Copyright © 2007 Rockwell Automation, Inc. All rights reserved. Andres Gomez Sr. Systems Application Engineer PLC Basics An introduction to the P rogrammable L ogic C ontroller Version 1.10 Copyright © 2007 Rockwell Automation, Inc. All rights reserved. 2 PLC Basics Agenda 1. Introduction to Terms / Concepts 1. Introduction to Terms / Concepts 4. Basic Selection criteria and Applications 4. Basic Selection criteria and Applications 2. Programming a PLC 2. Programming a PLC 3. Application Example 3. Application Example 5. Hands-On Lab 5. Hands-On Lab Copyright © 2007 Rockwell Automation, Inc. All rights reserved. 3 How did the “PLC” get started? • 1960 -> GM (Hydramatic Division) approached suppliers to help with a problem: – Relay “walls” covered the plant floor. – Changes and Troubleshooting took weeks/months. High costs – Every change (model year) was major destruction and re-wiring. 9 Allen-Bradley PLC 9 9 Allen Allen - - Bradley PLC Bradley PLC GM needed the flexibility of “solid state”; a controller that could be programmed and maintained by plant engineers; and was rugged enough to withstand the factory environment and provided easy troubleshooting . GM needed the flexibility of GM needed the flexibility of “ “ solid state solid state ” ” ; a controller that could be ; a controller that could be programmed and maintained by plant engineers; and was rugged programmed and maintained by plant engineers; and was rugged enough to withstand the factory environment and provided easy enough to withstand the factory environment and provided easy troubleshooting . troubleshooting . Copyright © 2007 Rockwell Automation, Inc. All rights reserved. 4 PLC (Programmable Logic Controller) Inputs Output Devices C R What is a PLC ? • A solid state (electronic) device that controls output devices based on input signals and a user developed program. • Originally developed to directly replace relays used for discrete control. Copyright © 2007 Rockwell Automation, Inc. All rights reserved. 5 Two types of I/O (Inputs & Outputs) 1 0 4095 0 • Analog • Has many possible states between two values. • Example: Temperature sensor. • Range of values between two limits. For example: • 0°F represented by “0” • 100°F represented by “4095” (example) • Electrically: 4-20mA, 0-5VDC, -10 to 10VDC • Digital • Also called Discrete • Has two possible states • Represented by “1” or “0” • Electrically: • “0” is usually 0 Volts (AC or DC) • “1” is a fixed voltage value such as 5VDC, 24VDC, 120VAC, etc. • Technology: Relays, Triac, Transistor, MOSFET, TTL Copyright © 2007 Rockwell Automation, Inc. All rights reserved. 6 Electrical Characteristics of I/O Digital (Discrete): • AC or DC voltage: – 240 VAC – 85-120 VAC/VDC – 24 VAC/VDC – 120/230 VAC – 24 VDC – 5V – and more . • Technology: – Relays – Triac – Transistor MOSFET – TTL Analog: • Current or Voltage – 0-20ma – 4-20mA – 0-10VDC – 0-5VDC – -10 to 10VDC – etc. Copyright © 2007 Rockwell Automation, Inc. All rights reserved. 7 Type of Device • Pushbuttons (Discrete) • Selector Switches (Discrete) • Motor Starter Contacts (Discrete) • Relay Contacts (Discrete) • Thumbwheel Switches (Discrete) • Limit Switches (Discrete or Analog) • Level Switches (Discrete or Analog) • Photoelectric Sensors (Discrete or Analog) • Proximity Sensors (Discrete or Analog) • Temperature Sensors (Discrete or Analog) What are “typical” Input devices for PLC’s? Device Ratings Discrete • 120/240 VAC • 24 VDC – Sourcing – Sinking • 24 VAC Analog • 4-20mA • 0-10VDC Copyright © 2007 Rockwell Automation, Inc. All rights reserved. 8 What are “typical” output devices for PLC’s? Type of Device • Motor Starters (Discrete) • Solenoids (Discrete) • Control Relays (Discrete) • Buzzers (Discrete) • Lights (Discrete) • Horns (Discrete) • Fans (Discrete or Analog) • Valves (Discrete or Analog) • Heaters (Discrete or Analog) Device Ratings Discrete • Relays – 240 VAC – 85-120 VAC/VDC – 24 VAC/VDC • Triac – 120/230 VAC • Transistor MOSFET – 24 VDC Analog • 4-20mA • 0-10VDC Copyright © 2007 Rockwell Automation, Inc. All rights reserved. 9 CR Isolation Barrier Isolation Barrier MEMORY program data High Voltage High Voltage Low Voltage AC Power Supply 85-264 VAC, 50/60Hz O u t p u t C i r c u i t s External DC Power Supply or RS-232 Communications I n p u t C i r c u i t s Central Processor (CPU) What's really inside a PLC? Copyright © 2007 Rockwell Automation, Inc. All rights reserved. 10 General PLC Concept • PLC performs relay equivalent functions • PLC performs ON/OFF control • Ladder diagram program representation • Designed for: – Industrial environment – Easy programming – Easy troubleshooting – Easy maintenance • Quick to install • Adaptable to change G rea t l o w c o s t a l t ern a t iv e t o m u ltip l e i n d i v i du a l re l a ys , t i m ers an d co u n t ers a s w el l as d e d ic a t ed s in g l e b o a rd co n tro ll er s . . engineers; and was rugged programmed and maintained by plant engineers; and was rugged enough to withstand the factory environment and provided easy enough to. programmed and maintained by plant engineers; and was rugged enough to withstand the factory environment and provided easy troubleshooting . GM needed the flexibility