Programmable logic controllers

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  • 1895 paper to ASME
  • He told of a new brewery built in Florida with a capacity of 1,300,000 barrels a year. The same-size brewery in Milwaukee turning out the same amount of barrels employed 586 men. The new plant hires 107 men. That's less than one-fifth, which means that 80 percent of brewery labor will go jobless as new plants go into operation.

Transcript

  • 1. Basics of PLC Programming EE 100 – Intro to EE Fall 2004 Dr. Stephen Williams, P.E.
  • 2. Overview How did we get where we are today? How does a project at GM in 1968 relate to the work of Henry Leland in the late 1800s? PLC SLC AB Autos GM Ford Bus Sensor Drive
  • 3. Vocabulary Programmable Logic Controllers  Definite-purpose computers design to control industrial processes and machines Drives  Solid-state devices designed to control motors Sensors  Transducers used to obtain information
  • 4. First Programmable Controller General Motors Corporation  Hydromatic Division Replacedrelay-controlled system PDP-8 minicomputers? MODICON 084  Modular Digital Controller
  • 5. Information Flow
  • 6. Genesis of Automation Operation sheets  May date back to the 1830s Listing of:  All machining operations  The machine tools employed  Tools, jigs, fixtures, and gauges Organization and flow of work
  • 7. Industrial Revolution High-volume production Interchangeable parts Transportation system Inexpensive energy (coal) Frederick W. Taylor  Scientific management Henry Ford
  • 8. Purpose of Automation Increase productivity Standardize components or processes Free workers from repetitive, and sometime dangerous, tasks
  • 9. Early Automation Applications 1869 – Refineries in Pennsylvania automatically covert crude oil to kerosene 1937 – Pictured is the loading and unloading of stators via an overhead conveyor for dipping in continuous process oven
  • 10. The Case Against Automation Las Vegas Sun, August 2, 1961  Jimmy Hoffa saw a new industrial revolution forming with automation being a threat to his giant union more menacing than the Justice Department, Attorney General Bobby Kennedy and the president himself.  He felt he could cope with the Senate committees, the FBI, and all the new legislation being written, which he thinks is aimed at unionism. It is with automation that all his talents, energy and ability must be directed.
  • 11. Forces Driving Automation Lower costs Faster production Better quality control How have they remained relevant today?
  • 12. Engineering Resources Why do you need all of these engineers running around to make all of this stuff work?
  • 13. Breakthroughs and Plateaus Where have we seen breakthroughs, and then plateaus of technology?  Microprocessors  Graphical User Interfaces  Power Electronics  Software Systems
  • 14. Brief Review of Technology Traditional (ancient?) devices  Still used in many plants  If it ain’t broke … Where are we going?
  • 15. Traditional Relay Logic Used since … Control via a series of relay contacts On and off inputs Race conditions on the outputs Very expensive  Hard to design and construct  Difficult to maintain
  • 16. Traditional Devices Relays Contactors Motor Starters Manually operated switches Mechanically operated switches Electrically operated switches
  • 17. Relays Original control elements Now used as auxiliary devices  The PLC is not designed to switch high currents or voltages CR1-1 CR1
  • 18. Contactors Used for heavy-duty switching Provides isolation from high voltages and large currents Usefully for large inductive currents, such as motor starting
  • 19. Motor Starters Contactors + Overload Relay Overload relays were usually heaters and bimetal strips  The bimetal strip separates when heated Next steps:  PLCs and motor starters  Electronic overloads  Intelligent starters
  • 20. Manually Operated Switches Pushbuttons  Normally open  Normally closed  Break-then-make  Make-then-break Selector switches  Maintained or spring return
  • 21. Mechanically OperatedSwitches LimitSwitches Temperature Switches Pressure Switches Level Switches
  • 22. Electrically Operated Switches PhotoelectricSwitches Proximity Switches
  • 23. Whats ahead? Solid state devices to replace motor starters Distributed smart sensors Micro- and nanomachines Adaptive control Smart maintenance
  • 24. SummaryA very brief history of industrial automation Overview of some of the older technologies Some thoughts on the future
  • 25. PLC Systems CPU  Processor  Memory  One Module  Power Supply  Part of the chassis or a separate module Programming/ Monitoring Device I/0 Modules
  • 26. Small Logic Controllers
  • 27. Input and Output Input Modules  Convert “real world” signal to PLC input  24 V, 120 V, Analog, etc. Output Modules  Convert PLC signal to “real world” output  24 V, 120 V, Analog, etc. Limiting values  PLC power supply
  • 28. Configurations Fixed I/O  Limited expandability Rack  Many modules, with the possibility of chaining many racks together SLC 500 is a fixed I/O device SLC 5/02 uses a rack configuration
  • 29. Chassis Versus Rack One “Rack” is 128 inputs/outputs A chassis is the outer shell of the PLC Chassis ≠ Rack SLC 5/02’s in S-340 have a ten-slot chassis  Slots are numbered from 0 to 9
  • 30. SLC Image Tables Hex numbering Addressing  I1:2.0/01 I is for the file type  1 is the file number  2 is the element number  .0 is the sub-element number (>16)  /01 is the bit number
