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Unit 5. Automatic Control Theory
81
8. control surfaces
9. sensor information
10. measurement noise
11. non-measurable external
disturbances
i. дифференциальное уравнение в частных
производных
j. не поддающиеся измерению внешние воз-
мущения
k. сети Петри
5. Match to make word combinations.
1. automatic
2. mathematical
3. desired
4. sensor
5. hydraulic
6. time-changing
7. external
8. application
9. operating
k. models
l. values
m. information
n. control systems
o. domains
p. specifications
q. actuators
r. conditions
s. disturbances
6. Match the following words with their synonyms.
1. constant
2. measure
3. adjust
4. reduce
5. increase
6. undesirable
7. intervene
8. achieve
9. output
10. approximately
11. affect
12. input
t. cut
u. stable
v. attain
w. regulate
x. interfere
y. response
z. evaluate
aa. stimulus
bb. roughly
cc. influence
dd. raise
ee. unwelcome
WORD BUILDING
7. Complete the chart.
Verb
Noun
Adjective
regulation
operation
Measure
adjust
System analyses and control
82
Verb
Noun
Adjective
Action
behavior
specification
implement
digital
application
transmission
distribution
GRAMMAR FOCUS
Before reading the text, revise the grammar material (§4. NON-FINITE
VERBS, PARTICIPLES, p.139) and do the exercises.
8. Translate the sentences into Russian paying attention to the
functions of Participles.
1. Control system input is the stimulus applied to a control system from an
external source to produce a specified response from the control system.
2. In the case of the central heating unit, the control system input is the
temperature of the house as monitored by the thermostat.
3. Control system output is the actual response obtained from a control
system.
4. In the example above, the temperature dropping to a preset value on the
thermostat causes the furnace to turn on, providing heat to raise the temperature
of the house.
5. In the previous example, the actual storage tank water level, sensed by
the level transmitter, is feedback to the level controller.
6. This feedback is compared with a desired level to produce the required
control action that will position the level control as needed to maintain the desired level.
7. An automatic control system has two process variables associated with
it: a controlled variable and a manipulated variable.
8. Control system input is the stimulus applied to a control system from an
external source to produce a specified response from the control system.
9. In the previous example, the flow rate of the water supplied to the tank
is the manipulated variable.
Unit 5. Automatic Control Theory
83
9. Decide which participle to use and complete with -ed or -ing.
1. The level transmitter sends a signal represent___ the tank level to the
level control device, where it is compared to a desir___ tank level.
2. The measur___ element performs the measur___ function by sensing
and evaluating the controlled variable.
3. Control system output is the actual response obtain___ from a control
system.
4. Instrumentation provides the various indications us___ to operate a nu-
clear facility.
5. The information record___ helps the operator evaluate the current con-
dition of the system and take actions if the conditions are not as expected.
6. Process variables require___ control in a system include, but are not
limited to, flow, level, temperature, and pressure.
7. When the temperature drops to the value select____ by the occupants of
the house, the system activates to raise the temperature of the house.
SPECIALIST READING
TEXT A
A DAY WITHOUT AUTOMATIC CONTROL
First, what does automatic control do? Cruise control in the car keeps the
speed constant even when we go up a slope or face a head wind. Automatic control keeps the value of a variable constant (here the speed, but also temperature,
pressure, distance and so on in other applications) under a variety of operating
conditions, automatically. Amazingly, in the human body automatic control systems are abundant and include regulation of body temperature, of white cell concentration in the blood, of the heart pumping rate, to mention but a few.
But how important is automatic control? To show clearly what automatic control is and how important it is to us, we will try to imagine what a
day without automatic control would be like, before getting into the details of
how control works.
If there is no automatic control there is no heating or air-conditioning the
way we have become accustomed to – where certain temperature and humidity
levels are maintained. Refrigerators and stoves would not be able to regulate their
operation. Any safety device is a control device. The electric power grid maintains
System analyses and control
84
very tight control on the frequency of the AC voltage, and if that fails blackouts
occur. Automatic pilots in airplanes are automatic control systems, and helicopters
or military aircraft would not be able to fly at all without automatic controls.
Where is the magic? How does automatic control work? It works by using
feedback control. Information about the output variable we measure is used to
adjust the input variable we can control. When the output is too high, the input
level is reduced and when the output is too low the input is increased. To use an
example from human biology, if our body temperature is increasing in a hot day,
perspiration is used to cool down the body via evaporation.
To control, one needs to know the effect of possible action on the system
or process that is to be controlled. One needs to have a cause and effect kind of
list, so when the process evolves in an undesirable way we may intervene and
correct it.
In an automobile, the automatic speed control system, the cruise control
as it is known, detects the speed, calculates how much it is different from the
desired speed and increases or decreases the fuel by adjusting the gas pedal. This
is exactly how the driver behaves, and the automatic controller imitates the actions of the driver. Today, our cars run more efficiently and with cleaner emis-
sions because of control algorithms in the “engine control module.” The ABS
brakes would not exist without automatic control; the same with the Electronic
Stability Control systems. Our cars today are cleaner, safer and more efficient
because of automatic control.
