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EET273

EET273. Electronic Control Systems Week 2. Lab 0 Recap. Good job! Learning to troubleshoot is a key part of this class/lab

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EET273

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  1. EET273 Electronic Control Systems Week 2

  2. Lab 0 Recap • Good job! • Learning to troubleshoot is a key part of this class/lab • I am happy to help, but when you ask for help, you should be prepared to list off several things you have already tried, and have specific questions about what to try next. • “It’s not working, can you help?” is not a very good question to ask.

  3. Quick Review • Control system is: • A system that uses feedback to improve the system’s performance, and ultimately produce a better output • Open-loop: no feedback • Closed-loop: with feedback • Closed-loop systems almost always perform better….but may or may not be worth the added cost or complexity • Transfer functions • A mathematical description of a system TF = Output / Input • In an opamp, the TF is simply the gain • How to combine TF’s in series – multiply the transfer functions • The TF for a basic “G & H” feedback system: TF = G / (1 + GH)

  4. Quick Review • Goal of control is to: • reduce/eliminate our error signal • Have the output track the input (reference) signal • We may want the output to track the input as close as possible, or we may want the output to lag some, depending on the application • Ex. Quick tracking: drone • Ex. Slow tracking: elevator, too quick means a jolty ride • Some definitions: • Setpoint: The target value for a control system to maintain the process variable at (input) • Process (or measured) variable: The physical quantity measured (and controlled) by an instrument system (output) • Manipulated variable: Controller output variable, this is sent to the plant from our controller

  5. Website resources • Allaboutcircuits.com  go here! • Ladder logic • Closed loop simulator: • “Intro to control systems” link on class website • http://www.facstaff.bucknell.edu/mastascu/eControlHTML/Intro/IntroWithProblems/Intro00.html

  6. Ladder Logic Diagrams

  7. Ladder Logic • Circuits are connected between 2 “rails”, and listed from top to bottom in “rungs”, resembling a ladder. • L1 – “hot” AC wire, L2 – “neutral” or grounded wire • All electrically common points are numbered with the same number (and preferably the same color wire, though not always practical) • Fuses are connected to the left rail • Ground fault to center wire causes fuse to blow • Switches are placed on the left rail of the diagram • Loads are placed on the right rail of the diagram (grounded side) • In case of a ground fault, both sides of the load are grounded

  8. Ladder Logic • Normal state of switch/relay: • Out of the box state of a switch/relay • State when no stimulus is applied, “de-energized state” • Not necessary the state the switch spends the most time in • NC flow switch that always has flow present, closed is actually the abnormal state • Parallel contacts create an OR function • Series contacts create an AND function • NC (normally closed) contacts create an INVERTER function

  9. Ladder Logic Symbols

  10. Ladder Logic Symbols – Relay Coils/Switches

  11. Ladder Logic • OR function

  12. Ladder Logic • AND function

  13. Ladder Logic • Inverter function

  14. Ladder Logic • NAND function

  15. Ladder Logic • NOR function

  16. Ladder Logic • XOR function

  17. Ladder Logic • Invert an output • Switch “A” activated control relay CR1 (NC), and turns off lamp

  18. Ladder Logic • Latch or “seal-in” circuit • Start button need only be pushed momentarily to “latch” the circuit on • When stop is pushed momentarily, CR1opens, and the latch is broken

  19. Ladder Logic Examples • Fire Alarm – switches in parallel – OR logic • Some configurations are better than others! – think about what happens when a circuit fails! • Better:

  20. Ladder Logic Examples • Forward/Reverse Motor Controller: Better 

  21. Ladder Logic • What’s the problem here?

  22. Ladder Logic • What’s the problem here? • CR1 and Green lamp loads are in series – what happens if there’s a ground fault? • What happens if either load shorts/opens?

  23. Intro to PLCs • Why PLCs? • Convenient alternative to relays • Instead of re-wiring a circuit, just load a new PLC program • May be programmed using a ladder logic diagram • Makes existing hardware more versatile: • Have a NO switch, but need a NC switch? Just switch the behavior of X1 in the PLC • “Virtual switches” in the PLC allow a physical switch to used multiple times in different rungs of the PLC ladder logic • Real-time remote monitoring and control via software

  24. PLC Intro • Example: referencing the same physical switch multiple times • Y1 turns on if at least 2 of the pushbuttons X1,X2,X3 are turned on • Using relays, this would mean adding another physical relay for each instance of a switch • In a PLC, it’s just bits in memory!

  25. PLC Wiring

  26. Lab 1 • Wiring Lab – need to accurately wire a complex system • Need to have your spade connectors! • Lab will be graded based on quality of wiring • Use of correct colors for power/ground • All wiring ran inside of the trainer box where possible

  27. Next Week: • HW 1 is due • Quiz 1 – will be very reflective of the HW

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