1. PLC’s programmable logic Control
Chris McAllister
11/14/12

2. What is a PLC?

3. Overview
Processes I/O signals using simple logic instructions to monitor and control devices and machinery
Five basic components
Processor
Memory unit
Power supply
I/O module
Programming device
Operating Cycle
Input Scan
Program Scan
Output Scan

4. Where it’s used Assembly Lines Machinery Water Treatment Plants
Ventilation Systems
Car Washes
Roller Coasters
Elevators

5. Example Australian Mining Industry
Precise control, immunity to electrical noise, real time system, continuous monitoring
One PLC runs multiple machines, quicker testing, less space, flexibility

6. Types of PLC’s Unitary Modular Rack Mounting Simplest and cheapest
Used in industries that rarely change production techniques
Modular
Adaptive/multifunctional
Rack Mounting
Same as modular just more compact
Most expensive

7. Primary Vendors Siemens Allen Bradley Modicon Mitsubishi Omron Koyo
Baldor

8. Costs Depends on number/type of inputs and outputs PLC processor speed
Software
Brand

9. Costs Unitary Modular Rack Module components Starting at $125
Discrete I/O $41
Analog I/O $55
Communication and networking $100
Speciality modules $197
Software $395

10. Supporting Technology
Sensors, Timers, Actuators
Network Communications
RS-232, RS-485, Ethernet, Field bus
Software/programming

11. Application Rules and Limitations
Can only respond as fast as input and output devices can send and receive data
During scan cycle the input value can change immediately after it is sampled and the program will use the old input value to determine output values
This is only a problem in processes that are very fast and hazards can occur during the scan times

12. Existing Standards
PLC programming standards published by the International Electrotechnical Commission in 1992 (IEC )
Five languages: Ladder logic diagram, function block diagram, sequential function chart, instruction list, and structured text
All languages have to be able to interact with each other

13. Technical Paper
Title: Programmable logic controllers find a home in wastewater treatment
Authors: Harold D. Gilman and Francis P. Thompson
Source:

14. Technical Paper
PLC’s used in waste water treatment because they can hold up in the dirty environment
Fast reliable control
Computers can be networked to PLC’s for monitoring
Safety control systems

15. Class Application
Are the ladder logic images below for an AND, NOT, NAND or an OR gate?

16. Summary
PLC’s are used everywhere for controlling electromechanical devices and machinery
There are five PLC languages defined by IEC
The operating cycle of a PLC consists of an input scan, program scan, and output scan

17. References http://www.youtube.com/watch?v=23Xsrbg8gAA