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lecture 2
Ali Karimpour Sep 2015
Ali Karimpour
Associate Professor
Ferdowsi University of Mashhad
CONTROL IN
INSTRUMENTATION
References:
1- Modern Control Technologies: Components and Systems, 2nd Edition, by Kilian,
Delmar Publication Co, 2005
2- Power Points of Dr. Hamed Molla Ahmadian
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Ali Karimpour Sep 2015
2
Lecture 2
An Introduction to Control in
Instrumentation
Topics to be covered include:
v Introduction
v Block Diagram
v Open-loop and Closed-loop Systems
v Transfer Functions
v Analog and Digital Control Systems
v Classification of Control Systems
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An Introduction to Control in
Instrumentation
v Introduction.
v Block Diagram.
v Open-loop and Closed-loop Systems.
v Transfer Functions.
v Analog and Digital Control Systems.
v Classification of Control Systems.
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Introduction
Control System An interconnection of components forming a system
configuration that will provide a desired response.
Control is the process of causing a system variable such as temperature to
conform to some desired value.
System An interconnection of elements and devices for a desired purpose.
Controller In most cases, electronic circuits provide the intelligence, and
electromechanical components such as sensors and motors provide the
interface to the physical world.
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Introduction: Sensor and Actuator
A simple Governor
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Introduction: Sensor and Actuator
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Water-level float regulator (before BC)
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Introduction: Earlier Control Systems
7
Human System
i. Pancreas
Regulates blood glucose level
ii. Adrenaline
Automatically generated to increase the heart rate and oxygen in times of flight
iii. Eye
Follow moving object
iv. Hand
Pick up an object and place it at a predetermined location
v. Temperature
Regulated temperature of 36°C to 37°C
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Introduction: Transportation
Car and Driver
v Objective: To control direction and speed of car
v Outputs: Actual direction and speed of car
v Control inputs: Road markings and speed signs
v Disturbances: Road surface and grade, wind, obstacles
v Possible subsystems: The car alone, power steering system, breaking
system 8
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Introduction: Transportation
Functional block diagram:
Time response:Measurement, visual and tactile
Steering
MechanismAutomobileDriver
Desired
course
of travel
Actual
course
of travelError+
-
9
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Sensors are the eyes of control enabling one to see
what is going on. Indeed, one statement that is
sometimes made about control is:
If you can measure it, you can control it.
As an example consider the altitude sensor in an
aeroplane or the temperature in a room.
Introduction: Sensor and Actuator
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Once sensors are in place to report on the state of a
process, then the next issue is the ability to affect, or
actuate, the system in order to move the process
from the current state to a desired state.
As an example consider the ballet in an aeroplane or
the fan in a room.
Introduction: Sensor and Actuator
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In summary:
Sensors provide the eyes and actuators the muscle
but control science provides the finesse.
Introduction: Sensor and Actuator
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Better Control(Computing)Provides more finesse by combining sensors and
actuators in more intelligent ways
Better ActuatorsProvide more Muscle
Better Sensors
Provide better Vision
Introduction: Sensor and Actuator
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An Introduction to Control in
Instrumentation
v Introduction.
v Block Diagram.
v Open-loop and Closed-loop Systems.
v Transfer Functions.
v Analog and Digital Control Systems.
v Classification of Control Systems.
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Block Diagram
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v Block Diagram of a Control System
v Open Loop Control
v Closed Loop Control
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v An open-loop control system utilizes an actuating device to control the
process directly without using feedback.
v A closed-loop feedback control system uses a measurement of the
output and feedback of the output signal to compare it with the desired
output or reference.
Actuating
DeviceProcess Output
Desired Output
Response
Desired
Output
Response
Measurement
OutputController ProcessComparison
Open-loop and Closed-loop System
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Open-loop and Closed-loop System
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Open-loop System
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Open-loop and Closed-loop System
Closed-loop System
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An Introduction to Control in
Instrumentation
v Introduction.
v Block Diagram.
v Open-loop and Closed-loop Systems.
v Transfer Functions.
v Analog and Digital Control Systems.
v Classification of Control Systems.
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Ali Karimpour Sep 2015
Transfer Functions
20
Physically, a control system is a collection of components and
circuits connected together to perform a useful function.
Each component in the system converts energy from one form to
another; (for example, temperature sensor or a motor)
A transfer function (TF) is a mathematical relationship between
the input and output of a control system component.
