-SQA-SCOTTISH QUALIFICATIONS AUTHORITY HIGHER NATIONAL UNIT SPECIFICATION GENERAL INFORMATION

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1 -SQA-SCOTTISH QUALIFICATIONS AUTHORITY HIGHER NATIONAL UNIT SPECIFICATION GENERAL INFORMATION -Unit Number Superclass- -Title- XJ BRUSHLESS DC AND STEPPER MOTORS DESCRIPTION- GENERAL COMPETENCE FOR UNIT: Evaluating the operating performance of brushless dc and stepper motors. OUTCOMES 1. evaluate the performance of brushless dc motors; 2. evaluate the performance of stepper motors; CREDIT VALUE: 0.5 HN Credit ACCESS STATEMENT: Access to this unit is at the discretion of the centre. However, it would be beneficial if the candidate had prior knowledge of basic Electrical Motor Theory and Practice. This may be evidenced by the possession of NC module: Electrical Machine Principles Electrical Motor Applications or similar qualifications or experience For further information contact: Committee and Administration Unit, SQA, Hanover House, 24 Douglas Street, Glasgow G2 7NQ. Additional copies of this unit may be purchased from SQA (Sales and Despatch section). At the time of publication, the cost is 1.50 (minimum order 5.00).

2 HIGHER NATIONAL UNIT SPECIFICATION STATEMENT OF STANDARDS UNIT NUMBER: UNIT TITLE: BRUSHLESS DC AND STEPPER MOTORS Acceptable performance in this unit will be the satisfactory achievement of the standards set out in this part of the specification. All sections of the statement of standards are mandatory and cannot be altered without reference to SQA. OUTCOME 1. EVALUATE THE PERFORMANCE OF BRUSHLESS DC MOTORS PERFORMANCE CRITERIA (a) (b) (c) (d) (e) Explanation of the constructional features of a brushless dc motor is clear and concise. Explanation of the operation of a brushless dc motor is correct. Evaluation of the operating features of a brushless dc motor is correct. Explanation of the applications of brushless dc motors is clear and concise. Explanation of the facilities available with integrated circuit brushless dc motor speed control is correct. RANGE STATEMENT Operating Features: life of motor; reliability; maintenance requirements; radio interference; efficiency; motor torque; motor speed; cost of motor. Facilities: motor operation; braking; overcurrent protection; speed regulation; timing. EVIDENCE REQUIREMENTS Written/graphical and/or oral evidence of the candidate s ability to explain the constructional features, operation, operating features and applications of brushless dc motors, and explain the main facilities of integrated speed control circuitry associated with brushless dc motors as detailed in pc (a) to (e). 2

3 OUTCOME 2. EVALUATE THE PERFORMANCE OF STEPPER MOTORS PERFORMANCE CRITERIA (a) (b) (c) (d) (e) Outline of the constructional features of the two main types of stepper motors is clear and concise. Evaluation of the operating parameters of stepper motors is correct. Explanation of the principal methods of damping in stepper motors is clear and concise. Description of a stepper motor s principal modes of operation are correct. Explanation of methods of adjustment of the main operating features within an integrated circuit stepper motor speed controllers is correct. RANGE STATEMENT Two main types of stepper motor: permanent magnet; variable reluctance. Operating parameters: step response; stepping rate; step angle; step angle accuracy; overshoot; settling time. Damping methods: slip clutch; viscous; resistive; capacitive; two phase. Principal modes of operation: rest mode; stall mode; bi-directional; slewing. Main operating features: supply voltage range; load current maximum; stepping rate; direction of rotation; noise immunity; prevention against transient power supply spikes. EVIDENCE REQUIREMENTS Written/graphical and/or oral evidence of the candidate s ability to explain the constructional features, operating parameters and damping methods in stepper motors, describe a stepper motor s principal modes of operation and explain the main facilities of integrated speed control circuitry associated with stepper motors. MERIT A candidate who achieves all performance criteria for all outcomes will be awarded a pass in the unit. Pass with Merit may be awarded to a candidate who achieves all outcomes and in doing so consistently demonstrates superior performance when for example: explaining the constructional features and operation of motor types (eg a greater depth of knowledge or more penetrating grasp of concepts); 3

