Cambridge
TECHNICALS
CAMBRIDGE TECHNICALS
IN ENGINEERING
LEVEL 3 UNIT 15 – ELECTRICAL, MECHANICAL,
HYDRAULIC AND PNEUMATIC CONTROL
DELIVERY GUIDE
Version 1
OCR LEVEL 3 CAMBRIDGE TECHNICALS IN ENGINEERING
CONTENTS
Introduction3
Related Activities
4
Key Terms
5
Misconceptions7
Suggested Activities:
ELECTRICAL, MECHANICAL, HYDRAULIC AND PNEUMATIC CONTROL
Learning Outcome (LO1)
8
Learning Outcome (LO2)
10
Learning Outcome (LO3)
11
Learning Outcome (LO4)
13
2
OCR has collaborated with current practitioners to ensure that the ideas put forward in
this Delivery Guide are practical, realistic and dynamic. The Guide is structured by learning
outcome so you can see how each activity helps you cover the requirements of this unit.
We appreciate that practitioners are knowledgeable in relation to what works for them
and their learners. Therefore, the resources we have produced should not restrict or
impact on practitioners’ creativity to deliver excellent learning opportunities.
Unit 8 Electrical operations
LO1
Understand the mechanical elements of a control system
LO2
Understand the electrical elements of control systems
LO3
Understand simple hydraulic systems
LO4
Understand simple pneumatic systems
Whether you are an experienced practitioner or new to the sector, we hope you find
something in this guide which will help you to deliver excellent learning opportunities.
If you have any feedback on this Delivery Guide or suggestions for other resources you
would like OCR to develop, please email resources.feedback@ocr.org.uk.
Unit aim
Opportunities for English and maths
skills development
Automated machines used by industry are operated by systems of control, which include
electrical, mechanical, hydraulic and pneumatic control – this requires engineers to have a
sound understanding of the processes and theory which underpin the operation of these
machines.
We believe that being able to make good progress in English and maths is essential to
learners in both of these contexts and on a range of learning programmes. To help you
enable your learners to progress in these subjects, we have signposted opportunities
for English and maths skills practice within this resource. These suggestions are for
guidance only. They are not designed to replace your own subject knowledge and
expertise in deciding what is most appropriate for your learners.
The aim of this unit is for learners to develop a foundation of knowledge and
understanding of how these control systems work.
EnglishMaths
Learners will gain an understanding of mechanisms used in control systems, and how
their design can deliver the desired motion and performance. They will be able to develop
their knowledge of electric motor types commonly used in automation control, and how
their construction relates to output characteristics.
They will gain an understanding of simple hydraulic control systems, including valves and
actuators, and a basic understanding of fluid transmission. They will gain an understanding
also of simple pneumatic control systems.
Please note
The timings for the suggested activities in this Delivery Guide DO NOT relate
to the Guided Learning Hours (GLHs) for each unit.
Assessment guidance can be found within the Unit document available from
www.ocr.org.uk.
The latest version of this Delivery Guide can be downloaded from the OCR website.
3
ELECTRICAL, MECHANICAL, HYDRAULIC AND PNEUMATIC CONTROL
This Delivery Guide has been developed to provide practitioners with a variety of
creative and practical ideas to support the delivery of this qualification. The Guide
is a collection of lesson ideas with associated activities, which you may find helpful
as you plan your lessons.
OCR LEVEL 3 CAMBRIDGE TECHNICALS IN ENGINEERING
INTRODUCTION
3
OCR LEVEL 3 CAMBRIDGE TECHNICALS IN ENGINEERING
RELATED ACTIVITIES
The Suggested Activities in this Delivery Guide listed below have also been related to other Cambridge Technicals in Engineering units/Learning Outcomes (LOs). This could help with
delivery planning and enable learners to cover multiple parts of units.
