National Quali cations EXEMPLAR PAPER ONLY

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1 FOR OFFICIAL USE H National Quali cations Mark EXEMPLAR PAPER ONLY EP13/H/01 Engineering Science Date Not applicable Duration 2 hours *EP13H01* Fill in these boxes and read what is printed below. Full name of centre Town Forename(s) Surname Number of seat Date of birth Day Month Year Scottish candidate number Total marks 90 SECTION 1 20 marks Attempt ALL questions. SECTION 2 70 marks Attempt ALL questions. Write your answers clearly in the spaces provided in this booklet. Additional space for answers is provided at the end of this booklet. If you use this space you must clearly identify the question number you are attempting. Numerical answers should include units, and be rounded to an appropriate number of significant figures. Show all working and units where appropriate. You should refer to the Higher Data Booklet which you have been given. Use blue or black ink. Before leaving the examination room you must give this booklet to the Invigilator; if you do not, you may lose all the marks for this paper. *EP13H0101*

2 SECTION 1 20 marks Attempt ALL questions 1. The circuit shown below is being designed by an electronic engineer, to switch on a heated seed tray when the temperature falls to 15 ºC. +12 V 100 kω heating element 12 V 100 ma Type 2 thermistor 0 V (a) At 15 ºC, with the transistor switched on and saturated, the resistance of the thermistor is 8 kω and the current through the 100 kω resistor is ma. Calculate: (i) the current flowing through the thermistor; 1 (ii) the current flowing into the base of the transistor. 1 (b) The heating element is rated at 12 V, 100 ma. Calculate the minimum current gain h FE required for the heating element to fully switch on at 15 ºC. 2 *EP13H0102* Page two

3 2. An electronic control system keeps the wind turbine (shown below) facing into the wind. The wind direction is sensed by a wind vane connected to a potentiometer. The signal from the potentiometer is compared with a reference voltage, and the turbine head is rotated by a motor to face the wind. As the turbine head moves closer to the wind direction, the motor slows and then comes to rest. Wind direction Turbine head Wind vane (a) State the full name of the type of control used. 1 (b) State which configuration of operational amplifier would be used in this electronic control system. 1 (c) Complete a circuit diagram for this electronic control system. Show all components and connections V output to motor driver 0 V *EP13H0103* Page three

4 3. A structural engineer is experimenting with two materials. The dominant mechanical property of specimen A is brittleness, and of specimen B is ductility. Sketch, on the same axes, typical stress-strain graphs for specimen A and specimen B. Clearly label the axes and identify each graph. 3 *EP13H0104* Page four

5 4. A large distribution warehouse for an online marketing company is being planned. The facility is to be largely automated as shown below. A civil engineer has been asked to outline some of the social and economic impacts this may have on the local community. Describe one positive and one negative social impact, and one beneficial and one harmful environmental impact that the project might have locally. 4 Positive social impact Negative social impact Beneficial environmental impact Harmful environmental impact *EP13H0105* Page five

6 5. The figure below shows a production line for filling and capping bottles. A lid-fitting device (Z) operates when an ultrasound sensor (A) or a load cell (B) detects that the bottle is full, and a filling-nozzle sensor (C) detects that filling has stopped. C A B Z Transducer light sensor (A) load cell (B) filling-nozzle sensor (C) lid-fitting device (Z) State 1 = bottle full 1 = bottle full 0 = filling stopped 1 = fit lid Write a Boolean expression for the output Z, in terms of the three inputs A, B and C. 2 *EP13H0106* Page six

7 6. The motorised pump shown produces the following performance data, when tested by a maintenance engineer. Energy output: 97 J in 5 seconds Current drawn: 3 0 A Voltage: 12 A PUMP Draw an energy audit diagram for the pump, showing its efficiency. 3 *EP13H0107* Page seven

8 SECTION 2 70 marks Attempt ALL questions 7. Tests are to be carried out on the supports of one of the seating units, of the fairground swing shown below. A structural engineer is designing the seating, cabling and supports for the fairground swing. (a) (i) Describe examples of how an engineer could apply relevant engineering knowledge and skills, to determine appropriate shapes and dimensions for components of the swing. 4 (ii) Explain how an engineer would apply a factor of safety in the design of the cables and supports. 2 *EP13H0108* Page eight