  • 31. “Real World” Address I1:3.0/01 I is the module type  1 is redundant  3 is the slot number  .0 is for terminals above 15  /01 is the terminal number
  • 32. Remote Racks I/O racks located close to the equipment being monitored Simplifies wiring Communication modules  Similar to LAN  Fiber Optic  Coaxial cable
  • 33. Discrete I/O Modules Either “on” or “off” Bit oriented Various ratings  24 V  120 V  TTL  4 – 20 mA
  • 34. Special I/O Modules Analog High speed counter Thumb-wheel TTL Encoder PID Servo
  • 35. Memory Organization Not the same on all manufactures  Allen Bradley uses two main types Memory Maps  Data table  User program  Internal registers Memory allocation could be fixed or variable
  • 36. SLC Program File StructureProgram File UseNumber0 System Functions1 Reserved2 Main Program3-255 Subroutines
  • 37. RSLogix 500 Screen Define controller attributes  Model  Memory  Communication Program files  Main program  Subprograms
  • 38. SLC Data File StructureData File UseNumber0 Output Image Table1 Input Image Table2 Status Table3 Bit Table
  • 39. SLC Data File StructureData File UseNumber4 Timer Table5 Counter Table6 Control Table7 Integer Table
  • 40. SLC Data File StructureData File UseNumber8 Reserved (Floating Point Value Table)9 Network Table10-255 Any combination of Bit, Timer, Counter, Control, or Integer Tables
  • 41. RSLogix 500 Screen Access to input and output tables Access to timer and control control files
  • 42. Address Format What type of device or module Where is it located physically or in memory For example, T4:0/DN is the done bit for timer 0 in file 4 I:2.0 is an input module in slot 2 Word versus bit addresses  I:3.0 is a word, I:3.0/04 is a bit
  • 43. Multiword Elements Timers,counters, and control elements Three words used  Control word to store status  Preset word to store desired value  Accumulated word to store present value  Control file store a length and position value (on functions other than counters and timers)
  • 44. Counter Element ExampleName Address ExampleControl Word C5:0 C5:0/DNPreset Word C5:0.PRE 5000Accumulated C5:0.ACC 1240Word
  • 45. RSLogix 500 Screen Counter C5:0
  • 46. Program Scan Each cycle through the program and I/ O process is called a scan Scan times vary with the length of the program and the speed of the processor
  • 47. Programming Environments Languages available  Ladder logic  Boolean  Function chart Ladder logic is the most common Function chart is the future C, BASIC, etc., are also possible
  • 48. Transducers Converts energy from one form to another Input transducers  Real world into the PLC Output transducers  PLC to real world
  • 49. Sensors Sensors are transducers used to measure or detect Convert mechanical, magnetic, thermal, or optical variations into electrical quantities Sensor input is the basis for most of the decisions made in a large system
  • 50. Proximity Sensors Detect the presence of a object (target) without physically touching the object Solid-state devices Completely encapsulated Used when:  Detectingsmall objects  Rapid response is required
  • 51. Inductive Proximity Sensors Senses a metallic object A change in the magnetic field occurs when a metallic object enters into range This type of sensor can “see” through cardboard boxes and other enclosures Current-sourcing or current-sinking output
  • 52. Manually Operated Switches Pushbuttons  Normally open  Normally closed  Break-then-make  Make-then-break Selector switches  Maintained or spring return
  • 53. Counter Instructions Count Up or Down Similar to timers, but without an internal source Two methods used: block and coil  SLC 5/02s use the coil format PREset and ACCumlated values RESet similar to RTO
  • 54. How Counters Work Increment or decrement on a false to true input transition They are retentive  The accumulated value remains when the rung goes false PREsetcan be changed by the program  Move a new value into C5:0.PRE
  • 55. Control Bits15 14 13 12 11 10CU CD DN OV UN UA CU = Count Up CD = Count Down DN = Done OV = Overflow, UN = Underflow
  • 56. Integer Limits PREset and ACCumulator values must be integers Integers on the SLC 5/02 range from 32,767 to -32,768 Cascade counters to go beyond these limits
  • 57. Cascading Example
  • 58. Down Counters The SLC 5/02 does not have a true down counter  The counter does not start at a value and become true when the ACCumulator is zero TheSLC 5/02 CTD works with another counter with the same address
  • 59. Down Counter Example
  • 60. Types of Data Instructions Math Functions  Add, subtract, multiply, etc. Data Conversion and Comparison  Integer to BCD, Less than, Equal, etc. Logical Operations
  • 61. Bits, Words, and FilesA bit is the smallest unit of information  T4:0/DN is a bitA “word” is another name for a register  T4:0.PRE is a wordA “file” is a block of words, also known as a table  T4 is a file
  • 62. Data Transfer – Move The move instruction takes a value from a register, or a constant value, and places it in another register
  • 63. BCD Move Into a Register Moves an integer value into a BCD device. In lab, the LED Display
  • 64. BCD Move From a Register Moves an BCD value into an integer register. In lab, the thumb-wheel inputs
  • 65. Comparisons Greater than, less than, equals, etc. When true, output is true
  • 66. Today’s Task Use what you have learned to “break the code” Each bench has a PLC program The first bench to turn on all five lamps wins!