4 (iii) transferring knowledge and understanding to more complex applications of dc motors; evaluating the operating characteristics of dc motors (eg a greater awareness of the significance of the parameters when applied to various load conditions). ASSESSMENT In order to achieve this unit, candidates are required to present sufficient evidence that they have met all the performance criteria for each outcome within the range specified. Details of these requirements are given for each outcome. The assessment instruments used should follow the general guidance offered by the SQA assessment model and an integrative approach to assessment is encouraged. (See references at the end of support notes). Accurate records should be made of the assessment instruments used showing how evidence is generated for each outcome and giving marking schemes and/or checklists, etc. Records of candidates achievements should be kept. These records will be available for external verification. SPECIAL NEEDS Proposals to modify outcomes, range statements or agreed assessment arrangements should be discussed in the first place with the external verifier. Copyright SQA 1997 Please note that this publication may be reproduced in whole or in part for educational purposes provided that: no profit is derived from the reproduction; if reproduced in part, the source is acknowledged. 4

5 HIGHER NATIONAL UNIT SPECIFICATION SUPPORT NOTES UNIT NUMBER: UNIT TITLE: BRUSHLESS DC AND STEPPER MOTORS SUPPORT NOTES: This part of the unit specification is offered as guidance. None of the sections of the support notes is mandatory. NOTIONAL DESIGN LENGTH: SQA allocates a notional design length to a unit on the basis of time estimated for achievement of the stated standards by a candidate whose starting point is as described in the access statement. The notional design length for this unit is 20 hours. The use of notional design length for programme design and timetabling is advisory only. PURPOSE This unit will allow candidates to develop an ability to evaluate the performance of brushless d.c. and stepper motors so that they have a better understanding of their use in industrial applications. This unit would be suitable as a component of a Higher National course of study. CONTENT/CONTEXT The following information gives further clarification regarding the context in which outcomes and performance criteria could be achieved. It is recommended that candidates are given the opportunity to examine the various parts of motors so that they can relate more clearly to information given about the construction of the motor types. Outcome 1 With reference to the application of brushless d.c. motors in performance criterion (d) emphasis should be placed upon the high speed application of these motors (eg top speed of 30,000 r.p.m. with some manufacturers claiming 100,000 r.p.m.). Applications should also be related to the high reliability and low maintenance of brushless d.c. motors. Typical applications might include the following: (iii) (iv) (v) (vi) cryogenic coolers; artificial heart pump motors; gyroscopic motor; tape drives for video recorders; tape transport systems; stereo record turntables. 5

6 Outcome 2 Use of graphs to illustrate some of the key characteristics of stepper motor operation would help to enhance the candidate s understanding of the subject. For example, graphs showing stepper motor stepping behaviour (including settling time) and stepper motor overshoot would aid understanding. APPROACHES TO GENERATING EVIDENCE During the work of the unit candidates should have a number of opportunities to develop problem solving and communication skills. Each candidate should be assessed at appropriate points throughout the unit. Where a candidate is unsuccessful in achieving an outcome, provision should be made for remediation followed by re-assessment. ASSESSMENT PROCEDURES In order to achieve this unit, it is suggested that the candidate attempts at appropriate times, two summative assessments in a formal context and must present sufficient evidence that they have met all performance criteria for each outcome, as specified within the criteria for each outcome. Examples of Instruments of Assessment which could be used are as follows but should not be taken as mandatory. Outcome 1 and 2 It is suggested that both outcomes be assessed by means of an assignment report (of the order of 2500 words plus diagrams per report). Assessors should ensure that the assignment is so structured that the candidate has the opportunity to cover all the performance criterion in each of the outcomes. PROGRESSION It is recommended that this unit be offered in the following HNC/D awards; HNC/D Engineering: Electrical; HNC/D Engineering: Electronics; HNC/D Engineering: Computer Technology, HND Engineering: Service Engineering and HNC/D Engineering. This unit is of a specialist nature and has no natural progression route. REFERENCES 1. Guide to unit writing. 2. For a fuller discussion on assessment issues, please refer to SQA s Guide to Assessment. 3. Information for centres on SQA s operating procedures is contained in SQA s Guide to Procedures. 4. For details of other SQA publications, please consult SQA s publications list. 6

7 Copyright SQA 1997 Please note that this publication may be reproduced in whole or in part for educational purposes provided that: no profit is derived from the reproduction; if reproduced in part, the source is acknowledged. 7