9 7. (continued) A simplified free-body diagram of the supporting unit, for a particular loading condition of the seat, is shown. 790 N F θ X 12 Z Y V 290 N (b) Calculate: (i) the magnitude of the forces in members XY, YZ and XZ; 5 *EP13H0109* Page nine

10 7. (b) (continued) (ii) the magnitude of the forces V and F. 4 *EP13H0110* Page ten

11 8. An electrical engineer is designing a small-scale community-based hydroelectric scheme. It will use the water in a river to turn a turbine and generator. The turbine should turn at a constant speed. A tachogenerator on the turbine shaft generates a voltage proportional to the shaft speed. A control system processes this signal to control a motorised valve, which either increases or decreases water flow to the turbine, in order to control its shaft speed. (a) Draw a control diagram for this control system. Label all sub-systems. 6 *EP13H0111* Page eleven

12 8. (continued) The circuit shown gives a warning if the turbine speed is either too fast or too slow. +12 V R 3 V R3 op-amp V too slow warning lamp R 4 too fast warning lamp transistor 2 signal from tachogenerator R 2 V R2 0 V +12 V 0 V R 4 transistor 1 V tach R 1 V R1 op-amp 1 0 V (b) Explain the operation of the circuit shown above. 5 A warning lamp shows when the turbine speed varies by more than 5% (±0 15 V) from the output of 3 V. (c) The total resistance of the resistor ladder in the circuit above is 12 kω. Calculate appropriate values for resistors R 1, R 2, and R 3. 4 *EP13H0112* Page twelve

13 9. A structural and an electronic engineer are working together to develop a system, for use during routine maintenance of a nuclear reactor. The control rods are to be lifted from the containment vessel, using the robot arm shown below. joint 2 joint 3 joint 1 The joint 1 motor needs to be high powered and provide a high torque. The robot arm should rotate slowly about joint 1, at one of two speeds. The power to the joint 1 motor is controlled by a single pin from a microcontroller. During one test, the joint 1 motor received either 100% or 60% of the full power available, assuming no losses in the output driver. (a) (i) State the full name of the technique used to vary the power to an output device using a single pin of a microcontroller. 1 (ii) Draw a clearly labelled graph, showing how this technique could be used to control the joint 1 motor so that it runs at 60% of its full power. 2 *EP13H0113* Page thirteen

14 9. (continued) A MOSFET output-driver circuit provides current to the joint 1 motor. The graph below shows the operational characteristics of the output-driver circuit. Lines A, B, C, D, and E show the characteristics of the MOSFET for five different gate-source voltages (V GS ). Line F shows the characteristics of the motor. 1 0 A: V GS = 12 V 0 9 B: V GS = 10 V Drain Current I D (A) Drain-Source Voltage V DS (V) C: V GS = 8 V D: V GS = 6 V E: V GS = 4 V F: motor characteristics (b) For a signal of 4 V on the microcontroller output pin: (i) determine the Drain-Source Voltage; 1 (ii) determine the Drain Current; 1 (iii) calculate the power dissipated in the MOSFET. 2 *EP13H0114* Page fourteen

15 9. (continued) The engineer is selecting a drive mechanism for joint 1. She considers the following options: a simple gear train, a chain drive, a pulley drive, or a compound gear train. (c) Give two reasons why a compound gear train would be the most appropriate choice. 2 One section of the robot arm consists of a single member, as shown below, where it is rotated to the horizontal position. forearm 720 N pivot 8 º 110 º 77 º 900 N 4218 N 0 4 m 1 2 m 0 3 m (d) This member is made from tubular stainless steel. Give two reasons why this would be a suitable choice of material. 2 *EP13H0115* Page fifteen

16 9. (continued) (e) Calculate the magnitude and direction of the reaction at the pivot. 9 *EP13H0116* Page sixteen

17 10. The computer-controlled milling machine shown below uses a rotating head to cut multiple slots. A motor moves the cutter head horizontally in the x-axis into the correct position. Two pneumatic cylinders manoeuvre the cutter to cut the slot. Home x (+ve) y (+ve) z ( ve) *EP13H0117* Page seventeen

