Easy to install

9. Copyright © 2002 Delmar Thomson Learning Why Use A PLC? The question “why use a PLC?” should really be rephrased to “why automate?” The PLC is the tool that provides the control for the automated process.

10. Copyright © 2002 Delmar Thomson Learning Automating Helps a Manufacturing Facility: Gain complete control of the manufacturing process. Achieve consistency. Improve quality and accuracy. Work in difficult or hazardous environments. Increase productivity.

11. Copyright © 2002 Delmar Thomson Learning Automating Helps a Manufacturing Facility: (cont’d.) Shorten lead time to market. Lower cost of quality, scrap, and rework. Offer greater product variety. Allow a quick changeover from one product to another. Control inventory.

12. Copyright © 2002 Delmar Thomson Learning A PLC upon First Glance A black box with wires bringing signals in and other wires sending signals out Some sort of magic being done inside that somehow decides when field devices should be turned on or off

13. Copyright © 2002 Delmar Thomson Learning Actually There Is No Magic The PLC is a computer and someone had to tell it what to do. The PLC knows what to do through a program that was developed and entered into its memory. Without a set of instructions telling the PLC what to do, it is nothing more than a box full of electronic components.

14. Copyright © 2002 Delmar Thomson Learning What Makes a PLC Work? The heart of any computer is the microprocessor. The microprocessor, also called the processor or central processing unit (CPU), supervises system control through the user program.

15. Copyright © 2002 Delmar Thomson Learning What Makes a PLC Work? (cont’d.) The processor reads input signals and follows the instructions that the programmer has stored in the PLC’s memory.

16. Copyright © 2002 Delmar Thomson Learning What Makes a PLC Work? (cont’d.) As a result of the solved program, the PLC writes information to outputs, or field controlled devices, to turn them on or off. When the PLC is running and following the programs instructions, this is called solving the user program. The PLC is running or in RUN MODE.

17. Copyright © 2002 Delmar Thomson Learning What Makes a PLC Work? (cont’d.) The user program (ladder program) is the list of instructions that tells the PLC what to do. The library of instructions available to the PLC is called the instruction set. The instruction set determines how much flexibility the programmer has.

18. Copyright © 2002 Delmar Thomson Learning Common PLC Inputs Push buttons Selector switches Limit switches and level switches Proximity sensors Photo switches Relay contacts Motor starter contacts

19. Copyright © 2002 Delmar Thomson Learning An Overview of a PLC System

20. Copyright © 2002 Delmar Thomson Learning An Overview of a PLC System (cont’d.) Incoming signals, or inputs, interact with instructions in the user program to help the PLC to determine when an input instruction is either true or false.

21. Copyright © 2002 Delmar Thomson Learning Conventional Circuit

22. Copyright © 2002 Delmar Thomson Learning Representation of a PLC Program

23. Copyright © 2002 Delmar Thomson Learning PLC Ladder Program Rung

24. Copyright © 2002 Delmar Thomson Learning Series 90-30 and 90-20 Handheld Programmer Image courtesy of GE Fanuc Automation

25. Copyright © 2002 Delmar Thomson Learning Interfacing a PC to an Omron CQM 1 PLC Image courtesy of Omron Electronics, Inc.

26. Copyright © 2002 Delmar Thomson Learning Correlating Ladder Program Rung to Actual PLC Wiring

27. Copyright © 2002 Delmar Thomson Learning Programmable Controller Block Diagram

28. Copyright © 2002 Delmar Thomson Learning Product Sensed in Position Will Send an Input Signal

29. Copyright © 2002 Delmar Thomson Learning Allen-Bradley SLC 500 Fixed PLC Image courtesy of Allen-Bradley, a Rockwell Automation business

30. Copyright © 2002 Delmar Thomson Learning Allen-Bradley SLC 500 Modular PLC Image courtesy of Allen-Bradley, a Rockwell Automation business

31. Copyright © 2002 Delmar Thomson Learning SLC 500 Power Supply and a Four-slot Rack Image courtesy of Allen-Bradley, a Rockwell Automation business

32. Copyright © 2002 Delmar Thomson Learning Installation of an I/O Module Image courtesy of Allen-Bradley, a Rockwell Automation business

33. Copyright © 2002 Delmar Thomson Learning Allen-Bradley SLC 500 Modular Processor Image courtesy of Allen-Bradley, a Rockwell Automation business

34. Copyright © 2002 Delmar Thomson Learning Limit Switch Interface

35. Copyright © 2002 Delmar Thomson Learning Output Module Wiring to a Motor Starter Coil