Programmable Logic Controllers

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Programmable Logic Controllers

• A Concise Exploration

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I. Industrial Automation

• Common knowledge computers are used in
  factories...
• Robotic arm, CNC, injection molding

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I. Industrial Automation

• Donut machine, Ice cream sandwich machines

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I. Industrial Automation

• Not common knowledge today this is usually
  accomplished with Programmable Logic Controllers
  (PLCs)
• PLCs are the answer to a variety of needs
  durability, reliability, flexibility,
  scalability, reprogrammability, etc...

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I. Industrial Automation

• Why should you care? Because you will run into
  PLCs...
• Did you know? ltInsert shocking Buckley statistic
  heregt
• Median starting salary for entry-level
  Electrical Controls Engineer is 57,452. (EE is
  55K, HW Eng is 48K, SW Eng is 53K)
  monster.com
• As long as there is industry, it will be computer
  controlled and engineers will earn paychecks.

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II. History

• Relentless trend toward tools in industry.
• ? Handicraft (forever)
• ? Water-powered silk mill (1721)
• ? Spinning Jenny (1764)
• Steam power (1780s)
• Gas lighting (1810s)
• Etc

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II. History

• Obvious next step Electricity
• Aside why was Buffalo the place to be 100 years
  ago? ... Hydroelectric power! started circa
  1853
• Electric tools, but still micromanaged by humans.

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II. History

• Machines become autonomous.
• Common method relay logic

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III. Relay Logic

• Conditional logic can be represented in terms of
  contacts and coils.
• Contact A simple input switch.
• Coil An output load, e.g., a relay or motor.
• Symbolic representation called ladder logic.

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III. Relay Logic

• To clarify Ladder Logic is a notation
  originally used to describe/document relay logic
  configurations.
• Later became the basis for PLC programming
  languages
• (This parallels HW Desc. Langs. (HDLs)... VHDL
  was intended by DoD to document ASICs... Learn
  more in CSE 341 and especially CSE 490)

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IV. Ladder Logic

• Power supply rails drawn as parallel vertical
  lines on left and right
• Connection of rails implies current will flow
• An output is on when a connection is completed
  and current flows through the loads coil

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IV. Ladder Logic

• Simple always on load
• Always_On 1
• Boring... Load controlled by a single contact
• Switch_Con Switch

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IV. Ladder Logic

• Boolean logic - C A and B
• C A or B

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IV. Ladder Logic

• C not A
• A contact with a slash through it is normally
  closed. This indicates a connection when A is
  NOT triggered.
• So when sensor/input A is activated, there is an
  open circuit

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IV. Ladder Logic

• Each rung of the ladder is a statement that is
  asynchronous when implemented in relay logic, but
  evaluated sequentially by the PLC.
• X (A or B) and (C or D),
• Y A and B or (C and D)

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IV. Ladder Logic

• Converting between ladder logic and physical
  electronics is straight forward.
• So this

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IV. Ladder Logic

• becomes this

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V. PLC

• The first PLC was invented by Dick Morely in
  1978.
• Morely designed a computer with three components
  a processor, memory, and a logic solver.
• The logic solver allowed us to get the speed
  we needed in this application-specific computer
  to solve the perceptually simple problem of
  several cabinets full of relay wiring. -Morely

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V. PLC

• The first PLC (the 084) was extremely durable and
  reliable...
• We used to test the programmable controllers
  with a Tesla coil that struck a quarter inch to
  half-inch arch anywhere on the system, and the
  programmable controller still had to continue to
  run. Morely
• FYI, this is a Tesla coil http//www.youtube.com/
  watch?voNrgXtCu4aU

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V. PLC

• Hello World on the PLC. Real hardware
• In ladder logic

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V. PLC

• Not very interesting how about a stay-on
  variation? (When the switch is released, the
  light stays on)
• PLC benefit The state of an output in one rung
  may be used as a contact in another.
• In fact, there are internal utility relays
  virtual outputs that act as intermediate steps
  toward real outputs.

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V. PLC

• Latched (stay-on) Hello World
• When the switch is pressed, Neon will be active
  in the first evaluation.
• In subsequent evaluations, Neon will force
  itself to stay on.

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V. PLC

• A bit more convoluted toggling Hello World with
  a single button.
• Remember - Switch state ON OFF ON OFF
• Figure it out

Latch (Switch AND notNeon) OR (Latch AND
notNeon) Neon (Latch AND notSwitch) OR (Neon
AND Switch)
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V. PLC

• PLCs also support a range of special functions
  timers, counters, sequencers, memory
  instructions, etc
• Beyond the basics, they are non-standard and
  manufacturer-specific.

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V. PLC

• Timer
• Counter

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VI. Washing Machine

• Washing machine example, using sequencer.
• Steps

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VI. Washing Machine

• Reorganize into the outputs edit the I/O Table
• Assignment complete the program due 2/27

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I/O Table 1st step
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Exercises

• Turn 8 LEDs on and off in sequence, repeat.
• Turn a pump on for 60 seconds, then off for 40
  seconds, then repeat. Use a switch to start it
  off.

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Using a sequencer

• Define a Counter output call it Seq1
• Give it a set value 1 greater than your desired
  sequences
• e.g. if 4, then 0 thru 4 a set value of 5
• Use special bits as inputs
• Use Seq10 to reset the sequencer by defining an
  output FUNC

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60 on / 40 off
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60 on / 40 off
Latch an output (keeps it ON)
Count down TMR60 from 60 to 0
While TMR60 is counting down (not at 0) run PUMP
While TMR60 is at 0, count down TMR40
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VII.

• References
• http//en.wikipedia.org/wiki/Programmable_logic_co
  ntroller
• http//www.plcs.net/contents.shtml
• http//www.plcdev.com/plc_timeline
• http//www.barn.org/FILES/historyofplc.html
• http//www.jach.hawaii.edu/ets/mech/JCMT/carousel/
  car_eng.html - Old relay logic
• http//www.rootcompromise.org/gallery/v/blackhat/b
  h-windows-2004/bh_windows_2004_014.jpg.html -
  Donut machine
• http//www.fiona.co.jp/BOOK_JUV_PAGE/homerprice.ht
  m - Homer Price
• http//www.youtube.com/watch?vgKzJqXSPuRE -
  Krispie Kreme
• http//www.youtube.com/watch?v-kiSQx0imxs Ice
  Cream Sandwiches
• http//www.youtube.com/watch?v0PUFwwSDAWg DVD
  Boxes
• http//www.youtube.com/watch?vibc69W_N2h0
  Plasma Cutting
• http//www.youtube.com/watch?vy2mzjExWXzo
  Injection Molding
• http//rds.yahoo.com/_yltA9gnMiYBqv1FGjkBFlGjzbkF
  _yluX3oDMTBsdmIydTZhBHNlYwNwcm9mBHZ0aWQDSTAwMV83
  MA--/SIG12imesfu9/EXP1174338433/http3A//www.p
  lastic-gear-manufacturer.com/injection-molding.htm
  -- Injection Molding
• http//rds.yahoo.com/_yltA9gnMiIVqv1Fs60AJw.jzbkF
  _yluX3oDMTBsdmIydTZhBHNlYwNwcm9mBHZ0aWQDSTAwMV83
  MA--/SIG12pk1f58s/EXP1174338453/http3A//www.o
  ffshoresolutions.com/products/plastic/injectionMol
  ded.htm -- Injection Molding
• http//home.howstuffworks.com/washer.htm
• http//en.wikipedia.org/wiki/Industrial_revolution