GCE SYSTEMS AND CONTROL TECHNOLOGY

Transcription

1 GCE SYSTEMS AND CONTROL TECHNOLOGY SYST3 Report on the Examination 2555 JUNE 2015 Version: 1.0

2 Further copies of this Report are available from aqa.org.uk Copyright 2015 AQA and its licensors. All rights reserved. AQA retains the copyright on all its publications. However, registered schools/colleges for AQA are permitted to copy material from this booklet for their own internal use, with the following important exception: AQA cannot give permission to schools/colleges to photocopy any material that is acknowledged to a third party even for internal use within the centre.

3 Section 1 Question 1 This was a popular question and was answered by approximately half of the candidates. Part 01 The more able candidates considered all the energy requirements (not just electrical power) of the island and the variation of demand throughout a 24 hour period. Most candidates could give suitable methods and limitations of producing electrical energy from renewable and finite sources but often did not relate this to this situation. Part 02 The majority of answers clearly showed how the energy was harness and convert to an electrical form. The better responses took into account the variations of the input source and how the output could be regulated to ensure its suitability to charge a 12 volt battery. Question 2 This question was, answered by approximately 40% of the candidates. Part 03 A well answered question with most answers showing a clear understanding of three suitable systems. The majority of answers could discuss relative advantages and disadvantages and considered loading, speed, maintenance, reliability and energy loss. Candidates did not display the same depth of knowledge when suggesting specific applications for the systems. Part 04 Many candidates gave an explanation of anthropometric data and which data you would use when designing certain objects, but did not explain why you would use only 90% of data, therefore not having to consider the extremities at each end of the scale. Part 05 A well answered question with most candidates recognising that the average will only match a very small part of the population and would make the seating uncomfortable for the majority. Question 3 This question was the most popular and was answered by approximately two thirds of the candidates. 3of 6

4 Part 06 The majority of answers showed a good understanding of how conductivity and tensile strength are considered when selecting a material for a system or product. There was a lack of clarity when explaining hardness and toughness and where in a system or product is required for functionality. Part 07 The answers that achieved the higher marks considered electrical energy for a range of forms of transport, for example cars, bikes, buses, trains, trams and planes. This allowed them to consider a wider range of advantages and limitations than those who limited themselves to battery powered cars. Question 4 This question was answered by about 45% of the candidates. Part 08 A very well answered question with most candidates producing a clear well labelled circuit diagram with flowchart for a microcontroller based system linked to appropriate prime movers, both electrical and pneumatic. A number of solutions used a pneumatic control circuit for all but the buzzer circuit and there were a few elegant solutions based on mechanical control. The part that most candidates had problems with was controlling the speed of movement; they often referenced PWM but did not explain how it would be achieved. Part 09 A well answered question with the majority of candidates basing their answers around the temporary or permanent nature of the joint and the method of joining. They often were confused on which jointing process using heat could be used with which material. The better responses considered the product or system and the production methods. Question 5 This question and was answered by about a quarter of the candidates. Part 10 Candidates showed a good understanding of what was required and used both open and closed loop systems to achieve this. Open Loop These systems were normally based on a stepper motor. Candidates did not always consider the need for gearing to achieve the correct accuracy of movement. The method of producing the pulses for driving the stepper motor and how they related to the movement was also often omitted. Many candidates were confused on how a stepper motor is driven and used circuits more appropriate for a dc motor. 4of 6

5 Closed Loop The most common system consisted of a motor driving a speed reduction system and an encoder to provide feedback. The overall control was provided by a microcontroller. Many examples lacked the detail on how the required level of accuracy was achieved and how the encoder controlled the movement of the motor. The quality of the diagrams was generally of a high standard. Part 11 Most candidates attempting this question had a clear understanding of suitable sensors for measuring temperature and appropriate ways of connecting them to provide an output. The majority of responses used a sensor with an analogue output connected to an analogue input of a microcontroller. Unfortunately many candidates did not explain that it was the analogue input. The output system used was normally 7 segment displays with appropriate driver chips or LCD displays with serial inputs. Any form of display was acceptable but to achieve the higher marks it was necessary to explain how the input signal was converted to the correct form to drive the display. This also involved explaining what the correct form was. Question 6 This question was answered by about 40% of the candidates. Part 12 A reasonably well answered question with more able candidates clearly referencing the required level of accuracy. Most candidates used a fabrication system based around drawing the parts on CAD and the cutting them out using a laser cutter. The majority of answers clearly showed the size of the separate part although the explanation of how you would draw them and cut them often lacked detail. The better solutions to the joining of the parts normally included an aid or jig and clamping while joining. Very few candidates considered any form of finishing of the assembled object. Part 13 Most candidates suggested ether injection moulding or extruding and cutting to length. Both systems were acceptable as were a few others that were explained. In nearly all cases the answers gave a clear explanation of how the injection moulding or extruding process works, but they did not explain how the object could be manufactured because they made little or no reference to the mould or die and how that would be manufactured. 5of 6

6 Mark Ranges and Award of Grades Grade boundaries and cumulative percentage grades are available on the Results Statistics page of the AQA Website. Converting Marks into UMS marks Convert raw marks into Uniform Mark Scale (UMS) marks by using the link below. UMS conversion calculator 6of 6