18 10. (continued) Cylinder Z moves the cutter down in the z-axis to make a hole in the work piece and then cylinder X moves the cutter in the x-axis to mill out a slot. Cylinder X then returns the cutter to the start of the slot and cylinder Z retracts the cutter up out of the work. To achieve this, the cylinders are controlled sequentially in the order Z+, X+, X, Z using the pneumatic circuit shown below. Cylinder Z Valve Z Valve 1 Valve 2 Cylinder X Valve X Valve 3 Valve 4 On/Off Valve Group Valve *EP13H0118* Page eighteen

19 10. (continued) (a) Describe, using appropriate terminology, how the circuit shown achieves the given sequence. 8 The system to move the cutter in the x-axis consists of a stepper motor, moving the cutter using a rack and pinion mechanism. A limit switch registers the cutter head Home position at the left-hand side of the x-axis. Before starting any new sequence, the cutter head always moves to its Home position (x = 0). Each time the stepper motor IC receives a pulse, the stepper motor moves through a fixed angle. A sub-procedure startpos_x moves the cutter head to the x-axis home position. Each time a pulse with MARK time of 1 ms is sent to the stepper motor driver IC, the cutter head moves 0 5 mm. (b) (i) Calculate the required SPACE time between stepper-driver pulses to move the cutter head at 25 mms 1. 2 *EP13H0119* Page nineteen

20 10. (b) (continued) (ii) Draw a flowchart to represent the sub-procedure startpos_x. 6 *EP13H0120* Page twenty

21 10. (continued) A combinational logic system controls the motor (M) according to the Boolean expression M = Z.Y.X + Z.Y.X The cutter motor is on when M = 1 The stepper motor moves the cutter in the x-axis when X = 1 The cylinder which moves the cutter in the z-axis outstrokes when Z = 1 The cylinder which moves the cutter in the y-axis outstrokes when Y = 1 (c) (i) Complete the truth table for M in terms of Z, Y and X. 3 Z Y X M (ii) State which of the signals X, Y and Z does not affect the state of M. 1 [END OF EXEMPLAR QUESTION PAPER] *EP13H0121* Page twenty-one

22 ADDITIONAL SPACE FOR ANSWERS *EP13H0122* Page twenty-two

23 ADDITIONAL SPACE FOR ANSWERS *EP13H0123* Page twenty-three

24 H EP13/H/01 National Quali cations EXEMPLAR PAPER ONLY Engineering Science Marking Instructions These Marking Instructions have been provided to show how SQA would mark this Exemplar Question Paper. The information in this publication may be reproduced to support SQA qualifications only on a non-commercial basis. If it is to be used for any other purpose, written permission must be obtained from SQA s Marketing team on permissions@sqa.org.uk. Where the publication includes materials from sources other than SQA (ie secondary copyright), this material should only be reproduced for the purposes of examination or assessment. If it needs to be reproduced for any other purpose it is the user s responsibility to obtain the necessary copyright clearance. *EP13H0124*

25 General Marking Principles for Higher Engineering Science This information is provided to help you understand the general principles you must apply when marking candidate responses to questions in this Paper. These principles must be read in conjunction with the detailed Marking Instructions, which identify the key features required in candidate responses. (a) Marks for each candidate response must always be assigned in line with these general marking principles and the detailed Marking Instructions for this assessment. (b) Marking should always be positive. This means that, for each candidate response, marks are accumulated for the demonstration of relevant skills, knowledge and understanding; they are not deducted from a maximum on the basis of errors or omissions. (c) Where a candidate makes an error at an early stage in a multi-stage calculation, credit should normally be given for correct follow-on working in subsequent stages, unless the error significantly reduces the complexity of the remaining stages. The same principle should be applied in questions which require several stages of non-mathematical reasoning. (d) All units of measurement will be presented in a consistent way, using negative indices where required, eg ms 1. Candidates may respond using this format, or solidus format (m/s), or words (metres per second), or any combination of these, eg metres/second. (e) Answers to numerical questions should normally be rounded to an appropriate number of significant figures. However, the mark can be awarded for answers which have up to two figures more or one figure less than the expected answer. (f) (g) Unless a numerical question specifically requires evidence of working to be shown, full marks should be awarded for a correct final answer (including unit) on its own. A mark can be awarded when a candidate writes down the relevant formula and substitutes correct values into the formula. No mark should be awarded for simply writing down a formula, without any values. (h) Credit should be given where a labelled diagram or sketch conveys clearly and correctly the response required by the question. (i) (j) Marks should be awarded regardless of spelling, as long as the meaning is unambiguous. Candidates may answer programming questions in any appropriate programming language. Marks should be awarded, regardless of minor syntax errors, as long as the intention of the coding is clear. (k) Where a question asks the candidate to explain, marks should only be awarded where the candidate goes beyond a description, for example by giving a reason, or relating cause to effect, or providing a relationship between two aspects. (l) Where separate space is provided for rough working and a final answer, marks should normally only be awarded for the final answer, and all rough working ignored. Page two

