1. Programmable Logic Controllers
A Concise Exploration

2. I. Industrial Automation
Common knowledge: computers are used in factories...
Robotic arm, CNC, injection molding

3. I. Industrial Automation
Donut machine, Ice cream sandwich machines

4. 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...

5. I. Industrial Automation
Why should you care? Because you will run into PLCs...
Did you know? <Insert shocking Buckley statistic here>
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.

6. 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…

7. 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.

8. II. History
Machines become autonomous.
Common method: relay logic

9. 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.

10. 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)

11. 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 load’s coil

12. IV. Ladder Logic Simple “always on” load:
Boring... Load controlled by a single contact:
[Switch_Con = Switch]

13. IV. Ladder Logic
Boolean logic - C = A and B
C = A or B

14. 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

15. 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)]

16. IV. Ladder Logic
Converting between ladder logic and physical electronics is straight forward.
So this…

17. IV. Ladder Logic
…becomes this:

18. 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

19. 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:

20. V. PLC
Hello World on the PLC. Real hardware:
In ladder logic:

21. 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.

22. 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.

23. 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)

24. 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.

25. V. PLC
Timer:
Counter:

26. VI. Washing Machine Washing machine example, using sequencer. Steps:
0. Fill with hot water -pump, hot water valve
5. “Agitate” and drain - spin motor, agitate motor, drain valve
1. “Agitate” – spin motor, agitate motor
6. Fill with cold water -pump
2. “Agitate” and drain – spin motor, agitate motor, drain valve
7. Spin and drain –spin motor, drain valve
3. Fill with hot water -pump, hot water valve
8. Stop
4. “Agitate” - spin motor, agitate motor

27. VI. Washing Machine Reorganize into the “outputs”: edit the I/O Table
Assignment – complete the program – due 2/27
Output
Active in steps…
Pump
0, 3, and 6
Hot water valve
0 and 3
Spin Motor
1, 2, 4, 5, and 7
Agitate Motor
1, 2, 4, and 5
Drain valve
2, 5, and 7

28. I/O Table – 1st step

29. 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.

30. 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 Seq1:0 to reset the sequencer by defining an output FUNC

31. 60 on / 40 off

32. 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

33. VII. …
References
- Old relay logic
- Donut machine
- Homer Price
- Krispie Kreme
– Ice Cream Sandwiches
– DVD Boxes
– Plasma Cutting
– Injection Molding
-- Injection Molding
-- Injection Molding