The Need Specification

References  Adapted from:  Design for Electrical and Computer Engineers, first edition, by Ralph M. Ford and Chris S. Coulston  Excerpts from the book “Engineering Design, a Project Based Introduction”, second edition by Clive I. Dym and Patrick Little. John Wiley and Sons, Inc. ISBN

What are Specifications?

 Specification A detailed and exact statement of particulars, a statement fully describing something to be built. American Heritage Dictionary  Specifications A detailed, exact statement of particulars, especially a statement prescribing materials, dimensions, and quality of work for something to be built, installed, or manufactured. answers.com  Specifications may indicate as well acceptance criteria (very important). Definitions

What to Specify?

6  The Objectives and The Problem Statement resulting from the attributes in the Need Analysis  Short statements that describe the need in the language of the client (or the user) like:  “The amplifier should have good sound quality” resulting from:  Interview, survey, brainstorming  Translate the Objectives into Engineering Language and attach numbers to them  The system should have Low Total Harmonic Distortion  Specification: THD < 1%  Constraining the Objectives What to Specify?

Translating the Need into Engineering Language and Technical Specifications Performance  Performance specifications identify performance levels that signify the achieved desired functional behavior.  The system should detect 90% of all human faces in an image.  The amplifier will have a total harmonic distortion less than 1%. 7

Who defines the specifications?

 The Client and the Team After the Need Analysis, requires One or more additional meetings

Objectives and Problem Statement Properties 1) Abstract: What the system will do, not how it will be implemented 2) Verifiable: There should be a way to measure or demonstrate that the objectives met in the final realization 3. Unambiguous: Each requirement should have a single unambiguous meaning and be stated with short complete sentences. 4. Traceable: Each Engineering requirement should be traceable to client, users or designers 10

Objectives and Problem Statement Properties  Good Example The robot must have move forward fast, with the ability to accelerate from standstill to the average speed in under one second.  Bad Example The robot uses IR sensors to sense its external environment and navigate autonomously controlled by a Raspberry Pi 11

Validation VS. Verification

Validation = Are we building the right product? (Objectives) Verification = Are we building the product correctly? (Specifications) 13 Validation

Technical specification  A complete list of the technical details for a given system, e.g., accuracy, speed, dimensions, etc  List as a table at the end of section

One Example

Marketing Requirements 1.The system should have excellent sound quality. 2.The system should have high output power. 3.The system should be easy to install. 4.The system should have low cost. Car Audio Amp

THD Output Power Marketing Requirements 1.The system should have excellent sound quality. 2.The system should have high output power. 3.The system should be easy to install. 4.The system should have low cost. Car Audio Amp Translate Marketing language into Engineering Language and find the technical specs and justifications

1, 2, 4The total harmonic distortion should be <0.1%. Based upon competitive benchmarking and existing amplifier technology. Class A, B, and AB amplifiers are able to obtain this level of THD. 1–4Should be able to sustain an output power that averages  35 watts with a peak value of  70 watts. This power range provides more than adequate sound throughout the automobile compartment. It is a sustainable output power for projected amplifier complexity. Marketing Requirements 1.The system should have excellent sound quality. 2.The system should have high output power. 3.The system should be easy to install. 4.The system should have low cost. Car Audio Amp

Probably most of user will not distinguish between.1% and.01% THD Or Probably 200 W will represent a hazard for users in a car Probably nobody will buy a 10% THD Or one that delivers a max of 5W

How to determine the values: Trade-Off THDPowerUsually the better the spec the more expensive to produce

How to determine the values: Trade-Off THD Power THD Power Usually the better the spec the more expensive to produce Probably improving the THD spec may require to impair a little the power spec to keep price reasonable

How to determine the values:  Competitive Benchmarks  Cost  Perception

Apex AudioMonster AmpsOur Design THD0.05%0.15%0.1% Power30W50W35W Efficiency70%30%40% Cost$250$120$ Competitive Benchmarks

Objectives Engineering RequirementsJustification 1, 2, 41.The total harmonic distortion should be <0.1%. Based upon competitive benchmarking and existing amplifier technology. Class A, B, and AB amplifiers are able to obtain this level of THD. 1–41.Should be able to sustain an output power that averages  35 watts with a peak value of  70 watts. This power range provides more than adequate sound throughout the automobile compartment. It is a sustainable output power for projected amplifier complexity. 2, 41.Should have an efficiency (  ) >40 %. Achievable with several different classes of power amplifiers. 31.Average installation time for the power and audio connections should not exceed 5 minutes. Past trials using standard audio and power jacks demonstrate that this is a reasonable installation time. 25 Car Audio Amp.

1–41.The dimensions should not exceed 6” x 8”x 3”. Fits under a typical car seat. Prior models and estimates show that all components should fit within this package size. 1–41.Production cost should not exceed $100. This is based upon competitive market analysis and previous system designs. Marketing Requirements 1.The system should have excellent sound quality. 2.The system should have high output power. 3.The system should be easy to install. 4.The system should have low cost. 26

Assumptions and Limitations  Assumption – The result of any project decision, which is required to complete the project definition, but is not a physical limit (minimum or maximum) that was imposed by the client, the technology used, or a physical law. Assumptions are the result of decisions that can be made by the team and affect the end- product design and implementation. Examples would include: The maximum number of simultaneous users of a computer program, or The maximum number of books to be stored on the shelves of a bookcase.  Limitation – The result of any project decision, which is required to complete the project definition, but is a physical limit (minimum or maximum) that was imposed by the technology used, or a physical law. Limitations are the result of things over which the team has no control, but must consider in its end- product design and implementation. Examples would include: The maximum weight or size of user that would fit in the product without damaging it. The maximum power consumption, or (Limited by size of PS or Breakers) The maximum speed of the end product (limited by the type of gates or microcontroller)

Assumptions and Limitations  We care about technical Assumptions and Limitations. Please do not list in your assumptions things like: The user has technical background or The weather will be fairly good  Do not confuse constraints with limitations

Operating environment  For any end product other than simply a calculation, it is essential to know the environment to which the end product will be exposed or experience.  For example, will the end product be exposed to dusty conditions, extreme temperatures, or rain or other weather elements?  Is the end product likely to be dropped or thrown?  This information is necessary in order to design an end product that can withstand the hazards to which it is expected to be exposed. This element shall be at least one paragraph in length.

Intended user(s) and intended use(s).  Knowing the characteristics of the end users makes it much easier to design an end product that will be accepted and used.  The expected end uses are equally important. This description should include what uses are expected as well as what uses are not to be considered

Specifications  THD < 0.1%.  Prms 35W  Ppeak 70 W  ƞ > 40 %  Average installation time < 5 minutes  Dimension 6” x 8”x 3”  Cost < $100  Input Voltage 12V (Operating Environment)  Temperature in Operation 0 < T < 50C (Operating Environment)  12 hour operation when car is off (limitation)  Human Interface: Touch Screen (Assumption)

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