Chapter 2
The Engineered Systems
Abstract Engineered systems are those entities that are designed and constructed
by human beings. They include a vast array of mechanical, electromechanical,
electronic, and hydraulic devices, such as steam engines, automobiles, stereoamplifiers, computers, and wind turbines. They also include much larger entities,
for example, ships, airplanes, chemical manufacturing plants, and oil refineries,
and even larger ones, such as telecommunication networks and power grids. An
engineered system may include human beings, when they are closely associated
with its working, for example, an automobile with its driver, an airplane with its
pilots, or a chemical plant with its operating personnel. The early applications of
systems science have mostly been in the domain of Engineered Systems, where
James Watt was a forerunner. He developed feedback mechanism for controlling the
speed of steam engines. This chapter provides an overview of engineered systems
as an introduction to a broader systems thinking. The next chapter will discuss how
the same concepts can be applied to nonengineered systems.
The chapter starts with a brief history of engineered systems that came into being
at the beginning of the industrial revolution. Early mechanical systems included
water wheels and windmills, which were followed by the development of stationary
steam engines for pumping out water from the coal mines in England. Then there
are discussions on loop diagrams that depict the information flows in the systems.
The chapter delves into the various parts of a loop, which include sensors, actuators,
and controllers. Finally, there are discussions on the importance of feedback and
how delays can negatively affect the behavior of a system.
2.1 History of Engineered Systems
The Industrial Revolution, which started in Great Britain, during the eighteenth
century, totally changed the ways for producing goods for human use. This also
changed societies from being mainly agricultural to one in which industry and
manufacturing became paramount. After its adoption in England, other countries
such as Germany, the United States of America, and France joined in this revolution.
© Springer International Publishing Switzerland 2015
A. Ghosh, Dynamic Systems for Everyone, DOI 10.1007/978-3-319-10735-6_2
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2 The Engineered Systems
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In Asia, industrialization has been led by Japan and Korea, which is now being
followed by other major countries, such as China and India.
Industrial revolution led to the design of engineered systems in a large scale.
These ranged from manually controlled to partially automated and fully automated
systems. Before the industrial revolution, human societies were largely agricultural
with artisan-based small-scale industries, also known as cottage industries. In the
cottage industry era, which spanned for a very large part of mankind’s history,
there was hardly any need for mechanical feedback systems as human beings were
controlling the tools and implements for the production processes. That changed
with industrial revolution, when more and more human activities were replaced
by machines. The machines not only replaced the muscle power of humans and
animals, such as horse and bullock but also started to reduce the need for human
intervention for their operations. This drive toward automation and the need to
operate them with greater efficiency led to the systematic study of their behaviors.
The early mechanical systems were water wheels and windmills, but the big
jump in mechanization occurred when steam engines came into use. Coal, which
was abundant in England, was the fuel of choice for generating steam at that time.
Steam engines were first used for pumping water from the coal mines in England. As
mines were dug deeper and deeper water logging of those mines became a serious
problem. Each of these engines replaced hundreds of horses that were formerly used
to raise the water, bucket by bucket. These engines were large and stationary and
were difficult to operate at a constant speed. When a boiler for generating steam
became too hot it produced too much steam making the engine run too fast and
the control of the coal fire was not easy. Cold water had to be injected to a boiler
to ­reduce steam production, which was wasteful. This led James Watt to design
a system with a fly ball governor for regulating the flow of steam to an engine
and thus control its speed automatically. This device is commonly known as the
Watt Governor, which holds a central role in the paradigm shift that occurred in the
manufacturing processes during the industrial revolution.
James Watt
The person, who is remembered most in improving the efficiency and controllability of steam engines at the start of the industrial revolution, was James Watt
a Scottish engineer and an instrument maker. He was instrumental in ushering
the age of mechanical power. His inventions, which successfully combined
science and technology, contributed significantly to the industrial revolution.
James Watt was born in 1736, in Greenock, Scotland. He started working from
the age of 19 as an instrument maker and soon became interested in improving
the steam engines, which were used for pumping water from the coal mines.
He made a number of improvements to the stationary steam engines that were
increasingly used in those days. Watt designed a separate condensing chamber
for the steam engine that prevented enormous losses of steam in the cylinder
and enhanced the vacuum conditions. Watt’s first patent, in 1769, covered this
device and other improvements on the engine, which included steam-jacketing, oil lubrication, and insulation of the cylinder in order to maintain the high
2.2 The Watt Governor
21
temperatures necessary for maximum efficiency. From a systems perspective,
Watt’s most important invention was the fly-ball governor for controlling the
speed of steam engines, which is generally known as the Watt Governor.