26 Marking Instructions for each question SECTION 1 Question Expected response Max mark Additional guidance 1 a i I th = V/R = 0 7/8 = ma 1 1 mark for answer with units. 1 a ii I b = = ma 1 1 mark for answer with units. 1 b h FE = 100/ = mark for substitution, 1 mark for answer. 2 a Closed loop proportional 1 2 b Difference 1 2 c 2 Each component below must have correct connections: difference amp with four resistors (1 mark) potential divider to inverting input (could be two resistors, one must be variable) and potential divider to non-inverting input (could be two resistors, one must be variable) (1mark) Page three

27 Question Expected response Max mark Additional guidance 3 3 Correct brittle trace, showing material fractures soon after leaving the elastic range. (1 mark) Correct ductile trace, showing a significant plastic range. (1 mark) Correctly labelled axes. (1 mark) 4 Positive social impact could include a description of: increased employment prospects improved training opportunities improved infrastructure Negative social impact could include a description of: traffic disruption disturbance due to noise Beneficial environmental impact could include a description of: improved energy efficiency in new development compared to old improved sustainability in the development 4 1 mark for describing a relevant positive social impact. 1 mark for describing a relevant negative social impact. 1 mark for describing a relevant beneficial environmental impact. 1 mark for describing a relevant harmful environmental impact. Note: descriptions are required, not simple statements. Harmful environmental impact could include a description of: loss of green belt more demand on water and power services Page four

28 Question 5 Z= (A+B).C or Z= A.B.C + A.B.C + A.B.C Expected response Max mark 2 1 for (A+B) 1 for.c Additional guidance (or 2 marks for the expanded equivalent, as shown) 6 3 P in = VxI = 12 x 3 = 36 W P out = E/t = 97/5 = 19 4 W Power lost = = 16 6 W input power 36 W or input energy 180 J pump system efficiency 54% output power 19 W or output energy 97 J or E in = VxIxt = 12 x 3 x 5 = 180 J E out = 97 J Energy lost = = 83 J waste power 17 W or waste energy 83 J efficiency = 19 4/36 (or 97/180) = 53 8% (answers shown to two significant figures) 1 mark for showing input power or energy and output power or energy on diagram. 1 mark for calculating efficiency. 1 mark for showing waste power or energy on diagram. Page five

29 SECTION 2 Question 7 a i Statements such as: Expected response The engineer could design the structure using nodal analysis, to keep stresses in members within the safe working stress of the material. The engineer could use the calculated stress, to determine appropriate dimensions for each member. The engineer would apply knowledge of the properties of materials, to influence the dimensions required and appropriate shapes for components. Any explanation of why particular shapes would be appropriate for different loadings, including tensile, compressive, bending, torsion, and shear. Design of shapes of components, to maximise strength-to-weight ratio. Selection of types of joints, depending on what that section of the structure had to do. 7 a ii The engineer would look up the ultimate or yield stress for their intended material. The member could then be designed to ensure the stress remained less than this stress by a factor. This factor (eg ensuring the working stress was never more than 1/3 of the ultimate stress), would depend on the environment in which the structure was to be located and the consequences of failure. Max mark Additional guidance 4 Any four valid relevant points, similar to those shown, exemplifying the application of engineering skill and/or knowledge relevant to the context. 2 Any two valid relevant points, showing the application of engineering skill and/or knowledge relevant to the context. Note: no mark should be awarded for a simple definition of factor of safety. Page six

