2. What do we mean by Automatic Control?
• An Automatic control system is an interconnection of components forming a
system configuration that will provide a desired system response
The input signal is processed to induce an output signal, this is generally
done using powr amplification.
• The basis for analysis of a system is the foundation provided by linear system theory.
Produce a cause-and-effect relationship of
the process
An input output relation
can be deduced from the
block diagram
3. 3
What do we mean by Open Loop and Closed Loop?
• An open-loop (or feedforward) control system utilizes an actuating
device to control the process directly without using feedback.
Open loop control system
4. 4
When damp clothes are put in the dryer machine, the operator/user sets the
time for drying the clothes. This time acts as the input signal for the
dryer. Correspondingly at the end of that time, the machine stops and
clothes can be taken out.
Examples of open-loop control system
5. 5
What do we mean by Open Loop and Closed Loop?
• A closed-loop control system uses a measurement of the output and feedback of this
signal to compare it with the desired output (reference or command).
Closed loop (or feedback) control system
6. Examples of Open Loop Systems
Imagine a blind and deaf
person that needs to get her
car to 100Km/h, but she
cannot see the speedometer or
hear the engine revs. How will
she do it?
In all likelihood she will call on
experience and memory and
estimate the foot pedal position
required to reach the desired
speed.
Will you get good toast at the
end?
You have a toaster in which to
make toast, but you are deaf and
blind. You start counting from 1
to 120 seconds to toast the
bread.
Will she reach the desired
speed?
Clearly the biggest issue here
is a lack of measurement or
information. We have no
means of measuring the
output and thus no
information. Without
information we have no
mechanism for adjusting the
system input.
NO!!!
Open-loop control means no
measurement of the output
and thus the input is an
estimate. In practice the
estimate is wrong and hence
the output behaviour will not
match the target.
7. The fascinating property of feedback
Why do I need
feedback in
Engineering
systems?
The system compares the actual result with
the desired result, and thus takes action(s)
based on the difference.
simple idea but
tremendously powerful,
and in some cases
revolutionary.
The opposite of feedback control is feedforward or open loop control: i.e. devise a plan
and execute it.
make good systems
from bad components
Make a system
insensitive to
disturbances and
component variations
Stabilize an
unstable system
Create desired behaviour
Feedback implies
increased cost, can
cause instabilities,
and sensor noise
may be fed into the
system
However!!!!
8. 8
How do we represent Automatic Control Systems?
9. 9
How do we represent Automatic Control Systems?
10. 10
• Most of the cars have thermostatically controlled Air-Conditioning (AC) systems for the comfort of
the passengers.
• The block diagram depicts an AC system where the driver sets the desired interior temperature on
a dashboard panel.
• The thermostat and the AC unit corrects any deviation of the automobile cabin temperature through
the use of the temperature sensor
Measures the
temperature in
the cabin
Corrects any
deviation from
the
temperature
set by the
driver
Car temperature control system
Car
cabin
Car cabin
temperature
11. 11
Car steering control system
The driver uses the
difference between the
actual and the desired
direction of travel to
generate a controlled
adjustment of the steering
wheel
The desired course is
compared with a
measurement of the actual
course in order to generate a
measure of the error This
measurement is obtained by
visual and tactile (body
movement) feedback, as
provided by the feel of the
steering wheel by the hand
(sensor).
Car
12. 12
• Because a sailboat cannot sail directly into the wind, and traveling straight downwind is
usually slow, the shortest sailing distance is rarely a straight line.
• Thus sailboats tack upwind—the familiar zigzag course—and jibe downwind. A tactician's
decision of when to tack and where to go can determine the outcome of a race.
Control system Example - Sailboat Direction Control
13. 13
SISO and MIMO Control Systems
Control systems are also classified into these two categories, named as:
• Single Input Single Output systems. (SISO)
• Multiple Input Multiple Output systems. (MISO)
A Radio system is a typical example of a Multiple Inputs Multiple
Outputs system. A combination of Input signals is applied and
transmitted over multiple lines to produce the required
communication signals at the output.
A fan speed control is a very common example of a Single
Input Single Output system. A single input in terms of
voltage is supplied to the system which in turn results in
the fan working.
14. 14
Continuous and Discrete Time Control
System
• A continuous time
signal refers to a signal,
which is continuous in the
time domain.
• On the other hand, when a
signal is discrete in the
time domain, i.e. it can be
obtained at discrete time
intervals, it is called
a discrete time signal.
15. 15
A continuous time control system, all the signals
(including the input & output signals) are
continuous in time.
.
Continuous and Discrete Time Control
System
16. 16
A discrete time control system, all the signals of
the control system (including the input and output
signals) are discrete time signals.
Continuous and Discrete Time Control
System
18. Generic PID Control Equations
– KP: proportional gain
– KI: integral gain
– KD: derivative gain
0
( ) ( ) ( )
t
c P I D
P
D
I
de
u t K e t K e t dt K
dt
Time-domain
P
( ) ( ) ( ) ( )
I
c P D
K
U s K E s E s K sE s
s
D
I
S-domain
19. Effects of P, I & D Terms
u(s)
K(s)
r(s)
e(s)
y(s)
Plant
Controller
Set-Point Output
• Proportional Action (P)
• Integral Action (I)
• Derivative Action (D)
20. 20
Types of PID Controllers
Manufacturers of PID controllers arrange the Proportional, Integral and
Derivative modes into one of three different controller algorithms or
forms. These are called the
1. Interactive
2. Noninteractive
3. Parallel forms
Some controller manufacturers allow you to choose between different forms as
a configuration option in the controller software.
