3. Introduction
Introduction
Control system: It is a combination of several components all work-
ing together to perform a certain function. This function is control
of physical variables such as temperature, flow rate, position, speed,
and illumination.
The ultimate goal of engineering, in particular, that of control en-
gineering is to design and build real physical systems to perform a
given task.
The task is just maintaining the main Controlled variables close to
its desired value, in spite of disturbances, by means of automatic
control.
A control system must have input, output, ways to achieve input
and output objective and control action.
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4. Introduction
Examples-1: Temperature control system
From the figure given below the temperature in the electric furnace
is measured by a thermocouple which is an analog device. ADC
converts analog temperature to a digital temperature.
This digital temperature is compared with the programmed input
temperature, and if there is any error the controller sends out a
signal to the heater through a relay.
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6. Introduction
Consider the robot arm resting at 0o [see Fig.2b]. This time a po-
tentiometer has been connected directly to the motor shaft. As the
shaft turns, the pot resistance changes. The resistance is converted
to voltage and then fedback to the controller.
To command the arm to 30o, a set-point voltage corresponding to
30o is sent to the controller. Because the actual arm is still resting
at 0o, the error signal jumps up to 30o. Immediately, the controller
starts to drive the motor in a direction to reduce the error.
As the arm approaches 30o, the controller slows the motor; when
the arm finally reaches 30o, the motor stops. If at some later time,
an external force moves the arm off the 30o mark, the error signal
would reappear, and the motor would again drive the arm to the 30o
position.
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7. Introduction
Example-3: Autonomous vehicle control
Longitudinal vehicle control has been focused on torque manage-
ment for independent wheels drive. For security and comfort pur-
pose, the vehicle speed must be tightly regulated. Longitudinal
control, involves controlling the vehicle speed to maintain a proper
spacing between vehicles.
Considering the case of an autonomous vehicle driving along some
reference trajectory, the main goal of the lateral control module is
to ensure proper tracking (by applying proper steering angle) of the
reference trajectory by correctly keeping the vehicle on the prede-
fined path with the appropriate orientation (parallel to the desired
trajectory).
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9. Components of a Control loop
Components of a Control loop
Every control system has at least a controller, an actuator (final
control element) and a plant to be controlled
Sensor: Primary element with a property of sensitivity to the phys-
ical variables.
Example: Temperature sensors (thermocouple, thermistor), level
sensor, position sensor (potentiometer), speed sensor (tacho gen-
erator)
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10. Components of a Control loop
Controlled Variables (CVs): The process variable that are going
to be controlled.
Desired value: Set point (SP) value of a controlled variable.
Manipulated Variables (MVs): The process variable that can be
adjusted in order to keep the controlled variables at or near their set
points.
Plant: the portion of a system which is to be controlled.
Example: Furnace, Robot, Vehicle
Input: applied signal or excitation signal that is applied to a control
system to get a specified output
Output: the actual response that is obtained from a control system
due to the application of the input
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11. Components of a Control loop
Disturbance: is a signal that tends to affect the value of the output
of a system. If a disturbance is created inside the system, it is called
internal. While an external disturbance is generated outside the
system.
Actuators: an electromechanical devices that takes the signal from
the controller and convert it into some kind of physical action.
Example: motor, electrically controlled valve and heating element
Controllers: devices that monitor signals from sensors and take the
necessary action to keep the process within specified limits according
to a predefined program by activating and controlling the necessary
actuators.
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12. Types of control systems
Types of control systems
Linear and Non-linear control systems
If a system obeys superposition principle, then the system is
said to be a linear system. Any system which does not obey
superposition principle is said to be a non-linear system.
Time invariant and time varying system
A time-invariant system is one whose output does not depend
explicitly on time. If the input signal x(t) produces an output
y(t), then any time shifted input, x(t + γ), results in a time
shifted output y(t + γ).
Open loop and Closed loop systems
The system in which the o/p quantity has no effect upon the
i/p quantity is called open-loop control systems. They are
easy and cheaper to build. They are not accurate.
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13. Types of control systems
Examples: washing machine and traffic light
The systems in which the o/p has a direct effect upon the i/p quan-
tity are called closed-loop control systems. They are more accurate.
They are expensive and complex to build.
Example: Temperature control, robot arm control
Analog and digital control system
In analog control system, the controller consists of traditional
analog devices and circuits, that is, linear amplifiers.
Digital control systems, in which a digital computer is used as
one of the elements. The input and output to the digital
computer must be binary numbers and hence these systems
require the use of digital to analog and analog to digital
converters
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