These models are typically mathematical models that capture the behavior
of interest. The study of the models leads to identifying the variables that need
to be manipulated and by how much, in order to achieve given desired specifications. In aircraft flight, when the automatic pilot is engaged, particular control
surfaces are used to ascend, descend or turn. Detailed mathematical models are
used to decide what action should be taken, and the decision mechanisms are
implemented via algorithms coded in software that runs on digital hardware.
These algorithms process sensor information such as speed, direction, altitude together with information regarding desire altitude, speed or direction and
issue control commands to electric motors or hydraulic actuators that move the
control surfaces just the right amount.
The control specifications may refer to a static value, as in keeping the
room temperature at 68 degrees or the aircraft speed at 8 Mach, or they may
Unit 5. Automatic Control Theory
85
refer to dynamic, time-changing values, as in having an aircraft follow a par-
ticular trajectory over time, or a radar beam following, “locking on,” an aircraft
that flies overhead. Designing controllers that make complex systems exhibit
desired behaviors can be very challenging. This is because the mathematical
models, which can be quite complicated (e.g. nonlinear or partial differential
equations, automata or Petri nets) only approximately describe the behavior of
interest, and in addition, non-measurable external disturbances (e.g. load disturbances, measurement noise) may affect the behavior in an adverse way.
These ever-present uncertainties that may be internal or external to the plant
(the system to be controlled) are the principal reasons for using feedback information in the control of systems.
There are many application domains for control, each with their own particular models and requirements. Control concepts, theories, and algorithms are
used in manufacturing, in chemical processes, refineries, nuclear and non nuclear
electric energy plants, pipelines, electric transmission and distribution, transportation (air, ground water, underwater, space), economics, political science, psychology, physics, biology. More recently the area of Cyber-Physical Systems attempts to encapsulate the tight integration of computers and the physical world
in control. The common denominator of control in all these very diverse areas is
the concept of Feedback [11].
VOCABULARY IN USE
10. Complete the text with the correct words.
loops, the behavior, to achieve, system, to maintain, control, desired
A control ___(1) is defined as a system of devices that manages, commands, directs, or regulates _____(2) of other devices or systems _____(3) a desired result. A _____(4) system achieves this through control _____(5), which
are a process designed _____(6) a process variable at a _____(7) set point.
11. Read the definitions, guess the words, then use the words in the
sentences.
-l-n-
Parts in a system that can be arranged or controlled.
-o---o--e-
A device which may be situated on the external of the system or is an
element of the system itself. It functions as a control of a specific process or plant.
System analyses and control
86
--p--
A signal or stimulus put into a circuit in order to produce an outcome.
--t--t
Actual response obtained from control systems based on the input signals delivered.
---t--b---e
Undesirable signals that can hinder the output conditions of a system.
These signals may originate from outside of the system or from within
the system itself.
--e----k
A mechanism responsible for measuring output that is obtained from a
system for the purpose of delivering information to the controller so
that the compensation process can be implemented.
1. An open-loop control system is a kind of system whereby the _____ has
no effect on the actual conditions encountered. This means the _____ is not measured against the _____ or, in other words, no _____ is involved in this particular
system.
2. The open-loop control system is usually unsatisfactory because the sys-
tem cannot compensate for any _____ that occurs.
3. There are _____ that can totally eliminate the errors while there are oth-
ers that can only reduce it significantly.
4. If the controlled objective (often called _____) is exposed to fluctua-
tions or _____, the control system automatically detects such variations, and adjusts the system by feeding back a suitable control action to the _____.
5. If the system is not stable, i.e., unstable, one has to stabilize it by suita-
bly designing a _____.
COMPREHENSION CHECK
12. Decide whether the following statements are true or false (T/F) by
referring to the information in the text. Then make the necessary changes
so that the false statements become true.
1. Automatic control maintains the value of a variable constant under dif-
ferent operating conditions, manually.
2. In the human body automatic control systems are plentiful.
3. Feedback control means that information about the input variable we
measure is used to adjust the output variable we can control.
4. To control, one needs to know the impact of possible action on the sys-
tem or process that is to be regulated.
Unit 5. Automatic Control Theory
87
5. In engineering systems, automatic control mechanisms are designed
based on models of the feedback that needs to be controlled.
6. The control specifications may refer to a static value, or they may refer
to dynamic values.
7. The mathematical models precisely describe the behavior of interest.
8. Non-measurable external disturbances do not affect the behavior of the
system.
9. The concept of feedback is central to most control systems.
SPECIALIST READING
TEXT B
13. Read the text, make up a plan of the main content and write out
key words for every point of your plan.
points
key words
A control system is a system of integrated elements whose function is to
maintain a process variable at a desired value or within a desired range of values.
The control system monitors a process variable or variables, then causes some
action to occur to maintain the desired system parameter. In the example of the
central heating unit, the system monitors the temperature of the house using a
thermostat. When the temperature of the house drops to a preset value, the furnace turns on, providing a heat source. The temperature of the house increases
until a switch in the thermostat causes the furnace to turn off.
