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CHAPTERS 5
Basics of building automatic control systems

At the heart of many automatic control systems (automatic control system) (ACS) is
an automatic control (Automatic control) (AC), automatic alarm (Automatic alarm)
(AA), automatic protection (Automatic protection) (AP), the subsystem of automatic
control (Subsystem of automatic control) (SSAC) (fig
...
1)
...
5
...

Automatic alarm – designed to alert service personnel about the limit or emergency
values of any physical parameters, the place and nature of violations of the process
...

Automated control – control, in which the collection, processing of information
about the state of the object is done automatically, and decision-making and issuance
of control commands is carried out by a person
...

An intermediate option between the ACS and a fully automatic system that operates
without human intervention can be considered the so-called Supervisory control
system, in which the operator performs the role of only the controller (supervisor),
watching the progress of the process (the operation of the control system) and taking
control "over" only in emergency situations
...
Set of devices,
providing automatic control, and the object of regulation (OR) is called the
automatic regulation system (ARS) (fig
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2)
...
5
...

Automatic control – control of objects without the participation of maintenance
personnel
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Physical quantities whose values need to be kept constant or changed in accordance
with the technological process are called regulable or output values
...

The regulatory process includes obtaining information about the regulatory
objectives and the regulated value, analyzing it, developing a solution and
implementing regulatory actions
...
The functional
diagram of the simplest ARS is shown in fig
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3
...
5
...
It consists of a master and a sensitive
element, as well as a comparison element
...

The specifying element serves to introduce into the system the required law of change
of the regulated quantity or the algorithm of the system functioning
...

The output signal of the measuring device in most cases can not be directly used to
control the actuator ARS due to low power or a mismatch in physical nature
...
Thus,
the intermediate elements convert the output signal of the measuring device in form
and size in such a way that it ensures reliable operation of the system actuators
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The actuator is an element of the system that directly affects the regulator of the
object in order to restore the desired value of the controlled variable
...
Variables that influence the
regulated values are called effects
...
5
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The change in the

Object of
regulation

controlled variable y(t) is determined by both

Fig
...
4

y (t )

the regulating action U(t) and the disturbing
f(t)
...
The regulating
effect is created by the regulator and is formed under the action of the control
algorithm (law), i
...
required law of change of control U(t)
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Dynamic properties and the
form of static characteristics introduce distortions: the actual process will differ from
the desired one
...
It will depend on the algorithm of functioning, dynamic
properties and characteristics of the object, as well as various disturbing influences
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Disturbing effects are divided into main and interference
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All other types of disturbances are called interference
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The link,
which provides the transmission of signals between elements in the direction of the
object, is called direct, and the link between the output of the object and the

controller input is the main feedback
...
The presence of feedback makes a closed loop of
actions; therefore, such systems are called closed ARS
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With positive feedback, the signal xPF of
the host signal coincides in sign with the input signal xNF, and with a negative
feedback, their signs are opposite (Fig
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5)
...

Х2

Х2
Y

Х1

Y

Х1

Negative feedback

3

3

Х1+Х2– Х3=Y

Х1+Х2+Х3=Y

Fig
...
5
A graphic image of the ARS, which shows its functional elements and the
connections between them, is called a functional diagram
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Two system states that are
qualitatively different from each other are possible: steady-state and unsteady-state
(fig
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6)
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4
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In the unsteady (dynamic) mode, the controlled variable changes with time due to a
change in external influence
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The change in the state of a
system under the action of a step effect is called a transient process

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