Watt made several inventions in various other fields, such as in civil engineering
and telescopy. Watt died in Heathfield, England, in 1819. He changed the course
of the industrial revolution and was the most honored engineer of his time.
2.2 The Watt Governor
The Watt Governor consists of two iron balls located at the end of two pins that
are connected to a spindle, which is attached to the fly-wheel of a steam engine
(Fig. 2.1). There are two rings/sleeves that connect to the spindle, where the upper
sleeve is rigidly connected and the lower sleeve slides up or down. As the velocity
of the wheel increases, the centrifugal force causes the two balls to separate further;
this makes the lower sleeve move up causing reduction of the steam flow to the
engine and lower its rotational speed. Conversely, when the engine slows, the two
balls get nearer to each other resulting in increased steam flow and its rotational
speed. Thus, the rotational speed of the steam engine was kept reasonably steady
at the desired speed (or set point). The vertical position of the upper ring/sleeve is
adjusted to vary the set point of the rotational velocity.
The Watt Governor provided factories and mills a reliable and cost effective way
to regulate the rotational speed of various types of machines from water wheels
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2 The Engineered Systems
to steam engines in all types of industries. Additionally, the principles of the Watt
Governor have been applied to control of internal combustion engines and turbines.
The Watt Governor is notable as it is one of the first engineered systems using
feedback principles. This is the first time that the use of mechanical technology
was extended from power to regulation. It improved the reliability of steam engines
significantly by automating an operator’s function. Without the Watt Governor the
industrial revolution could not have progressed. Steam engines lacking automatic control would have remained very inefficient, requiring much more labor and
energy to operate them. Watt’s invention ushered in the era of engineered systems,
which took a central role in the industrial revolution.
The Watt Governor is of particular interest today because it embodied the principle of feedback, linking output to input, which is the basic concept of automation
of almost all systems. Its principles have been extensively analyzed, more than a
century later by James Clerk Maxwell the famous Scottish physicist and mathematician. His work was subsequently followed by other mathematicians, scientists,
engineers, sociologists, and psychologists.
2.3 Depiction of Information Flow (Control Loop Diagram)
In studying the behaviors of systems, we focus on the actions and interactions of
the components or subsystems. These actions and interactions are largely the result
of information or signals that flow within and between them. Textual descriptions,
while often sufficient to describe linear events, fall short of depicting these information flows adequately. This has led to the graphical representations of the systems,
which are often supplemented with texts.
Set point, controller output, feedback, and other similar things are signals or
values. Conceptually, they do not transmit any material, power, or energy. This is
true for most electromechanical and industrial systems, such as the central heating
system or the Watt Governor and is also true for many social and political systems.
These signals could be in analog or digital format and are independent of the transmission media, which could be electrical, electronic, optical, auditory, and many
others. However, in many natural and biological systems, such as in the case of
predator prey relationship, these signals are indistinguishable from material or
energy flow. In studying systems, we are primarily concerned with information flow
between the components or subsystems that affect the flow of material and energy,
or behavior rather than with the mechanisms that affect them.
Engineered systems are commonly represented graphically by control block
diagrams as shown for the home heating system in Chap. 1 and for the Watt
Governor earlier in this chapter. In a block diagram, rectangular and circular blocks
are used to represent functions or subsystems, which are connected by arrows,
which depict the signal or information flows and their directions (Figs. 2.2 and
2.3). An arrow is usually annotated to describe the type of information that it is
transmitting. Sometimes, a positive or negative sign is associated with an arrow
when two or more of such are compared. Material or energy flows are sometimes
shown in block diagrams, which are distinguished from information flow by thicker
2.4 Going Round a Loop
23
Load Change &
Other Disturbances
System
Controller
Objective/Set Point
Comparator
+
e
-
Action
Generator
Controller
Output
Process Input
(material, energy, etc.) Actuator
Sensor
Process Output
(material, energy, state, etc.)
Process
Feedback/Controlled Variable
Fig. 2.2 Block diagram of a system
sets of arrows. Physical objects, such as valves, pumps, or process vessels are often
illustrated in a block diagram to make them easier to understand. Block diagrams
are a preferred way of depicting control systems, thus it is widely used in control
engineering textbooks.
2.4 Going Round a Loop
In the following sections, we will be discussing the different parts of a typical
control loop of an engineered system, with examples of other types of systems as
appropriate. The understanding of which will give more insight about the workings
of all types of systems.
