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 tory_of_the_PLC.htm tory_of_the_PLC.htm storyOfControl/Vanessa_Alfred_report.pdf storyOfControl/Vanessa_Alfred_report.pdf
Block Diagram
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 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 Decimal patternBinary numbers
Transisters and Gates
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 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