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Programmable Logic Controller

Programmable Logic Controller

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Programmable Logic Controller

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  1. Programmable Logic Controller Chris Egbert Dec 1, 2008

  2. Current State • A PLC is a small, self-contained digital computer • Real time (output of the PLC is produced within a specific time bound relative to input data) • Encased in protective housing to allay extreme environmental conditions • Have multiple ports for inputs and outputs (more ports = greater cost) • Connect to sensors, actuators, and other output devices

  3. Current State (continued) • May come in a modular form, such that additional I/O modules may be attached • Programmed directly through the PLC via buttons and lights, text displays, GUIs, or through a connected PC with appropriate software • Utilize networks for communication

  4. Where Used • Automation processes • Machinery on factory lines • Machining, electronics assembly, etc • Control of amusement park rides • Control of lighting fixtures • Interpretation of any type of sensor input

  5. Uses • Who: • Automated factories • Amusement parks • Any type of control system (could be used for a small device that responds to inputs) • What for: • Factory control (machines, conveyors, storage retrieval, etc) • Device response control • Force regulation on park rides • Many more

  6. Uses (continued) • When: • Whenever automation is required or human skill is not great enough to operate a machine • Whenever great precision is required • Under difficult environmental circumstances

  7. Costs • ~ $50 to $5,000 • Cost depends on the number and type of inputs and outputs, PLC processor speed, modularity of the PLC • Additional costs for additional I/O modules • Economic for situations in which production quantities are not very large as to allow a custom-designed control

  8. Supporting Technology • Communications • RS-232, RS-485, Ethernet, coaxial • Personal Computer for software editing • Programming Languages: • FBD (Function block diagram) • LD (Ladder diagram) • ST (Structured text, similar to the Pascal programming language) • IL (Instruction list, similar to assembly language) • SFC (Sequential function chart) • Adequate Sensors

  9. References • http://www.allaboutcircuits.com/vol_4/chpt_6/6.html • http://www.omron.com/products/indu.html • http://www.eod.gvsu.edu/~jackh/books/plcs/chapters/plc_intro.pdf • http://www.jlab.org/accel/ssg/Pss/plc.pdf • http://www.eod.gvsu.edu/~jackh/books/plcs/html/plcs.html#pgfId-864358

  10. Application Rules and Limitations • Useful in situations that require output responses to given inputs • Can only respond as fast as input and output devices can send and receive data • Though rugged, still limited by operating environment (i.e. 0 to 50 deg C, 10-90% humidity, 2000m or less altitude, etc)

  11. Vendors

  12. Standards • IEC 61131-3 • Defines 5 standards-based programming languages (listed earlier)

  13. Technical Paper • Title: • Multi-axes sun-tracking system with PLC control for photovoltaic panels in Turkey. • Authors: • Sungur, Cemil1 • Source: • Renewable Energy: An International Journal; Apr2009, Vol. 34 Issue 4, p1119-1125, 7p • A solar panel, attached to an electromechanical system and controlled by a PLC, is oriented to follow the sun’s position over a year so as to attain greatest solar energy input

  14. Integration • Principles of automation are based upon control systems • Automation breaks down if it cannot respond to variation, which is unavoidable • PLC’s act as the brains of the control system, interpreting real time data to alter the way the system operates

  15. Video • http://video.google.com/videosearch?q=PLC&emb=0&aq=f#q=christmas%20light%20music&emb=0

  16. Class Application • A device must determine temperature, speed, acceleration, and pressure. The device must then take this data and adjust to follow a user defined speed and acceleration (through the use of 2 stepper motors). If a PLC were used to control this system, how many inputs and outputs would it need?

  17. Summary • Modern automation is built upon the backs of PLC’s • PLC’s are highly customizable and may be altered to achieve a variety of tasks • PLC’s are an inexpensive alternative to highly specialized control systems • PLC’s require user defined programming in order to properly adjust for given inputs • As processing capability has increased with time, so too has the ability of PLC’s to perform an even wider range of tasks • A PLC may only be as fast and accurate as the sensor inputs