A simple engineered system consists of a process and a controller (Figs. 2.2 and
2.3). A process may be any subsystem that does something that is useful or interesting and is controlled by a controller. The home heating furnace, steam engine,
automobile, and chemical reactor are the examples of processes. A simple controller controls one of the variables of the process to produce the desired result, which
could be the room temperature for a home heating system, the desired speed in
case of a steam engine, or desired product composition and quality in the case of
a chemical reactor. The controller may be an electrical or mechanical device for a
Load Change &
Other Disturbances
System
Objective/Set Point
FC
Controller
Output
Process Output
(material, energy, state, etc.
Actuator
Process Input
(material, energy, etc.
Sensor
Process
Feedback/Controlled Variable
FC - Flow Controller
(could be other types of controllers,
like temperature, pressure, motion, etc.)
Fig. 2.3 Block diagram of a system (alternate format)
2 The Engineered Systems
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Fig. 2.4 Peer-to-peer interactions
home heating furnace or a steam engine, but it also can be a human driver in the case
of an automobile, or a teacher in the case of a student.
The block diagram of a simple control loop is suitable for depicting situations
where one subsystem is controlling another, such as between an automobile and
its driver, a teacher teaching a pupil, or a mother tending her baby. Sometimes the
controller and the process are interchangeable entities (subsystems), depending on
their roles and the way we perceive them. For example, in an interaction between
a mother and her baby the mother is generally in control, while the baby is the
process. However, the baby may be considered as a controller whom the mother
feeds whenever the baby screams.
There is however, another type of relationship, which is peer-to-peer, such as the
interaction between two friends, between married couples, or between a parent and
a grownup child. There, one is not controlling the other or each is trying to control
the other, then the loop diagram gets a bit more complicated (Fig. 2.4). Here, there
are two set points or objectives, which may or may not coincide leading to a more
complex situation.
2.4.1 Objective or Set Point
Every engineered system has one or more objectives (set points), for example, a
home heating system’s function is to maintain the temperature in one or more rooms
in a house at a set value (set point). The objective of a Watt Governor is to run a steam
engine at a set speed. In a manufacturing plant, the objective may be to maintain the
quality of its products but for an enterprise that may be to optimize profit.
In a primary school, a teacher’s objective is to impart simple verbal and
mathematical skills to her students, whereas a high school teacher may have multiple
objectives, such as imparting in-depth knowledge in chosen subjects, imparting the
2.4 Going Round a Loop
25
quest for learning, making the student a good corporate citizen, and maximizing her
chances of gaining admission in a prestigious university. A politician when elected
to a high office may have many different objectives. Many of them may be promises
made during the election campaign but her primary objective may be to increase the
chances of getting reelected. Thus, in a typical system there may be multiple objectives, but to simplify the matter we will initially be considering only one objective
at a time and leave the consideration of multiple objectives until later.
2.4.2 Controller
A controller consists of a comparator and an action generator. Some people depict
them separately, however, in real life they are mostly together, such as the controller
of a home heating system, the Watt Governor for a steam engine, a driver driving a
motor vehicle, or a teacher teaching a pupil.
Comparator
The task of a comparator is relatively simple; it is to compare the objective or the
set point with the controlled variable (feedback value). The result of the comparison
is a positive or negative value, which represents the amount by which the actual
output of the system varies from the target or the desired value, which is also called
as set point. This difference between the desired and the actual values is called error
( e). This is a distinct function, which in most cases is physically a part of the controller. Thus, the driver of an automobile functions both as a comparator, comparing
the speedometer reading with the desired speed, and as a controller adjusting the
position of the gas pedal (accelerator).
Action Generator
An action generator generates the controller output, which is based on the error
signal from the comparator. In the case of a home heating system, the thermostat
(controller) generates either an on or an off signal depending on the current room
temperature in relation to the set point. Appropriately, it is called on/off control and
such a controller as on/off controller. On/off control works well in maintaining the
temperature in a room as we human beings can generally tolerate a small variation
in the ambient temperature without much discomfort (Fig. 2.5). On/off control will
however be undesirable in many other applications, such as for driving a vehicle,
where smooth ride is an essential element for comfort. It will also be unacceptable for controlling temperature in an industrial application, where the quality of a
product is closely dependent on the temperature during the chemical reaction.
