UNIT 4: Managing Engineering Science
This Unit introduced students to sources of information on science generally,
including searching the Internet for resources, and offered an introduction to the
International System of Units, to materials and their properties, and to control
systems.
1. Underpinning Science
The amount of knowledge of science needed to study engineering depends on the
subject, so students will need a firm understanding of chemistry if they want to
become chemical engineers, while electrical engineers will need to know some
aspects of physics, especially in relation to electricity. Some engineering subjects
will require little scientific knowledge; although an understanding of the nature of
different materials may be more relevant (see Unit 5).
Your students will probably already have GCSEs in one or more Science subjects
but, if they feel that they need a refresher, then BBC Bitesize http://wwwmaterials.eng.cam.ac.uk/mpsite/design.html is a good website to brush up on their
general science knowledge. Other websites that provide more specific help are:
Physics.org has a number of very useful pages, including A Rough Guide to
Electronics, which can be found at: MadLab
Science Aid is another useful site with individual sections on Chemistry, Physics and
Biology. The main site can be found at ScienceAid Please note that the content is
copyright so you should not print out materials for use by your students without
permission, although they can print out these materials for their own use.
For those students who need revision in Chemistry, then Doc Brown’s website Doc
Brown will be useful, although it’s not quite so visually appealing as the previous site.
Revision notes are also available at Doc Brown These are colour-coded depending
on whether they are for Organic, Inorganic or Physical Chemistry. Please note that
these materials are also copyright – students may use the materials but printing out
for use by colleges is not permitted.
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Searching for Information using the Internet
Your students will frequently need to find information to support research for projects
and assignments that you ask them to undertake. They will probably be very used to
searching already and will most likely be using a search engine, such as Google, to
carry out the search. In order to refine searches, in order to reduce the number of
‘hits’ where the results are not relevant to what is wanted, you should ensure that
your students need to know about the following techniques:
Phrase search ("")
By putting double quotes around a set of words, you are asking the search engine to
only find the set of words as written in the exact order. This is good for finding
information on books or documents, where you know the exact title. But remember
that, if you are trying to find an author, you will miss out on hits where the author’s
name may be shown with middle names or initials if you only enter “(first name)
(surname)”.
Terms you want to exclude (-)
If you put a minus sign (-) immediately before a word this tells the search engine that
you do not want pages that contain this word to appear in your results. The minus
sign should appear immediately before the word and should be preceded with a
space. For example, in the query [ project -management ], the search will return
pages relating to projects but project management will not be shown on the early
pages. If you use the minus sign as a hyphen as in the query [project-management]
then you will get the same result as in [project management]. You can exclude as
many words as you want by using the - sign in front of all of them
Wild card (*)
Just as in when you are searching for a missing file, using Windows Explorer, where
you can use [*.doc] to find all Word documents in a particular location, you can also
use the *, or wildcard, within a query, it tells the search engine to treat it as a
‘wildcard’ for an unknown term or terms and then find the best matches. The results
are often similar to those produced when the wildcard is omitted, but sometimes it’s
worth trying it for complicated searches.
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Exact search (+)
If you want the search to find an exact match to a word, even if you have misspelt it,
you can put a ‘+’ immediately before it. The result is the same as putting double
quotes (“””) around it.
Every Word Counts (Usually)
When you carry out a search, the search engine will try to find all references that
include all the words. In this way you can narrow down the number of hits. There
are some exceptions – usually words such as ‘a’, ‘the’, ‘for’ are ignored unless they
are part of a proper name. For example ‘The Queen’ will return responses to Queen
Elizabeth, while ‘Queen’ will return responses to the group by that name.
2. International System of Units
This unit provides an introduction to the International System of Units, which was
developed in 1960, based on the older metric units of metre/kilogram/second. SI is
the abbreviation of the French term Système international d'unités. As Imperial Units
are still used to some extent in this country but, more importantly, in the USA, there is
also information on those units.
It is also worth mentioning that the SI system is not static and that units are created,
and definitions modified, through international agreement between nations, as the
technology of measurement progresses, and as the precision of measurements
improves.
