Transcript Diapositiva 1

AUTOMATED SYSTEMS
1st lesson 4^ ELT A
Linear systems
Multimedia technicians:
Lorenzo Bianchini
Paolo G. De Maio
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
Automated processes
are regulated by time
but, as you know
sometimes we will work
inside frequency domain
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
System theory
The birth of a mathematical theory capable of analyzing complex
systems allowed the field of research to be extended to natural
systems
•Biological systems
•Economic systems
•Physics sistems
•Social systems
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
What is a system?
A portion of reality whose behavior can be described by the evolution
along the time of a set of variable quantities (called output)
as a function of a set quantities that can be modified from the outside
(called input)
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
From 1st year lessons the following definitions
are evolved as follows:
System
a combination of components that act together to perform a function
not possible with any individual parts.
The word System is interpreted to include physical, biological,
organizational, and other entities which can be represented through a
common mathematical symbolism.
The formal name system engineering can also be assigned to this
definition of the word System.
Thus, the study of feedback control systems is essentially a study of
an important aspect of systems engineering and its application.
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
Static and dynamic systems
A system is “static” if the outputs depend only on the inputs of the
same instant.
A system is “dynamic” if the outputs depends not only on the
inputs in that very instant, but also on the past inputs, meaning the
system has a memory whose description is given by a set of
variables called “state”
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
The art of automatic control systems
permeates life in all advanced societies
today.
Such systems act as a catalyst in promoting
progress and development.
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
One of the earliest
automated systems was
Hero’s devices for opening
the doors of a Temple, the
command input was
lighting a fire upon the
altar
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
The devices was probably actuated when the Ruler and his
entourage started to ascend the Temple steps, and so time was
a fundamental variable to calculate obviously we can consider
it an open loop system.
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
Systems in which the output quantity has no effect upon the input
quantity are called “Open loop control system”
Input
Open loop
system
output
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
For example, we go to a banquet
in, say, 100 BC. A bowl of wine
sits on a center table with a spigot
above it. The guests dip wine from
the bowl. As the level drops, wine
magically begins flowing from the
spigot to refill the bowl.
Inside, hidden from view, is a balland-cock float-valve, just like the
one in your toilet. It's pure
feedback control. It senses,
compares, and corrects the liquid
level by itself, without human
intervention.
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
That sort of thing was common in the Hellenistic world.
One of the first feedback devices was the water-clock flow
regulator.
The 3rd-century BC engineer Ktsebios made the ancient waterclock into an accurate timekeeper by inventing a float stopper to
regulate a constant flow of water into the indicator tank.
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
Experience of some ancient Hellenistic engineers bore its fruit after
1800 years.
The feedback concept was right at the heart of 18th-century
revolution (not only industrial).
The concept of self-correction is what democracy is all about.
Think about this:
The concept of self-correction is what democracy is all about.
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
Closed loop implies that the action resulting from the comparison
between the output quantities and input quantities acts in order to
maintain the output at the desired value
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
James Watt’s
flyball governor
for controlling
speed, developed
in 1788, can be
considered the
first feedback
control system
not involving
human being.
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
Watt's governor was a superb
example of feedback control.
Feedback controllers,
mechanisms that sense a
discrepancy and correct it, are
absolutely shot through our world
today. We go through hardly an
hour of any day without using
feedback devices float valves in
our toilets, thermostats in our
rooms, pressure-control valves
and carburetion electronics in our
cars etc..
Water mills flow governor
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
As you know, the desired performance characteristic of a system,
may be specified, for example, in terms of the transient response to a
unit step-function input.
Last year, we studied basic mathematical tools to analyze systems in
time domain (state matrices) and in frequency, or better, complex
variable “s” (Laplace transform).
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
Industrial- process temperature- control system
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
Industrial- process temperature- control system
Ref
+
e
Temp
G
-
H
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
Industrial- process temperature- control system
G
H
G(s)
W (s) 
1  G(s) H (s)
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
In general terms:
Open loop:
•Faster
•requires perfect knowledge about the system
Closed loop:
•Slower
•can deal with a wide class of problems
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
In the next two years, while deepening the study of
control systems in analog domain, we’ll discover
that the two previous sentences are not completely true.
The closed loop can cause problems of system
instability.
We will spend many lessons in analyzing
these phenomena in Time or Frequency domain.
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine
Ing. Rodolfo Malacrea I.T.I. Malignani - Udine