Two terms which help define a control system are input and output. Control system input is the stimulus applied to a control system from an external
source to produce a specified response from the control system. In the case of the
central heating unit, the control system input is the temperature of the house as
monitored by the thermostat.
Control system output is the actual response obtained from a control system. In the example above, the temperature dropping to a preset value on the
thermostat causes the furnace to turn on, providing heat to raise the temperature
of the house.
In the case of nuclear facilities, the input and output are defined by the
purpose of the control system. A knowledge of the input and output of the control
System analyses and control
88
system enables the components of the system to be identified. A control system
may have more than one input or output.
Control systems are classified by the control action, which is the quantity
responsible for activating the control system to produce the output. The two general classifications are open-loop and closed-loop control systems.
An open-loop control system is one in which the control action is independent of the output. An example of an open-loop control system is a chemical
addition pump with a variable speed control. The feed rate of chemicals that
maintain proper chemistry of a system is determined by an operator, who is not
part of the control system. If the chemistry of the system changes, the pump cannot respond by adjusting its feed rate (speed) without operator action.
A closed-loop control system is one in which control action is dependent
on the output. The control system maintains water level in a storage tank. The
system performs this task by continuously sensing the level in the tank and adjusting a supply valve to add more or less water to the tank. The desired level is
preset by an operator, who is not part of the system.
Feedback is information in a closed-loop control system about the condition of a process variable. This variable is compared with a desired condition to
produce the proper control action on the process. Information is continually "fed
back" to the control circuit in response to control action. In the previous example,
the actual storage tank water level, sensed by the level transmitter, is feedback to
the level controller. This feedback is compared with a desired level to produce
the required control action that will position the level control as needed to maintain the desired level.
An automatic control system is a preset closed-loop control system that
requires no operator action. This assumes the process remains in the normal
range for the control system. An automatic control system has two process variables associated with it: a controlled variable and a manipulated variable.
A controlled variable is the process variable that is maintained at a specified value or within a specified range. In the previous example, the storage tank
level is the controlled variable.
A manipulated variable is the process variable that is acted on by the control system to maintain the controlled variable at the specified value or within the
specified range. In the previous example, the flow rate of the water supplied to
the tank is the manipulated variable.
Unit 5. Automatic Control Theory
89
Functions of Automatic Control
In any automatic control system, the four basic functions that occur are:
measurement, comparison, computation, correction.
In the water tank level control system in the example above, the level
transmitter measures the level within the tank. The level transmitter sends a signal representing the tank level to the level control device, where it is compared
to a desired tank level. The level control device then computes how far to open
the supply valve to correct any difference between actual and desired tank levels.
The three functional elements needed to perform the functions of an automatic control system are: a measurement element, an error detection element,
a final control element.
The measuring element performs the measuring function by sensing and
evaluating the controlled variable. The error detection element first compares the
value of the controlled variable to the desired value, and then signals an error if
a deviation exists between the actual and desired values. The final control element responds to the error signal by correcting the manipulated variable of the
process [12,13].
14. Complete the summary of the text.
A c------ system is a system of integrated e------- whose function is to
maintain a process v------- at a desired value or within a desired range of values.
Control system i---- is the s------s applied to a control system from an
external source to produce a specified r------- from the control system.
Control system o----- is the actual r------- obtained from a control s-----.
An o--- -loop control system is one in which the c------ action is independent of the o-----.
A c----- -loop control system is one in which control a----- is dependent
on the o-----.
F------- is information in a c----- -loop control system about the c-------of a process v-------.
A controlled variable is the p------ variable that is maintained at a specified v---- or within a specified r----.
A m---------- variable is the process variable that is acted on by the control s----- to maintain the c--------- variable at the specified value or within the
s-------- range.
System analyses and control
90
SPEAKING
15. Look at the examples of control systems in daily life. Are they
examples of open-loop or closed-loop control systems? Why? Give more
examples.
1. Water Level Controller – Input water is controlled by the water level of
the reservoir.
2. Electric Hand Drier – Hot air (output) comes out as long as you keep
your hand under the machine, irrespective of how much your hand is dried.
3. Light Switch – Lamps glow whenever the light switch is on irrespective
of light is required or not.
4. An Air Conditioner – An air conditioner functions depending upon the
temperature of the room.
5. Automatic Electric Iron – Heating elements are controlled by the output
temperature of the iron.
6. Bread Toaster – This machine runs as per adjusted time irrespective of
toasting is completed or not.
WRITING
16. Write an essay in about 250 words about the future of control
systems. These links and the supplementary reading section may help you.
https://createdigital.org.au/why-automation-and-control-is-the-future/
https://www.controlglobal.com/articles/2019/the-future-of-automation-
systems/
https://www.lacconveyors.co.uk/future-of-automation/
https://www.automation.com/en-us/articles/2003-2/the-future-of-indus-
trial-automation
SUPPLEMENTARY READING
CHALLENGES IN CONTROL
The ever increasing technological demands of society impose needs for
new, more accurate, less expensive and more efficient control solutions to existing and novel problems.
Typical examples are the control demands for passenger aircraft and automobiles. At the same time, the systems to be controlled often are more
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