The SI System
There are 7 base units that your students will need to know about:
Quantity
Length
Mass
Time
Electric Current
Thermodynamic
Temperature
Luminous Intensity
Name
metre
kilogramme
second
ampere
kelvin
Unit Symbol
m
kg
s
A
K
Symbol
l (lower case L)
m
t
I (capital i)
T
candela
cd
Amount of
Substance
mole
mol
lv (a capital i with lowercase v
subscript)
n
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In addition to these, there are other non-SI units that are accepted for use with SI
units – a common one is the litre (l). Others are Dalton (Atomic mass unit)
· Astronomical unit · Day · Decibel · Degree ofarc· Electronvolt ·Hectare ·
Hour · Minute · Minute of arc · Neper · Second of arc · Tonne.
There are also a number of derived units. These are Becquerel · Coulomb · degree
Celsius · Farad · Gray · Henry · Hertz · Joule · Katal · Lumen · Lux · Newton · Ohm ·
Pascal · Radian · Siemens ·Sievert · Steradian · Tesla · Volt ·Watt · Weber
Your students will also need to know how larger and smaller units can be expressed,
depending on the prefix that is added to the above units to show multiples and
fractions. They will also need to know what the terms mean:
Standard prefixes for the SI units of measure
Name
deca- hectokilomegaSymbol
da
h
k
M
Multiples Factor
100
101
102
103
106
Name
decicentimillimicroSymbol
d
c
m
µ
0
-1
-2
-3
Fractions Factor
10
10
10
10
10-6
gigaG
109
nanon
10-9
teraT
1012
picop
10-12
petaP
1015
femtof
10-15
Writing SI unit symbols and the values of quantities.
Students need to ensure that they write down the exact terms for the SI units, the
correct form for the quantities and their correct spacing. As an example, your
students need to know that the mass of an item is expressed as 34.78 kg. Not
34.78Kg or 34.78 KG. The correct form is normally (Value)(space)(Unit Symbol) and
it is vital that the correct case is used.
The only exceptions are for the symbols for plane angular degrees, minutes and
seconds (°, ‘and “), which are placed immediately after the number with no
intervening space. For example, 78.40 or 3’ 45”.
No symbol should be pluralised. For example kgs must not be used. Neither should
you mix the full SI name and symbols; so kiloHz and kHertz are both incorrect and
should be expanded to kilohertz or reduced to kHz.
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Teaching tip!
It is vital that the correct form is used and written properly. Also that the correct
multiple or fraction is chosen. If not, some BIG mistakes can be made! A useful
exercise would be test your students’ understanding of the units and terms,
possibly by setting multiple choice questions.
If your students would like further help with this subject, a very good summary is
available at the Open University’s Open Learn website. Learning Space is available
for free access and the section on SI Units OpenLearn provides additional
information, including Scientific Notation with some example questions. The site also
has links to related topics such as:
Scales of Measurement, including ‘Order of Magnitude’: OpenLearn
Precision: OpenLearn
Imperial Units
Tutors may well remember the days when fine measurements were in ‘thous’,
meaning a thousandth of an inch, and no doubt there will be many workshops that
still have micrometers that measure in these units. Your students should know about
these measures in case they are involved with the purchase of items from the USA or
in the quotation for sale to the USA. They should also know the conversion factors to
change between the units. Please note that the follow conversion rates are
approximate and that abbreviations of Imperial Units are less rigid than SI:
Units of Length
1 inch ( in. or " )
12 inches ( in.)
3 feet ( ft. )
1760 yards (yd)
8 furlongs
=
=
=
=
=
1 foot
1 yard
1 mile ( mi )
1 mile ( mi )
= 25.4 mm
= 305 mm
= 0.91 m
= 1.61 km
= 1610 m
Units of Area
144 square inch (sq.in)
9 square feet ( sq.ft)
4840 square yards (sq.yd)
4840 square yards
=
=
=
=
1 sq.foot
1 sq.yard
1 acre
1 acre
= 0.093 m2
= 0.84 m2
= 4047 m2
= 0.4 hectare
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Units of Mass or Weight
16 drams ( dr )
16 ounces ( oz.)
14 pounds ( lb)
8 stone
20 hundredweight (cwt)
Units of Capacity
5 fluid ounces
20 fluid ounces
2 pints( pt.)
