1. Electronic Control Systems Week 2
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: 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)

4. 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

5. Website resources Allaboutcircuits.com  go here!
Ladder logic
Closed loop simulator:
“Intro to control systems” link on class website
oblems/Intro00.html

6. 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

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 Symbols

9. Ladder Logic
OR function

10. Ladder Logic
AND function

11. Ladder Logic
Inverter function

12. Ladder Logic
NAND function

13. Ladder Logic
NOR function

14. Ladder Logic
XOR function

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

16. 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

17. 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:

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

19. Ladder Logic
What’s the problem here?

20. 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?

21. 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

22. 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!

23. PLC Wiring

24. 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

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