This unit (Unit 15) Title of suggested activity
LO1
LO2
LO3
Other units/LOs
Types of motion
Unit 2 Science for engineering
LO2 Understand fundamental scientific principles of mechanical engineering
Mechanical elements for producing motion
Unit 3 Principles of mechanical
engineering
LO1 Understand systems of forces and types of loading on mechanical
components
Friction in machines
Unit 3 Principles of mechanical
engineering
LO5 Understand principles of dynamic systems
The role of sensors and actuators in a control
system
Unit 7 Electrical devices
LO2 Understand electrical sensors and actuators
Unit 14 Automation control and
robotics
LO1 Understand control system theory in engineering
Common types of electrical actuators
Unit 15 Electrical, mechanical,
hydraulic and pneumatic control
LO1 Understand the mechanical elements of control systems
Motor control
Unit 14 Automation control and
robotics
LO1 Understand control system theory in engineering
Fluid transmission in hydraulic systems
Unit 2 Science for engineering
LO5 Know the basic principles of fluid mechanics
ELECTRICAL, MECHANICAL, HYDRAULIC AND PNEUMATIC CONTROL
4
Explanations of the key terms used within this unit, in the context of this unit
5
Key term
Explanation
AC motor
A motor that is powered by an alternating current supply.
Acceleration
The change in velocity of an object with respect to time.
Adiabatic
When no flow of energy occurs from a gas during expansion or compression there will be a temperature change. Such a change is said to be adiabatic.
Angular motion
Angular motion can be defined as the motion of a body about a fixed axis (or fixed point).
Asynchronous
motor
An induction or asynchronous motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic
induction from the magnetic field of the stator winding.
Boyle’s Law
In an ideal gas where the mass and temperature remain constant, the volume of the gas varies inversely with the pressure: pV = a constant
Charles’ Law
In an ideal gas where the mass and pressure remain constant, the volume of the gas varies directly with the absolute temperature: V/T = a constant
DC motor
A motor that is powered by a direct current supply.
Dynamic balancing
For dynamic balancing, not only must the masses around the axis of rotation be zero but also the moments along the axis of rotation equal zero.
Humidity
The amount of water vapour in the atmosphere or in a gas.
Ideal gas
A gas that follows Boyle’s Law and Charles’ Law.
Isothermal
Where the expansion of a gas takes place at constant temperature. In this case Boyle’s law is observed, where the volume of the gas varies inversely with the
pressure.
Kinetic friction
When a body has relative motion between it and the surface it is on, kinetic friction is the frictional force still acting between the two surfaces. It is generally lower
than the value for static friction.
Linear motion
Travel in a straight line. According to Newton’s first law of motion, a body with no net force acting on it will either remain at rest or continue to move with uniform
speed in a straight line, according to its initial condition of motion.
Servo motor
A servo motor is a rotary actuator that allows for precise control of angular position, velocity and acceleration. It consists of a suitable motor coupled to a sensor for
position feedback. It also requires a relatively sophisticated controller, often a dedicated module designed specifically for use with servomotors.
ELECTRICAL, MECHANICAL, HYDRAULIC AND PNEUMATIC CONTROL
UNIT 15 – ELECTRICAL, MECHANICAL, HYDRAULIC AND PNEUMATIC CONTROL
OCR LEVEL 3 CAMBRIDGE TECHNICALS IN ENGINEERING
KEY TERMS
OCR LEVEL 3 CAMBRIDGE TECHNICALS IN ENGINEERING
Explanations of the key terms used within this unit, in the context of this unit
Key term
Explanation
Static balancing
A shaft is said to be in static balance if the sum of all the off centre masses turning moments around the axis of rotation are zero. In other words when the shaft is at
rest in any angle of rotation no resulting moment exists to rotate the shaft.
Static friction
Static friction is the friction experienced when we try to move a stationary body on a surface, without actually causing any relative motion between the body and
the surface which it is on.
Stepper motor
A stepper motor is a special type of electric motor that moves in increments, or steps, rather than turning smoothly as a conventional motor does. The size of the
increment is measured in degrees and can vary depending on the application.
Synchronous motor
An alternating-current motor that runs at a speed that is equal to or is a multiple of the frequency of the supply.
Velocity
The distance travelled by an object with respect to time.
ELECTRICAL, MECHANICAL, HYDRAULIC AND PNEUMATIC CONTROL
6
7
What is the misconception?
How can this be overcome?
Resources which could help
Angular motion produces
centripedal not centrifugal forces
The motion of an object in a circle requires that there be an inward net force – the centripetal force.
This can be demonstrated with the tennis ball on a piece of paper demonstration outlined in the web
resource.
http://www.physicsclassroom.
com/class/circles/Lesson-1/TheForbidden-F-Word
SI units for rotational speed are not
revs/minute
Learners are used to rotational speed of engines quoted in rpm. SI units are radians/second. Impress
there are 2π radians in one rotation therefore can convert one to the other.
http://physics.tutorvista.com/
motion/rotational-speed.html
Friction is dependant upon contact
area
Learners often assume that friction increases with contact area as performance cars have large tyres.
Standard model for friction has no area component in F = µN. Tyres are an exception to the standard
model that is applicable to “hard” engineering surfaces.
http://hyperphysics.phy-astr.gsu.
edu/hbase/frict3.html
That hydraulic pumps produce
pressure
A pump produces liquid movement or flow. The pressure of the fluid at the pump outlet is zero for a
pump not connected to a system (load). A pump delivering into a system, the pressure will rise only to
the level necessary to overcome the resistance of the load.
http://hydraulicspneumatics.
com/200/TechZone/
HydraulicPumpsM/Article/
False/6401/TechZoneHydraulicPumpsM
ELECTRICAL, MECHANICAL, HYDRAULIC AND PNEUMATIC CONTROL
Some common misconceptions and guidance on how they could be overcome
OCR LEVEL 3 CAMBRIDGE TECHNICALS IN ENGINEERING
MISCONCEPTIONS
OCR LEVEL 3 CAMBRIDGE TECHNICALS IN ENGINEERING
SUGGESTED ACTIVITIES
LO No:
1
LO Title:
Understand the mechanical elements of a control system
Title of suggested
activity
Suggested activities
Suggested timings
Also related to
Teachers could explain that motion can be broken down as linear or angular, and could explain this
with the example of a crankshaft mechanism.
3 hours
Unit 2 LO2
Types of motion
Source: http://www.britannica.com/EBchecked/topic/548729/slider-crank-mechanism
ELECTRICAL, MECHANICAL, HYDRAULIC AND PNEUMATIC CONTROL
For linear motion teachers could then introduce the basic physics of point C, defining that linear
motion as the motion of a point in a straight line (Newton’s first law). Explain that motion from a
reference point as a distance (s) in a given time (t), Velocity = ds/dt, Acc = dv/dt. Mechanical Science
by Bolton is a useful text. Web based resources such as the following website may also prove useful
https://www.youtube.com/watch?v=MfDv4FMDlpI
For angular motion teachers could then introduce the basic physics of point B, defining that rotary
motion is the amount of angular rotation (θ) of a point about an origin (A) in a given time (t). Develop
from this that angular vel ω = dθ/dt and angular acceleration = dω/dt. Mechanical Science by Bolton
is a useful text. ISBN-13: 978-1405137942 Blackwell publishing.
http://www.amazon.co.uk/Mechanical-Science-3e-Bolton/dp/1405137940
Web based resources such as the following website may also prove useful https://www.youtube.com/
watch?v=nb4VzvfkSN0&index=35&list=PL6Pw5RXSrjGNN6Kp1fq7X_rgoGu6qKM8j
Teachers could then go on to relate this to automated production lines and define the two basic
types of continuous and intermittent operation. These two videos are good examples illustrate them.
Teachers could get learners to watch and comment upon the differences.
Intermittent motion: https://www.youtube.com/watch?v=fFOXPpe3Pj4
Continuous motion: https://www.youtube.com/watch?v=R_e4ZZvNA8M
8
Suggested activities
Suggested timings
Also related to
Mechanical elements for
producing motion
Teachers could introduce common mechanical elements for producing linear and rotary motion
with reference to the crankshaft mechanism used in the previous lesson and relate this to an internal
combustion engine, and the physical nature of the parts to achieve the motion. Teachers could
introduce the concept of forces and the relationship of Newton’s 2nd Law, F = ma. Relating this to the
internal combustion engine, learners could explore what limits the maximum rpm of an engine.
4 hours
Unit 3 LO1
See Lesson Element Mechanical
elements for producing motion
Mechanisms for producing
motion
Teachers could explain with the aid of models or computer animations, devices that convert rotary
3 hours
to linear motion. For example, rack and pinion, belt drives, conveyors, four bar linkages. Teachers
could then go on to explain with the aid of models or computer animations, devices for producing
intermittent motion. For example, Geneva spur, ratchet and pawl, walking beam. Web based resources
may prove useful for these.
Balancing of rotating masses
Teachers could develop the work on angular motion, and forces to explain that rotating machine
elements will cause vibration unless they are balanced. The concepts of static and dynamic balancing
could be explained and how to calculate out of balance forces. Mechanical Science by Bolton is a
useful text. Web based resources such as the following website may also prove useful
https://www.youtube.com/watch?v=YR4K-u01I1Q. Teachers can go on to explain the consequences
of unbalanced elements with regard to vibration, component damage, noise, accelerated wear.
Friction in machines
9
3 hours
Teachers could expand upon the work from unit 3 to explore the effects of friction on machines.
2 hours
Teachers should look at the equation F = µN. Static and kinetic friction coefficients µs and µk could be
explained with reference to tables in http://www.engineeringtoolbox.com/friction-coefficients-d_778.
html. How the value N is determined by component mass and dynamic force analysis should be
explained and that the resulting force F is a force that has to be overcome to make the mechanism
move.
Unit 3 LO5
OCR LEVEL 3 CAMBRIDGE TECHNICALS IN ENGINEERING
See Lesson Element Balancing
of rotating masses
ELECTRICAL, MECHANICAL, HYDRAULIC AND PNEUMATIC CONTROL
Title of suggested activity
OCR LEVEL 3 CAMBRIDGE TECHNICALS IN ENGINEERING
SUGGESTED ACTIVITIES
LO No:
2
LO Title:
Understand the electrical elements of control systems
Title of suggested activity
Suggested activities
Suggested timings
Also related to
The role of sensors and
actuators in a control system
Teachers could refer to work done on sensors and actuators covered in LO2 of Unit 7. Teachers might
also refer back to the example of the closed loop motor control in LO1 of Unit 14, and identify the
sensor and the actuator. Explain that Sensors provide electrical signals about the condition of a
system. Explain the role of electrical actuators to convert electrical energy into mechanical force.
Teachers could further relate these to industrial applications.
2 hours
Unit 7 LO2
Unit 14 LO1
Common types of electrical
actuators
Building from the work of LO1 on mechanical elements, teachers could explain that actuators are
predominantly linear or rotary. Teachers could use a variety of manufacturers data catalogues to show
the range of electric powered actuators available and their principles of operation.
3 hours
Unit 15 LO1
Motor types
Teachers could explain that motors are either ac or dc powered, and go on to explain the subsets in
each of these Web based resources such as http://electrical4u.com/types-of-dc-motor-separatelyexcited-shunt-series-compound-dc-motor/ for dc motors and http://electrical4u.com/inductionmotor-types-of-induction-motor/ and http://electrical4u.com/synchronous-motor-working-principle/
for ac motors, can be used to explain their principles of operation.
4 hours
Teachers can further introduce two special types of motor commonly used in machine control namely
servo motors and stepper motors. Web based resources such as http://electrical4u.com/servo-motorservo-mechanism-theory-and-working-principle/ and http://electrical4u.com/bipolar-stepper-motor/
ELECTRICAL, MECHANICAL, HYDRAULIC AND PNEUMATIC CONTROL
Learners could look at the resources and produce a presentation that outlines useful applications for
the different motor types.
Motor control
Teachers could explain control methods for different types of motors. As servo motors are commonly
used in robotics and other automation applications it may be useful to look at the control using pulse
width modulation. Teachers can recap the material covered in Unit 14 and relate it to the application
for servo motor control.
3 hours
Energy losses in electrical
actuators
Teachers should introduce the concept of efficiency losses and sources, i.e. friction, resistance in
windings, eddy current, hysteresis.
2 hours
Motor selection
Teachers should bring the work on motor types, motor control and energy losses together to look
at selection of motors for different applications. Learners could produce work specifying motors for
given applications of power, speed/torque, duty cycle.
3 hours
Unit 14 LO1
10
LO No:
3
LO Title:
Understand simple hydraulic systems
Title of suggested activity
Suggested activities
Power sources for hydraulic
systems
Teachers could introduce this element by explaining the fundamentals of pneumatic and hydraulic
5 hours
fluid power systems. That fluids under pressure can be used to transmit energy, and that
pressure = force/area, and that for a static fluid the pressure is exerted uniformly. For hydraulic systems
the fluid being a liquid, typically oil, which is incompressible. Teachers could show either with practical
experiments or using videos how hydraulic systems operate. Hydraulics and Pneumatics by Parr is
a useful text. ISBN: 9780080966748 http://www.amazon.co.uk/Hydraulics-Pneumatics-TechniciansEngineers-Guide/dp/0080966748
Suggested timings
Web based resources such as the following website may also prove useful https://www.youtube.com/
watch?v=YlmRa-9zDF8
Also related to
ELECTRICAL, MECHANICAL, HYDRAULIC AND PNEUMATIC CONTROL
SUGGESTED ACTIVITIES
Teachers can explain hydraulic systems range from simple systems such as a car jack or a brake
system to pumped industrial systems. Pumped systems taking the oil from a reservoir. The flow of
oil can then be controlled by valves to direct it to actuators, and is then returned to the reservoir.
Web based resources such as the following website may prove useful https://www.youtube.com/
watch?v=kzqkPx8F3D8
Valves and actuators for
hydraulic systems
Teachers can explain that valves are control elements to control the flow of hydraulic fluid around a
circuit. Teachers can explain the principal types of valves and their applications. These would include
spool or shuttle valves, poppet valves, check valves, and pilot valves. Hydraulics and Pneumatics
by Parr is a useful text. Physical hardware or web based resources such as videos or manufacturers
catalogues may better illustrate current designs used in industrial applications.
Teachers can explain that actuators convert the energy in compressed fluid into motion. The two
principle classes of linear and rotary actuators should be explained. The principles of operation of
single acting, double acting multi stage actuators could be explained. Again Parr is a useful text as
well as web based resources such as videos or manufacturers catalogues.
11
5 hours
OCR LEVEL 3 CAMBRIDGE TECHNICALS IN ENGINEERING
Teachers can explain the differences between hydrostatic and hydrodynamic pump types. These
could include types in common use in industrial applications such as gear pumps, vane pumps, and
axial and rotary piston pumps.
OCR LEVEL 3 CAMBRIDGE TECHNICALS IN ENGINEERING
Title of suggested activity
Suggested activities
Suggested timings
Also related to
Fluid transmission in
hydraulic systems
Learners should be introduced to graphical representation of hydraulic circuits to relevant standards
(e.g. ISO 1219-1:2012). Teachers could relate the synergy with electrical wiring diagrams, and explain
the basic symbols used to represent common hydraulic components. Learners could draw simple
hydraulic circuits to perform specified hydraulic requirements, drawing appropriate symbols and
connecting them for correct operation. Teachers could use the ISO standard for reference, or free
online web resources from hydraulics suppliers such as http://hydraulicspneumatics.com/othertechnologies/chapter-4-iso-symbols
4 hours
Unit 2 LO5
Teachers could then expand this theoretical arrangement to look at practical issues of fluid flow in
terms of volume flow rate, pressure and velocity. Teachers could introduce the equation:
power = pressure × volume flow rate(Q)
for determining the required pump size for the application.
Teachers can then look at pipe sizing using nomograms. A useful web based resource allows learners
to calculate pipe sizes for required applications http://www.insanehydraulics.com/library/hosesizing.
html
Teachers could then introduce concepts of laminar and turbulent flow from modules in engineering
science. The issue of transmission losses and pressure drop could be introduced and that this is
proportional to the square of the volume flow rate.
ELECTRICAL, MECHANICAL, HYDRAULIC AND PNEUMATIC CONTROL
See Lesson Element Fluid
transmission in hydraulic
systems
Teachers could develop this further to look at the power losses and how this lost power transforms
to heat within the fluid system. Teachers could use the example of boiling fluid within a hydraulic
braking system to illustrate how and why this is undesirable.
12
LO No:
4
LO Title:
Understand simple pneumatic systems
Title of suggested activity
Suggested activities
Suggested timings
Similarities and differences
with hydraulic systems
Teachers could explain the similarities between both systems i.e. that both use a compressed fluid
to transmit power, and both use similar graphical representation symbols, and similar control and
actuator elements. The differences should also be explained, particularly that pneumatics uses a gas,
which is a compressible fluid. Teachers can explain that air is a reasonable approximation of an ideal
gas and can thus operate in accordance with the ideal gas laws. Parr is a useful text.
3 hours
Teachers should highlight how the differences between gas and liquid in a fluid power system
make Hydraulic and pneumatic systems more applicable for specific applications. When Learners
understand the differences they should be able to identify which systems are most appropriate for
specific applications.
Compressors for pneumatic
systems
Teachers could explain the two classes of compressors for pneumatic systems, i.e.:
• dynamic (e.g. centrifugal, axial)
• positive displacement (e.g. rotary, reciprocating)
Also related to
ELECTRICAL, MECHANICAL, HYDRAULIC AND PNEUMATIC CONTROL
SUGGESTED ACTIVITIES
3 hours
Hydraulics and Pneumatics by Parr is a useful text. Web resources such as http://www.
engineeringtoolbox.com/air-compressor-types-d_441.html can also be used to look at practical issues
with compressors for industrial applications.
Valves and actuators for
pneumatic systems
There is a lot of commonality between this and the section in LO3 for hydraulic valves and actuators.
Teachers can build upon this but highlight the differences. Web resources such as http://resources.
norgren.com/document_resources/USA/Simplified%20Valve%20Circ%20Guide.pdf. can be used to
illustrate the range of valves.
Fluid transmission in
pneumatic systems
Again, there is close similarity between graphical representation of hydraulic and pneumatic circuits,
3 hours
and the same ISO standard is used for representation of both. Teachers could highlight the differences
in symbols to identify pneumatic components and explain where circuit layout will differ.
Transmission losses in pneumatic systems can be explained. Calculations for pressure drops and
pipe sizing can be made. Web resources such as the following are a useful resource http://www.
engineeringtoolbox.com/pressure-drop-compressed-air-pipes-d_852.html
Moisture build up in pipe
Teachers could compare the closed system nature of a fluid in a hydraulic circuit with the open system 2 hours
networks and need for drains nature of pneumatics where air is taken from and returned to atmosphere. Teachers should explain
how air contains moisture depending upon atmospheric conditions, measured as humidity. This
moisture can condense in pneumatic systems. Practical measures such as drains and drying elements
within the system should be explained. Web resources such as http://www.smcworld.com/docs/
technological_material/en/pdf/P-E01-11B-condensation.pdf may be useful.
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OCR LEVEL 3 CAMBRIDGE TECHNICALS IN ENGINEERING
3 hours
ELECTRICAL, MECHANICAL, HYDRAULIC AND PNEUMATIC CONTROL
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