4 quarts ( qt )
But note:
16 US fluid ounces
8 US pints
Units of Volume
1728 cubic inches
27 cubic feet
=
=
=
=
=
1 ounce
1 pound
1 stone
1 hundredweight
1 ton
= 28 g
= 0.45 kg
= 6.35 kg
= 50.8 kg
= 1.016 tonne
=
=
=
=
1 gill
1 pint
1 quart
1 gallon
= 142 ml
= 568 ml
= 1.1 l
= 4.546 l
=
=
1 US pint
1 US gallon
= 475 ml
= 3.785 l
=
=
1 cu.foot
1 cu.yard
= 0.028 m3
= 0.76 m3
Teaching tip!
Your students may not be familiar with stones, pounds and ounces, although
they may well be very familiar with pints! It would be a worthwhile exercise to
show the conversion factors needed between the Imperials Units used for
weight or length to show how much easier a metric system is to use. To show
further oddities – you may wish to mention the American Imperial Units shown
below.
American Weights
Just to add to the confusion when using Imperial Units, you might like to mention the
following:
The hundredweight (cwt) in England is always 112 pounds, or 8 stone. In the USA,
the hundredweight is 100 lb, unless noted as otherwise. It is proper to call a 100 lb
hundredweight a short hundredweight, and a 112 lb one a long hundredweight. As
there are always 20 cwt to the ton, in the US it is normal to use a 2000 lb ton
(a short ton), and in England a 2240 lb ton (a long ton).
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3. Materials and their Properties
Just as in the previous unit, your students may need to acquire different degrees of
knowledge about materials and their properties. As examples, mechanical engineers
will certainly need to know about metals, while civil engineers will need to know
about a much wider range of materials that are currently found in structures.
This unit is designed to be an introduction to materials science and the link to the
pages at University of Cambridge is of particular value as they show how various
materials need to be selected for particular end uses
Teaching tip!
To emphasise the need to consider the properties of a range of materials in
terms of their suitability for particular uses, get your students to consider the
properties of wood, paper, steel and stone for their potential use in constructing
planes, buildings, bridges and boats. What would be the limitations of using
some of these materials? Could some of these materials be made more useful if
they were modified? Think of resin-coated paper or concrete.
The Product Design section at the University of Cambridge’s website Cambridge is
particularly useful as it shows the relationship between such properties as strength,
temperature, toughness, for a number of projects. There is also a very useful tutorial
that you would be advised to read first if you want to cover material science in your
own tutorial. This can be found at: Cambridge
If your students need more information on polymers they will find it at the Open
University’s website
OpenLearn
4: Control Systems
This unit was also included at the request of students in the focus group. The content
of the unit is provided as an introduction to the subject. Control systems are now a
very common feature of daily life. At one time they were used to control and regulate
industrial machinery or whole factories, but are now commonly found in the home in
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virtually all domestic appliances – even electric kettles have a control that switches
them off when the water boils.
Teaching tip!
Ask your students to provide a number of examples where controls systems are
in use, which they might encounter in their daily lives. What function do they
perform? Do they regulate something to give a steady state; are they just
stop/start; or do they provide a programme of steps towards an end-point?
Examples might be traffic lights, access systems, lifts, washing machines, etc.
It would also be useful to provide your students with examples of mechanical,
hydraulic and pneumatic control systems, to show that many things are still not
‘computer controlled’.
Control and Control Loops
Your students will need to know about the feedback loop, as shown in this diagram:
You should explain that the sensor measures the output from the system, for
example temperature, and then feeds the measurement to the controller. If the
measurement is outside the acceptable range then the controller will make an
adjustment to the system to bring it back within the set limits. For example, if a
chemical is being added to a chemical reaction and the temperature rises, the
controller could either reduce the rate of addition and/or increase the rate of cooling
until the temperature of the reaction is within the acceptable range. In practice,
modern control systems are sufficiently clever that they can measure the rate of
temperature increase and take steps to prevent a set temperature from being
exceeded. This is an example of a closed loop control system.