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Transfer Functions
21
A System With three TF:
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An Introduction to Control in
Instrumentation
v Introduction.
v Block Diagram.
v Open-loop and Closed-loop Systems.
v Transfer Functions.
v Analog and Digital Control Systems.
v Classification of Control Systems.
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Ali Karimpour Sep 2015
Analog and Digital Control Systems
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• A program executes over-and-over (iteration or scan).
• The total time for one pass through the program may be less than 1 millisecond.
• The digital system only “looks” at the inputs at a certain time.
In an analog control system, the controller consists of traditional
analog devices and circuits, that is, linear amplifiers.
• Older times it was the only available technology.
• Change in either set point or feedback is sensed immediately
In a digital control system, the controller uses a digital circuit. In
most cases, this circuit is actually a computer, usually microprocessor-
or microcontroller-based.
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Analog and Digital Control Systems
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A digital control system
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Analog and Digital Control Systems
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Analog Control
v Advantages:
1. Speed of Operation
2. Simplicity for many cases
3. No need DAC and ADC
v Disadvantages:
1. Noise
2. Hardware Implementation and Limitations
3. Low Flexibility
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An Introduction to Control in
Instrumentation
v Introduction.
v Block Diagram.
v Open-loop and Closed-loop Systems.
v Transfer Functions.
v Analog and Digital Control Systems.
v Classification of Control Systems.
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Process control refers to a control system that oversees some
industrial process so that a uniform, correct output is maintained.
Classification of Control Systems
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Control system for a boiler of a thermal plant
Classification of Control Systems
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A typical industrial control problem will usually
involve many different actuators - see below:
Classification of Control Systems
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Classification of Control Systems
Manual Control
Automatic Flow Control
Automatic Color Control
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Classification of Control Systems
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v Approaches of Multi process Control:
u Individual local controllers
u Direct computer control
u Distributed computer control
Classification of Control Systems
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v Sequentially Controlled Systems: A sequentially controlled
system controls a process that is defined as a series of tasks to be
performed that is, a sequence of operations, one after the other.
Classification of Control Systems
• Time-driven (open-loop control)
• Event-driven (closed-loop control)
v Examples: washing Machine, Traffic Control and Packing Materials.
v Many Tasks one after one control by PLCs.
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Classification of Control Systems
• Such a system typically includes a motor, mechanical parts that move,
and (in many cases) feedback sensor(s).
• Examples: Automatic assembling machines, industrial robots and
numerical control machines.
v Motion Control: Motion control is a broad term used to describe an open-
loop or closed-loop electromechanical system wherein things are moving.
• It has some categories such as:
• Servomechanisms,
• Numerical Control,
• Robotics.
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Classification of Control Systems
Servomechanism is the traditional term applied to describe a closed-
loop electromechanical control system that directs the precise
movement of a physical object such as a radar antenna or robot arm.
A remote antenna
Positioning system.
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Classification of Control Systems
Numerical control (NC) is the type of digital control used on machine
tools such as lathes and milling machines.
These machines can automatically cut and shape the work piece
without a human operator.
Numerical control
milling machine.
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Classification of Control Systems
Industrial robots are classic examples of position control systems.
In most cases, the robot has a single arm with shoulder, elbow, and
wrist joints, as well as some kind of hand known as an end effector.
A pick-and-place robot
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Exercises
38
1- In a certain system, an electric heating element was found to increase the
temperature of a piece of metal 10° for each ampere of current. The metal expands
0.001 in./deg and pushes on a load sensor which outputs 1 V/0.005 in. of
compression.
a. Find the transfer functions of the three components and draw the block diagram.
b. Calculate the overall transfer function of this system.
2- The iteration time of a digital controller is 1 s. Would this controller be
appropriate for the following?
a. A robot that paint sprays cars
b. A solar panel control system that tracks the sun across the sky
3- Give an example (other than in this lecture) of the following:
a. A time-driven control system
b. An event-driven control system
c. A combined time- and event-driven control system
4- Give an example (other than in this lecture) of a servomechanism.
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Exercises
39
. می باشدجوشکاریهدف کنترل موقعیت بازوهای . در شکل نشان داده شده استجوشکاررباتک ی-5. و اغتشاش را در این ساختار مشخص کنیدعملگر، سنسور