Importance of control systems
RME 3204: Introduction to Control Systems
A Control system is an interconnection of components forming a
system configuration that will provide a desired system response.
Dr. Md. Zahurul Haq, Ph.D., CEA, FBSME, FIEB
Primary Reasons
Professor
Department of Mechanical Engineering
Bangladesh University of Engineering & Technology (BUET)
Dhaka-1000, Bangladesh
◮ Power amplification
◮ Remote control
◮ Convenience of input form
◮ Compensation for disturbances
http://zahurul.buet.ac.bd/
Important Outcomes
RME 3204: Control Systems Design
◮ Increased productivity and lower product cost
◮ Better and more uniform quality of product
◮ Greater safety for operating personnel
Department of Robotics and Mechatronics Engineering,
University of Dhaka
http://zahurul.buet.ac.bd/RME3204/
© Dr. Md. Zahurul Haq (BUET)
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Example: Manual Control System
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Example: Automatic Control System
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Example: Automatic Mechanical Control System
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Watt’s fly-ball mechanical governor
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An open-loop control system utilizes an actuating device to control the
process directly without using feedback.
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A closed-loop control system uses a measurement of the output and
feedback of this signal to compare it with the desired output (reference or
command).
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Digital control system.
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Multivariable control system.
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Coordinated control system for a boiler-generator.
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Elements of Closed-loop Control System
Controlled Variable is the actual variable being monitored and
maintained at a desired value in the manufacturing process.
Measured Variable is the condition of the controlled variable at a
specific point in time.
Measurement Device senses the measured variable and produces an
output signal that represents the status of the controlled variable.
Feedback Signal is the output of the measurement device.
Setpoint is the prescribed input value applied to the loop that
indicates the desired condition of the controlled variable.
Error Detector compares the setpoint to the feedback signal.
Error Signal is the output of the error detector.
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Example: Industrial Temperature Control System
Controller is the “brain” of the system. It receives the error signal
(for closed-loop control) as its input, and develops an output
signal that causes the controlled variable to become the value
specified by the setpoint.
Actuator is the “muscle” of the system. It is a device that alters
some type of energy or fuel supply, causing the controlled variable
to match the desired setpoint.
Manipulated Variable: The amount of fuel or energy that is
altered by the actuator is referred to as the manipulated variable.
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Block Diagram & Abbreviations
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Analog & Digital Controllers
z
controller
w
+
e controlling
element
yr
actuator
y
– r
final
control
element
x
system
measuring
equipment
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w
y
r
yr
: reference variable
: manipulated variable
: feedback variable
: controller output variable
© Dr. Md. Zahurul Haq (BUET)
x
z
e
: controlled variable
: disturbance variable
: error (≡ w − r )
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Control Modes
Analog Controller:
◮ Controllers are built using OP-amp.
◮ These are used where there is less requirement for very high
accuracy.
◮ These have clear advantages in extremely fast control loops.
Digital Controller:
◮ Input variables must initially be digitized before the signal can be
processed by the microprocessor. Manipulated variable is then
converted back to an analog signal using DAC.
◮ Increased accuracy of control, depending on the measurement signal
and the technology used.
◮ High flexibility in the structure and characteristics of the controller.
Controller action can be modified by modifying the program, and
controller parameters can be optimized automatically.
◮ Complex control strategy can be implemented fairly easily.
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