Requirement Analysis

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Design for Electrical and Computer Engineers

3. Requirement analysis

Our plans miscarry because they have no aime. When a man does not know what harbour he is making for, no wind is the right wind

- Seneca, 4 BC to AD 65

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How will everyone with a stake know when it is done?

Important check point check point for the “go, no-go” decisions that are a part of the design process from beginning to end

3. Requirement analysis

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3.1 The importance of the requirement specification

Costs accumulate exponentially as the design proceeds

Fewer than one in ten design projects results in a commercially viable product

Identifying a design that should not be pursued, and doing so early in the design cycle will make a positive contribution to the company’s bottom line

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Methodological approach: Requirement Analysis

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3.2 Developing the requirements specification

In this requirement analysis stage,

The focus is on a customer who needs a solution to a problem

In this step, engineer’s concern is not

- to solve problem

- but rather to understand what the problem is.

Engineering Goal is

- to clarify, define, quantify the design objectives

- to state these in the requirement specification.

Customers can

- take different forms: client or marketing department

- informed customer, frontier customer

Design engineer should be prepared to act as a coach, mentor, expert, careful listener and adviser

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Probability of proceeding to next stage design

Relative high Relatively low

Informed customer Frontier customer

Customer’s knowledge

High - customer knows and understands what the design accomplish

Low – No appropriate experience or example

Availability of information

- Customer- Equipment supplier- Competitor- Book, Journal

- No existing equipment- No similar design

Requirements specification

Relative easy Relative difficult

3.2 Informed and Frontier customer

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3.2.1 Bell Lab’s Example

Bell Labs engineers are assigned the task of a new telecommunication equipment with low back-ground noise

What is the maximum allowable level of back ground electronic noise on the telephone circuit?

Customer’s needs

How will I know when I am done?

Design criteria needed

Very subjective

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dBrnc represents an audio level measurement, typically in a telephone circuit, relative to the level of circuit noise,

• They conducted several years effort on noise measurement • The result is a characterization of noise in terms of power and frequency

noise

signal

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3.2.2 Two stage approach for requirement specification

Output of this process is a document!!! - What exactly is the design team to do? - How will everyone know when the design is done?

First stage Assess the need of the customer Organize the input into a statement of the design problem

Second stage Refine the problem statement by adding additional detail (a technical and quantified specification)

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3.2.3 Real world consideration

Real world inputs to the Design Process

How?

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3. 3 Needs assessment – stating the problem

Nontechnical- Problem should be state in language of customer

Specifiable- Although the problem statement is subjective, it should align with the more

detailed and quantitative requirements specification

Non-quantifiable- No specific dimension, quantities, and cost

Complete- The problem statement should cover all aspect that engineer anticipate

during the design

First opportunity to understand the requirement of design

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To define the design problem

What is the problem to be solved? Why is there a problem? What is my role in solving the

problem? How will I know when I am done?

Budget and schedule constraints

When is the solution needed? What is the upper limit of cost?What are your expectation of production cost, in high volume

Reliability and maintenance

What are the consequences of the system failing once in operation?

What resource are available for maintenance?

Question of contract

How will it be determined when the design is completed?

How will it be determined that the design is acceptable?

How will I be paid? Is the work that I am to do legal?

Engineer have to take initiativein questioning the customer on the needs

3. 3.1 Question the Customer

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3.3.2 Needs and Wants

If the problem statement was developed to reflect wants instead of needs

We needs more feature than our competitor's product and must be cheaper to produce

Which features needed?How much cheaper?

- Unneeded features would be provided resulting in extra cost

- Some needs would not be met, resulting in design deficiencies

Engineer’s job is to translate the customer’s wants into a problem statement that reflects true needs

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3.3.3 Explore Project Boundaries

External factor limit alternative solutions that engineer can consider when doing a design

There are legal boundaries to contend with

Project boundary are imposed by the need to fit within existing operations, standard, method, or procedure.

ex) the customer need a common operating system and hardware platform so as to minimize staff training needs and simply maintenance

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3.3.4 Input/output Analysis

Input/output diagrams useful for finding unforeseen needs and indentifying for functions

hidden inputhidden output

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3.3.5 Preview the User Interface

Most electronic products or systems exchange information with a human user. This exchange takes place through an interface that can take many forms

– A keyboard, a switch, an audible tone, a visual indicator, a computer screen

The requirement statement must include the definition of user interface

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3.3.6 Survey Design Attributes

Nonfunctional Attributes

User Interface

Packaging

Battery

Production

Reliability

Functional Attributes

Standard Functions

Advanced Functions

• There are a number of attributes that are common to most design.• Surveying them and assessing their relevance to the design problem will help expose needs

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3.3.7 Conflicting Needs

Don’t resolve the solution, which force customer to be realistic and to recognize need that may not be necessary

Conflicting design needsCorrelation Matrix

clarify possible design conflicts

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3.3.8 Draft of Operational Manual

A. Product Overview

B. Installation1. Flow sensors2. Velocity sensors3. Cabling4. Cutoff5. Control unit

C. Initial Setup1. Alignment of sensors2. Calibration3. Testing

D. Operation1. Metric and imperial units of measure2. Monitoring application rate and implement velocity3. Cumulative measure – spray, area, distance4. Alarms5. Calibration check

E. Maintenance 1. Routine servicing2. Trouble shooting

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The amount of background noise heard on the telephone should not annoy the users

Idle channel noise must be less than or equal to the 23 dBrnc

Translate the needs to specification quantitatively in technical terms

3.4 Preparing the requirement specification

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Translation method

1. Search out expert source

2. Analyze similar designs

3. Conduct test or experiments

3.4.1 Translating Needs to Specification

Requirement specification

1:1 translationDesignneeds complete, consistency

*Completeness : all design needs are covered *Consistency : there are no contradictions among the different design

needs

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User interface must be thoroughly specified in the requirement specification

3.4.2 Specification of Interface Points

<Example>

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3.4.3 Excessive Requirements

Relationship between cost of design and product feature

Cost-Reliability trade-off

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3.4.4 Verification

If a design cannot be verified it should not specified

Unverifiable parameter must be removed or restated in a form that can be verified

It will be necessary to verify whether or not a design fulfills the needs of the customer as stated in the requirements specification.

Final test

Test planre

fine

d

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3.4.5 Document of requirement specification

1. Overviews

2. Statement of the problem

3. Operation description (draft user’s manual)

4. Requirement specification

5. Design deliverables

6. Preliminary system test plan

7. Implementation considerations

- service and maintenance

- manufacture

Attachments - A. Study (lab reports or marketing studies, for example) - B. Relevant codes and standards

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SUMMARY

It should be the engineer’s contribution to manufacturers, operators, maintainers, and future designers – a reference document to help them in their work

Requirement Specification

It should be an agreement between the engineer and the end user of the design

It should be the engineer’s guide as he or she moves through the design process

It should be the yardstick by which the completed design will be judged for its conformance to the initial objectives

It should provides a historical record of how the idea for the design came to be