In industrial applications, proportional control action is most common, where
controller output is proportional to the error. That is, further the process output from
the target set point harder is the push to get there. For example, we increase pressure
2 The Engineered Systems
26
Controller
Output
ON
OFF
Upper
Deadband
Room
Temperature
Set point
Lower
Deadband
Time
Controller Output and Room temperature
Fig. 2.5 Behavioral response of a central heating system
on the gas pedal when a car is going slower than the desired speed. The amount of
increase in pressure we put on the gas pedal is proportional to how much we want
to speed up from the present speed. Similarly, the pressure we put on the brake
pedal is proportional to how fast we want the car to slow down. Proportional action
is used extensively in industrial applications as well as in our societal settings. Our
criminal justice systems are largely based on proportional control. When we say,
“the punishment should fit the crime” we are talking about proportionality.
The main drawback of pure proportional control action is that it produces output
only when there is error that leads to a situation where the output never reaches the
set point. Once the process output gets closer to the set point the error gets smaller
and the output of the controller gets smaller too, which may not be enough to get
all the way to the set point or the target value. This difference between set point and
controlled variable is called offset (Fig. 2.6). The offset can be reduced by increasing the proportional gain but that can lead to oscillation, which will be discussed in
a later chapter.
Offset is generally corrected by adding another function called integral control
action, whose output is based on the sum of the past errors. Integral control closes
the gap by adding up (integrating) the error and the length of time the error has
been there, thus eliminating the offset altogether. While driving a car we do that
unconsciously by increasing the pressure on gas pedal when it runs at a slower
than the expected speed and then easing off when the expected speed is reached.
Integral action is usually active in criminal justice systems where repeater offenders
are given stiffer sentences than the first time offenders. In industrial applications,
integral control is commonly used along with proportional control because integral
control is typically slower to respond on its own.
2.4 Going Round a Loop
27
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Set Point
8
Offset
6
4
Process Output
2
0
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Fig. 2.6 Proportional control with offset
There is still another common type of control action called derivative control,
where the output is based on the rate of change of an error. In other words, the
magnitude of its output is greater when there is a faster change of the error signal.
Thus, if the error increases suddenly, derivative action will act immediately, while
it may take some time for proportional and integral actions to take effect. We press
the brake pedal when we see a sudden slowing of the car in front. The faster the car
in front slows more pressure we apply to the brake pedal.
Proportional control is most common in industrial applications and integral
control is used in conjunction with proportional control to eliminate the offset, where
needed. Derivative control is used in conjunction with the other control actions
where there is the need for rapid actions for sudden disturbances. A controller
with all the three control actions is called a proportional-integral-derivative (PID)
controller (Fig. 2.7). (For more details on PID control, see Appendix 1.)
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2 The Engineered Systems
2.4.3 Actuator
An actuator acts to convert a signal (message) to something tangible such as the gas
pedal (accelerator) alters the flow of gasoline to a car (automobile) engine based on
the pressure put on it. A water tap is an actuator that alters the flow of water depending on its rotational position. An on/off electric switch is an actuator that depending
on its position allows or stops electric energy to flow to a lamp, an appliance, or a
motor.
Many different actuators are used in the industry, which include valves for controlling flow or pressure of fluids, switches for stopping or allowing the flow of
energy, and servomotors for accurate positioning of objects. Human beings use
arms and legs as actuators and so do many animals.
2.4.4 Process
As stated before, a process is a subsystem that does something useful or interesting. A home heating furnace, a student in a learning mode, an automobile travelling
from one place to another, and a steel rolling mill are examples of processes. Their
dynamics vary with their inherent nature and their setup. What we mean by dynamics is the way the output of the process changes with change in the set point, input,
or its load. For the home heating furnace, the set point is the desired temperature,
the input is the inside air, and the load is the total heat required to keep the room at
the right temperature. The load may change when the outside temperature changes
or if someone opens or closes a door or a window causing sudden change in the
room temperature.
The dynamic response due to any of these changes may be instantaneous but
more commonly there would be a lag, which may be in seconds or minutes for a
home heating system or a manufacturing plant, whereas it could be months or years
for an economic or social system.
2.4.5 Process Output and Sensor
In the case of a home heating system, the process output is the hot air, whereas for a
steel rolling mill it is the rolled steel plates. For a chemical plant, it is the chemical
produced and for water filtrations plant it is the filtered water.
Sensors are essentially converters. A sensor reads the process output and converts
it to a signal that is easy to read, understand, or interpret. The speedometer in a car
is a good example; it converts the circular motion of a wheel to the speed of the
vehicle in a way that makes it easy for the driver to understand. Dogs’ powerful
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