Transcript SYSTEMS AND CONTROL - University of KwaZulu

SYSTEMS AND CONTROL
EDTE 120 (Groups – R1 and R2)
Week 1 - 18 August 2014
ASSESSMENT OF THE COURSE
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Final module mark: 50% of your overall marks will be worked out from continuous assessment and
50% will consist of an exam mark.
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A subminimum of 40% is required in the examination component of the final module mark!
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DP requirement: 40% in the course component and 80% attendance
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Continuous Assessment:
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Classroom participation
(10 marks)
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Practical component
7 x Practicals:
7 x Tutorial:
(40 marks)
20 marks
20 marks
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1 Project
Written component
Oral presentation
(50 marks)
30 marks
20 marks
• 2 x Tests
Semester mark
(50 marks)
150 marks
UNITS TO BE COVERED
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Introduction to systems and control
Mechanical systems
Pneumatic and Hydraulic systems
Electrical systems
Objectives
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Define a system
Define control
Define control system
Identify subsystems in systems
List the 3 types of systems
Differentiate amongst the 3 types of systems.
Define what a block diagram is and how it is used to
describe a system
• Describe systems operation using flow charts
• Simulate the operation of a suggested system by
building a technological device
Accessing slides
(Slides can be accessed from:
http://talc.ukzn.ac.za/Homepage.aspx
Left Navigation….Resource Centre)
What is a system?
What is a system?
• A system is a collection of living and/or nonliving things and processes that interact to
perform some function.
• A system includes inputs, out-puts, and
relationships among system components.
• Natural and human systems develop in
response to, and are limited by, a variety of
environmental factors.
Definition of a system
A system is a combination of parts or
components, which work together to
control a task or activity.
All systems must have :
• Input(s)
• Process(es)
• Output
A systems diagram for a simple
circuit
The cell supplies
electrical energy
to the wires and
bulb.
The electric
energy flows
through the wires
and bulb.
INPUT
PROCESS
The energy
changes to light
and heat energy
within the bulb.
OUTPUT
The respiratory system
• Input?
• Processes?
• Output?
Systems approach
• There are many advantages to using a systems
approach to designing and making products.
The systems approach asks the questions:
– What does it do? (output)
– How does it do it? (process) and
– What makes it do it? (input)
Why these questions are important?
• It’s a good way of looking at an existing technical product
and understanding how it functions.
• It is also a good way of approaching the design of any
new product.
• How?
– You start with what the product must do (output),
then work out how it's going to do it (process) and
finally ask yourself what energy or other inputs it
might need for the process to take place.
Task 1
Use a systems approach to discuss how the
following systems work. Ask:
1. What does it do? (output)
2. How does it do it? (process) and
3. What makes it do it? (input)
Types of systems
• Automatic systems
– Once it has been started, it’s a system that is designed
to operate without any intervention or involvement
from a human user, e.g. traffic light system
• Semi-automatic systems
– The system needs to be triggered by a human user in
order to operate, e.g. lift, automatic shop doors.
• Manual systems
– The system allows the user to make decisions for
themselves, with the system being designed to carry
out instructions of the user, e.g. TV, VCR and stereo
systems
Systems and control
• Systems need to be controlled, to make sure
that they start working in the first place and
continue working correctly.
– Open-loop system
– Closed loop systems
Open-loop system
• In this type of system, the input triggers the
process and the process controls the output.
• It is open-ended
• It can be considered linear.
Open-loop system
Closed-loop system
• Like an open-loop they have inputs, processes and
outputs, but they also have another element called
feedback.
• Feedback is information from the output of a system
which is 'fed back' into the input to control the way the
system works.
• In this type of system the output can be checked, and the
results fed back into the system - to control it by making
changes to the input and/or process.
• They are circular and close-ended
Closed-loop system
Why a closed-loop system?
• Closed-loop systems need to be
controlled, and this is done by means of a
feedback loop which checks the outputs
and feeds the results back into the
system.
• Feedback permits us to compare actual
performance to desired performance. It
allows us control over a systems output.
Task 2
Discuss in your groups how a system controlling
an automatic barrier at a car park works.
How does it
work?
A system controlling an automatic
barrier at a car park
• It needs control feedback from the sensors
which detect the approach of a car.
• If the feedback is positive, the system changes
to 'barrier up' - if negative, the system defaults
to 'barrier down'.
In this module we will focus on:
• Mechanical Systems
• Electrical and Electronic Systems
• Pneumatic and Hydraulic Systems
References:
• Garret. J., “Design and Technology”
• biologycorner.com
• http://www.solarfreezeprotection.com/syste
ms.html
• portableappliances.com.au
• zbicyclist.blogspot.com
• http://www.umass.edu/usa/newsgrams/2007
/octoberunionvoice07/index.html
• photographersdirect.com