Students also need to know about open loop control systems. Speed control on a car
as examples of both:
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A cruise control system in a car is an example of a closed loop system. The fuel
injection system will pump more fuel into the car engine if it senses that the car is
slowing down as it starts to ascend a hill. In old cars, some were fitted with a manual
throttle control. If the car was travelling on a flat road, it was possible to set the
throttle to maintain a speed. However, there was no feedback – if the car started to
go up a hill, it would slow down and would only regain its speed if the driver adjusted
the manual throttle again. This is an example of an open loop control system – there
is no feedback to make adjustments to maintain the speed.
PID Controllers
It would be useful to mention PID (proportional–integral–derivative) controllers, which
measure the rate of increase of a parameter, such as temperature, and then make
adjustments. A good description of how they work can be found at: Wikipedia
Feed forward control
You should mention a limitation of the PID controller, in that the settings to control
the system have to be refined and are then fixed. Some systems behave in different
ways over time or during a process, and knowledge of how the system behaves
needs to be known, in order to further refine the control. Feed forward control is an
example of using an open loop control system to further refine PID control. An
example of where this might be used is in starting up a moving object – more torque
will be required at start-up but, once moving, speed control would be by PID control.
The feed forward control would be used at start-up.
Types of Control Systems
The various types of control systems that are available need to be mentioned.
Fluidic Control. Pneumatic systems use a compressed gas, such as air, nitrogen or
carbon dioxide, to open and close valves, regulate speed, control temperature, etc.
These systems are safe to use in hazardous areas, are simple to design and cheap
to install. They were once the most common form of control before PLCs and
computers became more commonly available. A variation is the hydraulic control
system which uses a non-compressible fluid and so can exert greater forces. BBC
Bitesize has a good section on pneumatic control and the contents of the site could
be usefully used to explain pneumatic control in a tutorial at: BiteSize
Further information on simple pneumatic controls and a more-detailed description of
the various pneumatic switches and devices can be found FPEF
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The following diagram shows a simple pneumatic circuit to control two cylinders:
Fluid control systems use logic to control actions. Your students need to know about
some of the more-common switches (or gates):
AND gate: Circuit has two or more inputs, and one output that is high if all inputs are
high.
NAND gate: Circuit has two or more inputs, and one output that is high if one or more
of the inputs are low, and low if all the inputs are high.
OR gate: Circuit has two or more inputs, and one output that is high if one or more of
the inputs are high.
NOR gate: Circuit has two or more inputs, and one output that is high only if all inputs
are low.
INVERTER (NOT gate): Circuit has one input, and one output that is high if the input
is low and low if the input is high.
The following website has Flash animation that shows the logic behind some of these
gates: Mekanizmalar
The principal behind the logic gates is also used in electronic control. Programmable
logic control. PLCs are the most common form of control. They can be found in
factory automation, process control, manufacturing systems and domestic
appliances such as washing machines. They are simple computer chips that are
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programmed using a special technique called ladder logic, which allows sequences
of logical actions to be set up, interlinked and timed. A standard task in logic control
is batch control and sequencing in a process system.
Distributed control system. A DCS is a computer control system commonly found in
manufacturing where there are a number of sensors, actuators and other controllers,
distributed around the manufacturing plant. The entire system is connected by a
network to one or more control points, which monitor the system, collect data and
make adjustments as needed. A DCS provides more functionality than would be
possible with simple PLC control, having extensive computational capability and, in
addition to PID control, can generally perform logic and sequential control.
SCADA (supervisory control and data acquisition) is a variation on the DCS. It refers
to a centralised system, which monitors and controls entire sites, or complexes of
systems spread out over large areas. Most control actions are performed
automatically by Remote Terminal Units (RTUs) or by PLCs. Host control functions
are usually restricted to basic overriding or supervisory level intervention. For
example, a PLC may control the flow of cooling water through part of an industrial
process, but the SCADA system may allow operators to change the set points for the
flow, and enable alarm conditions, such as loss of flow and high temperature, to be
displayed and recorded. The feedback control loop passes through the RTU or PLC,
while the SCADA system monitors the overall performance of the loop.
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Teaching tip!
Finally, if you would like to demonstrate to your students how various
parameters can affect the control of an oven’s temperature using a simple on/off
thermostat or a PID controller, there is a useful exercise at the following website:
Exeter
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