Electronic Control Systems Week 2 EET273 Electronic Control Systems Week 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.

Quick Review Control system is: Transfer functions 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)

Quick Review Goal of control is to: Some definitions: 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

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/IntroWithPr oblems/Intro00.html

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

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

Ladder Logic Symbols

Ladder Logic OR function

Ladder Logic AND function

Ladder Logic Inverter function

Ladder Logic NAND function

Ladder Logic NOR function

Ladder Logic XOR function

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

Ladder Logic Latch or “seal-in” circuit Start button need only be pushed momentarily to “latch” the circuit on When stop is pushed momentarily, CR1 opens, and the latch is broken

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

Ladder Logic Examples Forward/Reverse Motor Controller: Better 

Ladder Logic What’s the problem here?

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?

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

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!

PLC Wiring

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

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