30 Question Expected response 7 b i 5 Max mark Additional guidance From analysis of node Y, V XY = 290 (1 mark) Applying trigonometry to obtain answer for XY with units. (1 mark) From analysis of node Y, YZ = H XY (1 mark) Applying trigonometry to obtain answer for YZ with units. (1 mark) Applying trigonometry to obtain answer for XZ with units. (1 mark) Page seven

31 Question Expected response 7 b ii 4 Max mark Additional guidance 1 mark for answer (with units) for V 1 mark for components of 790 N 1 mark for answer (with units) for V F 1 mark for answer (with units) for F and θ Page eight

32 Question Expected response Max mark 8 a 6 1 mark each for: Additional guidance error detector (correct symbol and name) error amplifier (correct symbol and name) driver motor and/or valve speed sensor or tachogenerator labels for desired speed and flow rate 8 b If speed is too low, V tach is below both references; op-amp 1 saturates high and op-amp 2 saturates low. Transistor 1 is on, too slow warning lamp is on; transistor 2 is off, too fast warning lamp is off. If speed not too low or too high, V tach is between the two references; both op-amps saturate low. If speed is too high, V tach is above both references; op-amp 1 saturates low and op-amp 2 saturates high. Transistor 1 is off, too slow warning lamp is off; transistor 2 is on, too fast warning lamp is on. 5 1 mark for each of these five key points, however expressed. Page nine

33 Question Expected response 8 c 4 Max mark Additional guidance 1 mark for R 1 (answer and unit). 1 mark for substitution into formula. 1 mark for R 2 (answer and unit). 1 mark for R 3 (answer and unit). 9 a i Pulse Width Modulation 1 9 a ii 2 Square wave shown with the mark slightly bigger than the space. (1 mark) Axes labelled with voltage and time, and with appropriate values on time axis, to show correct proportion of mark and space. (1 mark) Page ten

34 Question Expected response Max mark Additional guidance 9 b i 8 V 1 1 mark for answer (with unit). 9 b ii 0 28 A 1 1 mark for answer (with unit). 9 b iii P = V x I = 8 x 0 28 = 2 2 W 2 1 mark for substitution into formula. 1 mark for answer (with unit). 9 c Larger velocity ratio than the alternatives. Takes up less space than a simple gear train. 9 d Good strength-to-weight ratio, due to shape. 2 Any two valid comparative points. No mark for simply stating, eg that a compound gear train allows a large velocity ratio; the response must involve a comparison to indicate it is the most appropriate choice. 2 Any two valid points. Will resist loading better, due to its higher tensile and compressive strength. Will resist corrosion well. Page eleven

35 9 e 9 1 mark for each of the three terms in the F v equation. 1 mark for answer (with units and direction) for R v 1 mark for each of the three terms in the F h equation. 1 mark for answer (with units and direction) for R h 1 mark for answer (with unit and direction) for R p Page twelve

36 10 a With the on/off valve on: 1. In the position shown, valve 1 can actuate the left-hand side of the group valve. 2. This switches off the air at the right side of the cylinder Z 5/2 valve. 3. This allows the left side to be actuated and cylinder Z to out-stroke. 4. When cylinder Z is fully out-stroked, valve 2 is actuated, out-stroking cylinder X. 5. When cylinder X is fully out-stroked, valve 4 is actuating the right side of the group valve and switching off the air to the left side of the cylinder X 5/2. 6. This allows the right side to be actuated, cylinder X then in-strokes. 7. When cylinder X is fully in-stroked, valve 3 is actuated and cylinder Z in-strokes. 8. If the on/off valve goes off, both cylinders return to their fully in-stroked position and the sequence stops. 8 1 mark for each valid step in description. 10 b i 1 pulse moves head 0 5 mm, so: 50 pulses are required per second to give 25 mms -1 each pulse + space = 20 ms ( 1 / 50 of a second) each space = 20 1 = 19 ms 2 1 mark for 20 ms or 50 pulses per second. 1 mark for answer: 19 ms Page thirteen

37 10 b ii 6 1 mark for each of: Startpos_x and return correctly expressed decision Step direction forward Both X steps (high and low) Two delays Loop back Page fourteen

38 10 c i Z Y X M marks for complete correct table. 2 marks for six or seven correct rows. 1 mark for four or five correct rows. 0 marks for three or less correct rows. 10 c ii Y 1 [END OF EXEMPLAR MARKING INSTRUCTIONS] Page fifteen