Programming Logic Controllers

Overview - Chapter 1

PLC Use

• Machine control• Process control• Motion control• Batch control• Diagnostic• Other• Usually Multiple applications

History and Development

• 1960’s• “Five hours to find it, five minutes to fix it”

History

• Richard Morley – Modicon• First PLC• ladder logic programming

• Odo Josef Struger• Allen-Bradley

History and Development

• http://en.wikipedia.org/wiki/Programmable_logic_controller

• http://en.wikibooks.org/wiki/Introductory_PLC_Programming

• http://www.isa.org/Content/ContentGroups/News/2006/February24/History_of_the_PLC.htm

• http://www.barn.org/FILES/historyofplc.html

• http://www.control.lth.se/media/Education/DoctorateProgram/2012/HistoryOfControl/Vanessa_Alfred_report.pdf

• http://www.plcs.net/chapters/history2.htm

Block Diagram

Block Diagram

Block Diagram

Central Processing Unit

• http://en.wikipedia.org/wiki/Central_processing_unit

• A central processing unit (CPU) is the hardware that carries out the instructions of a computer program by performing the basic arithmetical, logical, and input/output operations of the system.

Memory Devices

• RAM• ROM

• ROM• Programmable ROM (PROM)• Erasable programmable ROM (EPROM or

UVEPROM)• Electrically Erasable ROM (EEPROM)

• Static RAM• Dynamic RAM

Address Decoder Unit

• Address to circuit• Binary number to path

Binary• http://www.jodyculkin.com/category/comics-2/countingbinary

Decimal pattern

Binary numbers

0 0

1 1

2 10

3 11

4 100

5 101

6 110

7 111

8 1000

9 1001

Transisters and Gates• http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html

• http://www.cs.bu.edu/~best/courses/modules/Transistors2Gates/

• http://www.cs.bu.edu/~best/courses/cs101/F95/lectures/FromGatesToAdder.html

• http://www.electronics-tutorials.ws/logic/logic_10.html

Peripheral Chips

• Buffers

• Data conversion

• Networking

• Voice

• Voice Recognition

• more

Discrete Input Modules• Discrete means enumerable, countable, not continuous

but distinct• Digital not analog• Real numbers are not discreet

• Between 1.0 and 2.0 we have 1.50. • Always a number between x and y

• Integers are discrete. No number falls between 1 and 2

• Generally • On or Off • 1 or 0• True or False• Closed or Open

Discrete Output Modules

• Set to on/off

• Set to true/false

• Set to 1/0

Analog Input/Output Devices

• Analog is a continuous signal (wave)

• Set to varying voltage levels

• Inputs converted to digital via analog to digital converter logic

• Digital to analog conversion occurs for outputs

PLC Power Supply

• Battery backup• Capacacitor allows battery exchange

Allen-Bradley Programmable Logic Controllers

• PICO• MicroLogix• Small Logix• SLC 500 Series

• LAN and WAN capabilities

• PLC-5• May have thousands of I/0 ports