1. Electronic Control Systems Week 1
EET273
Electronic Control Systems
Week 1

2. Overview Syllabus Lab Overview Intro to Control Homework/Quizzes/Labs
Class website
Lab Overview
Lab syllabus
Lab 0 overview
Intro to Control
Control symbols
Block diagrams
Transfer functions

3. Lab Overview
Building control circuits using CLICK PLC, and other control elements
Ok if you’ve never used a PLC, we’re just going to run basic programs
Lab 0 will include creating and running a basic PLC program and getting familiar with the Control System Trainers
Need to make your own wires! Purchase a box of spade terminals
Details are in Lab Syllabus

4. Intro to Control This class: Other control classes:
Closed loop controls
Advantages of closed loop control
How to design/tune a controller in a (mostly) non-mathematical way
Sensors, actuators, relays, etc.
Other control classes:
Very mathematical
Few real world examples
Little discussion of how control systems are actually implemented

5. Intro to Control Control is all about feedback
A system: takes an input, produces an output
A control system: takes an input, produces an output, but feeds back the output to influence the system behavior in a positive way.
Closed loop systems almost always have better performance than open loop systems
Control theory applies to wide range of different types of systems:
Electrical
Mechanical
Software algorithms
Financial models
Economics/psychology/sociology, etc.
Anything that can be considered a “system” with an input, output, and feedback mechanism

6. Intro to Control Examples of control systems:
Cruise controller in your car
Sprinkler system w/moisture sensor
Various Manufacturing processes
Water buffer tank, sensor to keep the level consistent
Robotics/Self-driving Cars/Obstacle Avoidance robots, etc.
Stock market prediction algorithm – very complex system!
Presidential Election:
19 republicans / 16 democrats
Each election cycle can be considered “feedback” to the electoral process, which parties adjust to, in order to stay relevant, and have a chance at winning the next election.

7. Intro to Control
Using feedback/control can solve many problems of an open-loop control system:
Performance:
Improve system performance by making system adjustments under varying load conditions
Stability:
Make a less stable process more stable (water buffer tank), or stabilize a process that is otherwise unstable to the point that it is useless (inverted pendulum)
Automatization:
Automatize a process that would otherwise require user monitoring/intervention

8. Control Terminology
Process Variable (PV) – output variable to be controlled
Setpoint (SP) – input to the system, desired output
Controller – module that processes output and feeds back to input
Final Control Element (FCE) – actuator that is acting on the process
Manipulated Variable (MV) or Output – Controller output variable
Open Loop – no feedback from output to input
Closed Loop – with feedback from output to input

9. Transfer Functions
Transfer functions are a mathematical representation of a linear system
TF = Output / Input of the system  include units!
For an amplifier/op-amp: TF = Vo/Vi  the gain of the op-amp
Transfer functions can be used to represent any linear system
In electronics: resistors, capacitors, inductors, linear gain elements
Some TF’s are frequency dependent, we won’t get into frequency dependent TF’s too much in the class, but know they exist!
Ex: temp sensor
1mV / 5°C  1V/1mV  20mA / 1V
Temp Sensor  Amplifier  Heater Controller

10. Control Diagram Elements
TF Block
Blocks can be linked in series and multiplied together
Adder (summer)
Used to sum input and feedback signals
Basic feedback system
G / (1 + GH)

11. Control diagram e = r – yH y = eG
y = (r – yH)G  substitute Eq. 1 into Eq. 2 to eliminate e
y = rG – yGH
y + yGH = rG
y(1 + GH) = rG
y/r = G / (1 + GH)  The transfer function of a closed loop system

12. Control diagram In an op-amp, G is very large
If G = 100,000, and H = 1/10  G / (1 + GH) = 100k / (1 + 10k) ~
If G = 1,000,000, and H = 1/10  G / (1 + GH) = 1M / (1+ 100k) ~
So long as G is very large, gain is dominated by the value of H
Good implementation of feedback can make the properties of the system much less of a factor
In the case of an opamp, the accuracy of the gain is much more dependent on the value of the resistors, not on the OL gain of the op-amp itself.
Since resistors are easier (and cheaper) to control the value of, this makes for a much better amplifier design

13. Summary
Closed-loop control can improve the performance of a system by making the output more closely match the desired output (setpoint).
Closed-loop control can make a system that is otherwise unstable and thus unusable perform in a way that is useable.
Links:
Inverted Pendulum:
Ball and plate:
PID Control:
TED Talk:
Balancing Cube: