gce a2 level exemplifying examination performance

Exemplifying Examination PerformanceTechnology and Design

GCE A2 LEVEL

For first teaching from September 2008

This is an exemplification of candidates’ performance in A2 examinations (Summer Series 2010) to support the teaching and learning of the Technology and Design

1CCEA EXEMPLIFYING EXAMINATION PERFORMANCE

A2 Technology & Design

Introduction

These materials illustrate aspects of performance from the 2010 summer A2 examination series of CCEA’s revised GCE Specification in Technology and Design.

Students’ grade A responses are reproduced as written in the examination. They are accompanied by commentaries written by senior examiners. The commentaries draw attention to the strengths of the students’ responses and indicate, where appropriate, how improvements could be made.

The materials exemplify the standard for the lifetime of the specification. It is intended that they should provide a benchmark of candidate performance and help teachers and students to raise standards.

The texts included for exemplification are dependent on the questions chosen by candidates in the summer 2010 examination series.

For further details of our support package, please visit our website at www.ccea.org.uk

Best wishes

Judith RyanEducation Manager, Technology & DesignEmail: [email protected]: 028 9026 1200 (ext. 2200)

EXEMPLIFYING EXAMINATION PERFORMANCE

CCEA EXEMPLIFYING EXAMINATION PERFORMANCE2


TIME2 hours.

INSTRUCTIONS TO CANDIDATES

5827

ADVANCEDGeneral Certificate of Education

2010

Technology and DesignAssessment Unit A2 1

assessingSystems and Control

[AV211]

FRIDAY 28 MAY, MORNING

AV

211

New

Specification

INFORMATION FOR CANDIDATESThe total mark for this paper is 80, including a maximum of 4 marks for quality of written communication.Marks for quality of written communication will be awarded for questions 2(c)(iii) and 3(c).Figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question.

Write your Centre Number and Candidate Number on the Answer Booklet provided and on the A3 pro forma answer pages provided.Answer either the two questions in Section A or the two questions in Section B.Answers to questions 1(e), 2(c)(ii), 3(a)(iii), 3(b), 3(e), 4(b), 4(c) and 4(d) should be made on the A3 pro forma answer pages provided.At the conclusion of the examination, attach the A3 pro forma answer pages securely to the Answer Booklet with the treasury tag supplied.

4 CCEA EXEMPLIFYING EXAMINATION PERFORMANCE5827 2 [Turn over

Answer either the two questions in Section A or the two questions in Section B.

Section A

Electronic/Microelectronic Systems

1 A block diagram for a soil heating system for a greenhouse is shown in Fig. 1(a). The heating elements are controlled by a switch unit which in turn can be programmed

using the time clock module.

INPUTTime ClockModule

CONTROLElectricalSwitch Unit

OUTPUTHeatingElements

Fig. 1(a)

(a) (i) Explain why the system shown in Fig. 1(a) is an open loop control system. [2]

(ii) Redraw the block diagram shown in Fig. 1(a) modifying it to become a closed loop system and describe the function of any additional blocks. [3]

(iii) The time clock module and electrical switch unit which operate at 5 volts are electrically isolated from the high voltage heating elements using an optical switch. Explain with the aid of a diagram how this is achieved. [4]

(b) Views of a concept design for an electronic planting aid to set the distance between plant seeds is shown in Fig. 1(b). As the device is pushed over the soil, a sound is to be emitted to indicate to the user that a seed is to be planted.

The input to the electronic system is based on a disc with notches which will activate a microswitch. The disc is fixed to the rubber wheel.

Fig. 1(b)

Name and draw a method other than a mechanical switch to detect the rotation of the disc. [3]

sound

Handle

rubber wheel

Position ofmicroswitchDisc

withnotches

5827 3 [Turn over

(c) The initial circuit to be used in the planting aid is a PIC-based circuit as shown in Fig. 1(c).

Fig. 1(c)

(i) With the aid of a circuit diagram explain how a microswitch could be used in conjunction with a resistor to provide a digital input to the PIC shown in Fig. 1(c). [4]

(ii) Every time a notch on the disc passes under the microswitch, the PIC circuit shown in Fig. 1(c) must produce an output pulse with a duration of 0.2 seconds to drive the buzzer and indicate that a seed should be planted. Write a flowchart program which will achieve this. [4]

(iii) If the rubber wheel on the system shown in Fig. 1(b) is rotated too quickly, some of the notches may not be detected. Calculate the maximum allowable revolutions per minute (RPM) of the wheel if the PIC circuit in Fig. 1(c) produces an output pulse with a duration of 0.2 seconds. [3]

5 V

0 V

0 V

V+

Input 1

Output 1

PIC

5CCEA EXEMPLIFYING EXAMINATION PERFORMANCE5827 2 [Turn over


Section A

Electronic/Microelectronic Systems

1 A block diagram for a soil heating system for a greenhouse is shown in Fig. 1(a). The heating elements are controlled by a switch unit which in turn can be programmed

using the time clock module.

INPUTTime ClockModule

CONTROLElectricalSwitch Unit

OUTPUTHeatingElements

Fig. 1(a)

(a) (i) Explain why the system shown in Fig. 1(a) is an open loop control system. [2]

(ii) Redraw the block diagram shown in Fig. 1(a) modifying it to become a closed loop system and describe the function of any additional blocks. [3]

(iii) The time clock module and electrical switch unit which operate at 5 volts are electrically isolated from the high voltage heating elements using an optical switch. Explain with the aid of a diagram how this is achieved. [4]

(b) Views of a concept design for an electronic planting aid to set the distance between plant seeds is shown in Fig. 1(b). As the device is pushed over the soil, a sound is to be emitted to indicate to the user that a seed is to be planted.

The input to the electronic system is based on a disc with notches which will activate a microswitch. The disc is fixed to the rubber wheel.

Fig. 1(b)

Name and draw a method other than a mechanical switch to detect the rotation of the disc. [3]

sound

Handle

rubber wheel

Position ofmicroswitchDisc

withnotches

5827 3 [Turn over

(c) The initial circuit to be used in the planting aid is a PIC-based circuit as shown in Fig. 1(c).

Fig. 1(c)

(i) With the aid of a circuit diagram explain how a microswitch could be used in conjunction with a resistor to provide a digital input to the PIC shown in Fig. 1(c). [4]

(ii) Every time a notch on the disc passes under the microswitch, the PIC circuit shown in Fig. 1(c) must produce an output pulse with a duration of 0.2 seconds to drive the buzzer and indicate that a seed should be planted. Write a flowchart program which will achieve this. [4]

(iii) If the rubber wheel on the system shown in Fig. 1(b) is rotated too quickly, some of the notches may not be detected. Calculate the maximum allowable revolutions per minute (RPM) of the wheel if the PIC circuit in Fig. 1(c) produces an output pulse with a duration of 0.2 seconds. [3]

5 V

0 V

0 V

V+

Input 1

Output 1

PIC


(d) An addition to the circuit for the planting aid is shown in Fig. 1(d) where the output from the PIC circuit in Fig. 1(c) is connected to the input (clk) pin of a BCD counter. A 7-segment display will provide a visual indication of the number of seeds that should have been planted in a row.

Fig. 1(d)

(i) State the function of the BCD to 7-segment decoder in the circuit shown in Fig. 1(d). [2]

(ii) Explain why a BCD counter is more appropriate for this application than a binary counter. [3]

(iii) Show with the aid of a circuit diagram how the BCD counter shown in Fig. 1(d) can be reset. [2]

(e) Using electronic circuit diagrams on the blank pro forma provided (answer number 1(e)), show how the following could be achieved.

• Count and display up to a maximum of 99, the number of seeds planted. • A means to enable the user to alter the distance between the planting of seeds.

[10]

5 V

From PICcircuit

to BCD to 7 segment decoderand 7 segment display

BCDCounter

Clk

Reset

0 V


2 The voltage divider circuit shown in Fig. 2(a) is to be used as part of a circuit for measuring the temperature of water in a storage tank. The resistance/temperature characteristic for the thermistor Rth is also shown.

Fig. 2(a)

(a) (i) State the main physical property of a thermistor for this application. [1]

(ii) State the purpose of the voltage divider arrangement shown in Fig. 2(a). [1]

(iii) If the water temperature varies between 5 °C and 15 °C, calculate the voltage Vo for both these temperatures. [4]

(iv) Calculate the total power dissipated by R1 and Rth at 20 °C. [2]

(v) Suggest one practical advantage of replacing the fixed resistor in Fig. 2(a) with a variable type resistor. [2]

00 10 0 200 300

( OC)

Rth

10

8(kΩ)

6

4

6V

0V

R1 1.2 kΩ

Rth

temp

Vo


(b) The output voltage Vo from the voltage divider in Fig. 2(a) is to be connected to a 10-segment LED bar array and driver as shown Fig. 2(b), where each segment is to represent 1 °C. In order for this to happen, the output voltage Vo from the voltage divider must be amplified by a factor of 40.

Fig. 2(b)

(i) Describe the function of a bar array driver. [2]

(ii) Design an amplifier, based on an op amp to match the voltage divider output from Fig. 2(a) to the input of the display driver and show how it would be connected to the circuit shown in Fig. 2(b). [2]

(iii) Suggest suitable resistor values for the amplifier in part (b)(ii) given that the gains of inverting and non-inverting amplifiers are – Rf/R1 and 1 + Rf/R1 respectively where resistor Rf is the feedback resistor. [3]

10 V

0 V

–10 V

Fromamplifier

LEDbararray

Bararraydriver


(c) A PIC based circuit could be used to measure and display the level of water in the storage tank. A float attached to a rotary potentiometer could be used to detect the water level. The PIC shown in Fig. 2(c) has five input ports (i/p 0–i/p 4) and eight output ports (o/p 0–o/p 7).

Fig. 2(c)

(i) The input ports on the PIC shown in Fig. 2(c) can function as either digital or analogue inputs. Briefly explain the difference between these two types of input. [2]

(ii) The voltage range of the analogue port on the PIC shown in Fig. 2(c) is from 0 V to 6 V with a corresponding digital range from 0 to 255.

Using electronic circuit diagrams on the blank pro forma provided (answer number 2(c)(ii)), design a circuit based on the float system and PIC shown in Fig. 2(c) and write a flow chart program to fulfil the following:

• determine the water level using the potentiometer on i/p 1. • display the level on seven LEDs o/p 0–o/p 6 where o/p 0 indicates that the tank

is empty and o/p 6 indicates that the tank is full. Outputs indicate equidistant input levels in the tank.

• open a high voltage water valve connected to o/p 7 to allow the tank to refill when the tank is empty.

• switch off the water valve when the tank is full. [12]

(iii) PIC microcontrollers are a common choice for pupils who want to design and make control circuits for project work. Describe two main features of PICs that have made them so popular for project work, illustrating your answer with examples. Justify choosing a hard wired solution in preference to a PIC for certain applications. [5]

Quality of written communication [4]

Wateroutlet

Waterinletvalve

Float

Rotarypotentiometer

PIC

o/p7

o/p6

o/p5

o/p4

o/p3

o/p2

o/p1

i/p4

i/p3

i/p2

i/p1

i/p0 o/p

0



Section B

Mechanical and Pneumatic Control systems

3 Fig. 3(a) shows a cam and follower to be used as part of a prototype mechanical system. The cam rotates in a clockwise direction and the roller follower is offset to the right of the cam centre line by 10 mm.

(a) (i) Name and sketch one other follower, apart from a knife edge or roller, which can be used with cams. [2]

(ii) The cam rotates at 120 rev/min with a torque of 1.75 Nm. Calculate the power expended. [3]

(iii) On the pro forma provided (answer number 3(a)(iii)), construct a performance/displacement diagram which would accurately produce the following motion:

• 0–120 rise 60 mm with uniform acceleration and retardation • 120–180 rise 20 mm with uniform velocity • 180–360 fall 80 mm with simple harmonic motion. [5] A scale of 1 mm = 1 mm should be used

(b) On the pro forma provided (answer number 3(b)), using appropriate formal drawing techniques, construct a cam profile which would accurately follow the performance/displacement diagram as shown in Fig. 3(b). The diameter of the offset roller follower is 10 mm and the minimum cam diameter is 25 mm. Your answer may be drawn to a suitable scale. [10]

(c) A gearbox which provides the drive/motion for the cam uses a lubricant with a specific classification. Explain how lubricants are classified, discuss the mechanics of lubrication and viscosity and the factors to be considered when justifying the choice of a lubricant for a particular application. [5]

Quality of written communication [4]

(d) A universal joint has been used to transmit motion from the gearbox to the cam. Describe one main problem which is likely to be encountered during operation and suggest a solution. [1]

(e) In addition, Fig. 3(a) shows a pair of wheels which are to be used in conjunction with the cam and follower. On the blank pro forma provided (answer number 3(e)) design and draw a mechanical system which would achieve each of the following requirements:

• A gearing system which will allow a change in the direction of the wheels’ rotation when required as the motor only turns in the one direction.

• A manually activated system which will engage and disengage the transmission of motion from the motor to the rest of the system. [10]

5827 9 [Turn over

Fig. 3(a)

Wheel

Wheel

Cam

Roller follower

0 90 180

270 360

Angular rotation/degrees

Displacement

72 mm

Fig. 3(b)


Fig. 3(a)

Wheel

Wheel

Cam

Roller follower

0 90 180

270 360

Angular rotation/degrees

Displacement

72 mm

Fig. 3(b)


4 (a) (i) Briefly describe three safety issues associated with using pneumatic components. [3]

(ii) The work done by a single acting cylinder during the outstroke is 785 J. The cylinder has a stroke length of 100 mm and is supplied with an air pressure of 1 N/mm2. Calculate the diameter of the piston. Assume p = 3.14. [3]

(b) Fig. 4(a) shows part of a pneumatic-based production line used to stamp and sort boxes according to their size.

The following sequence begins when a solenoid Start valve receives an electrical signal which not only activates the sequence, but switches on the conveyor belts:

• Cylinder A outstrokes to close the gate. • Cylinder B outstrokes and stamps the underside of the box. • Cylinder B instrokes. • Cylinder C outstrokes slowly to push the box on to the lower conveyor belt. • Cylinder C instrokes. • Cylinder D instrokes once the box activates the Air Bleed to open the trap door. • Cylinder A instrokes. • Cylinder D outstrokes.

On the pro forma provided (answer number 4(b)), draw a suitable interlocking/cascade sequential pneumatic circuit to achieve the desired sequence. [16]

(c) Fig. 4(b) shows a single acting cylinder Q which is to be used to stamp rejected boxes at a further stage in the production line.

On the pro forma provided (answer number 4(c)), add any necessary components and piping to enable the cylinder to be operated with valve Y having the option of using valve X when a larger air pressure is required. When valve X is activated, air from an already activated valve Y may need to be blocked. [6]

(d) On the blank pro forma provided (answer number 4(d)), design and draw a pneumatic system which will stamp and remove oversized boxes (box 3) from the upper conveyor belt.

The system should • Detect the box, generate a signal to stop the motorised conveyor, then wait a few

seconds before stamping the box. • After completing the stamping, the box should be pushed to the side of the upper

conveyor belt slowly. [12]


Fig.

4(a

)

Air

blee

d

Trap

doo

r

Cyl

inde

r D

Chu

te

Low

erco

nvey

or b

elt

Ga

te Box

1

Box

2B

ox 3

Cyl

inde

r C

Cyl

inde

r A Upp

erco

nvey

or b

elt

Cyl

inde

r B


Fig.

4(a

)

Air

blee

d

Trap

doo

r

Cyl

inde

r D

Chu

te

Low

erco

nvey

or b

elt

Ga

te Box

1

Box

2B

ox 3

Cyl

inde

r C

Cyl

inde

r A Upp

erco

nvey

or b

elt

Cyl

inde

r B

5827 12 [Turn over

X

Q

Y

Fig. 4(b)

16 CCEA EXEMPLIFYING EXAMINATION PERFORMANCE

THIS IS THE END OF THE QUESTION PAPER


THIS IS THE END OF THE QUESTION PAPER

A2 1 (AV211):

Technology & Design: Student Responses


Examiner’s Comments

Q1 (a) (i) The response is correct and to the point.

(ii) The response provides a diagram with no description of the function of the additional blocks.

(iii) The response provides an acceptable diagram and explanation.

(b) The response provides a name and drawing of an alternative method.

(c) (i) The response provides a circuit diagram and explanation of the required signal input.

(ii) The flowchart provides an adequate response to the question.

(iii) The calculation of the maximum allowable revolution of the wheel is clearly laid out and correct.

(d) (i) The response is incorrect.

(ii) The response does not provide a clear reason as to why the BCD counter is preferable to the binary counter in this application.

(iii) The response does not show how the BCD counter can be reset using a negative edge trigger as indicated in Fig 1(d). The outputs indicated in the response are incorrect. Some credit has been given for the attempt made by the candidate.

(e) The response goes some way towards showing how counters would be cascaded to provide the required function. The response does not address the issue of altering the distance between planting of seeds satisfactorily.

Q2 (a) (i) The response is correct and explains the main physical property of the thermistor which is being utilised.

(ii) The response is correct and explains the purpose of the voltage divider circuit.

(iii) The response provides one correct calculation of the voltage Vo at 5oC. However, the response for the voltage at 15oC does not substitute the correct values for the resistances required to provide a correct answer

(iv) There is no response.

(v) There is no response.

(b) (i) The response does not provide a clear explanation of the function of the bar array driver.

(ii) The response is correct.

(iii) The response manipulates the equation for gain correctly and provides satisfactory values for the resistors.

(c) (i) The response provides a satisfactory explanation of the difference between the two types of signal.

(ii) The response is for the most part correct. The potentiometer output is connected to i/p0 rather than i/p1 which is a minor mistake. There is no lead connected to o/p0, however the circuit as drawn is acceptable. The program turns on the water supply when the tank is completely empty and not at any other possible level at the start of measurement of

A2 1 Technology & Design


the level. However, the response shows a degree of understanding of the problem and the issues to be addressed in its solution.

(iii) The response describes several features including the widely regarded main ones as to why PICs are used in project work with examples quoted. The description of a situation where a hard-wired solution may be preferable is satisfactory. The response has been couched in a form which employs appropriate language and use of spelling and grammar.



Q1 (a) (i) The response is correct.

(ii) The response provides a satisfactory diagram and explanation of the additional block.

(iii) The response does not address the use of the optical switch.

(b) The response names an alternative method of detection. The diagram provided is inadequate.

(c) (i) The diagram and explanation provided are satisfactory.

(ii) The flowchart provided goes some way to addressing the question. The output should have a duration of 0.2 seconds. The output in the response remains on.

(iii) The calculation of the maximum allowable revolutions of the wheel is correct

(d) (i) The response is correct.

(ii) The response is incorrect.

(iii) The response is incorrect.

(e) The response states the need for two counters to count up to 99 but does not indicate how this could be realised. In response to the second bullet point a possible solution is suggested but is not developed in a meaningful way.

Q2 (a) (i) The response is correct and explains the main physical property of the thermistor which is being utilised.

(ii) The response is correct and explains the purpose of the voltage divider circuit.

(iii) The response provides correct interpretation of the resistance values and their manipulation in the calculation of Vo for both temperatures.

(iv) The response shows that the correct thermistor value has been deduced and the correct formula for power has been applied. The method used is flawed leading to an incorrect answer.

(v) The response is acceptable.

(b) (i) The response does not provide a clear explanation of the function of the bar array driver.

(ii) The diagram provided is correct except for one error in the placement of the un-marked resistor.

(iii) The response manipulates the equation for gain correctly and provides satisfactory values for the resistors.

(c) (i) The explanation and accompanying diagram for a digital signal is correct but the diagram provided for an analogue signal is incorrect.

(ii) The response provides a solution to most aspects of the problem. The circuit diagram contains an error in the connection of the diode. The program turns on the water supply when the tank is completely empty but not at other levels below the maximum when initially measured. The intervals at which the various outputs are switched are flawed. However, the majority of aspects of the problem have been addressed in a satisfactory manner.



(iii) The response describes two main features illustrating why PICs are used in project work with examples quoted. There is an attempt to explain a situation where a hard-wired solution may be preferable. The response has been presented in a form which employs appropriate language and use of spelling and grammar.




(ii) The angular velocity has been calculated wrongly and the answer is incorrect. Equation partially correct.

(iii) The response is well drawn and correct.

(b) The response is, for the most part, correct but contains inaccuracies. Re-drawing the performance displacement diagram may have helped to eliminate inaccuracies..

(c) The response provides a satisfactory explanation of the classification of lubricants, the mechanics of lubrication and viscosity and the factors to be considered when justifying the choice of a lubricant for a particular application. The response uses appropriate language and grammar.

(d) The response is satisfactory.

(e) The response is inadequate.

Q4 (a) (i) The response provides three satisfactory safety issues associated with using pneumatic components.

(ii) The equations used, the calculation and the answer provided are correct.

(b) The response addresses most aspects of the problem. However, certain aspects e.g. the slow outstroke of C and linking of the change-overs is incorrect.

(c) The response addresses the major part of the question. The piping of the air operated 3 port valve is incorrect. (d) This response addresses the major aspects of the problem. Issues concerning the time delay before stamping the box and the removal of the box from the upper conveyor belt slowly, need refinement. The five port valves can act in one direction only and the valve used to activate the removal of the box needs more drawing detail.





(ii) The equation, calculation and answer are correct.

(iii) The response is well drawn and correct.

(b) The response is well drawn and correct.

(c) The response provides a justification for the choice of a lubricant with a limited discussion of the concept of viscosity and the classification of lubricants. The language used is appropriate but the grammar employed is erratic.

(d) The response is satisfactory.

(e) The response contains an attempt to draw a single plate clutch with no relation to the system referred to in the question. The first bullet point of the question has not been addressed.

Q4 (a) (i) The response provides three satisfactory safety issues associated with using pneumatic components.

(ii) The initial calculation of force is incorrect although corrected on a subsequent line. The equation for pressure is wrong and the resulting answer is incorrect.

(b) The response addresses most aspects of the problem. However, certain aspects e.g. the slow outstroke of C and the use of the air bleed have not been addressed.

(c) The response addresses the OR logic aspect of the question. However, the activation of valve X blocking air from valve Y is not addressed.

(d) This response addresses most of the major aspects of the problem. The process of stopping the motorised conveyor belt, however, needs to be addressed.


gce a2 level exemplifying examination performance

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