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 0471-25687-0

What are Specifications?
Definitions

Specification A detailed and exact statement of
particulars, a statement fully describing
something to be built.


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.


American Heritage Dictionary
answers.com
Specifications may indicate as well acceptance
criteria (very important).
What to Specify?
Definitions


Marketing Requirements (Statements of the
Client and User Needs)
In your case The Marketing Requirements are
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)
“The amplifier should have good sound quality”
Interview, survey, brainstorming
6
Definitions

Engineering Requirements
Short statements that describe the technical
needs of the design
 The Marketing Requirements should be
translated into Engineering Requirements
 “The amplifier should have low harmonic
distortion”


In your case The Specifications will be
derived from the Engineering
Requirements, In other words, you need
to find specifications for the objectives.
7
Who defines the
specifications?
Who defines the specifications?
The Client and the Team.
 After the Need Analysis
 One or more meetings

Marketing and Engineering
Requirements, where do they fit
in the Proposal?
10
Marketing and Engineering
Requirements

Marketing Requirements: In the Problem
Statement and Need Analysis sections the
results from the interview, survey and
brainstorming will show the Marketing
Requirements
 Engineering Requirements: In the End
Product Description and Specifications
section of your proposal you translate the
Marketing Requirements into Engineering
Requirements.
Engineering Requirements
Properties
Abstract
1)

What the system will do, not how it will be
implemented
Verifiable
2)

There should be a way to measure or
demonstrate that the requirement is met in
the final realization
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Engineering Requirements
Properties
Unambiguous
3.

Each requirement should have a single
unambiguous meaning and be stated with
short complete sentences.
Traceable
4.

Each Engineering requirement should be
traceable to a Marketing Requirement
IEEE Std. 1233-1998
13
Example
Does the following requirement meet the
four desirable properties? (abstract,
verifiable, unambiguous, traceable)
“The robot must have an average forward
speed of 0.5 feet/sec, a top speed of at
least one foot/sec, and the ability to
accelerate from standstill to the average
speed in under one second.”
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Example
Does the following requirement meet the
four desirable properties? (abstract,
unambiguous, verifiable, traceable)
“The robot must employ IR sensors to sense
its external environment and navigate
autonomously with a battery life of one
hour.”
15
Identifying Engineering
Requirements

In addition to Interviews, surveys and
brainstorming




Observation of processes and devices in use
Benchmarking and market analysis
Prototyping and simulation
Research survey
16
The Requirements Specification
17
Requirements Specification
Collection of both Marketing and
Engineering requirements that the design
must satisfy in order for it to be
successful.
 The Requirements Specification organizes
and communicates requirements to:



The client and the technical community (two
different languages).
Your Requirements Specification is: The
whole Proposal
Requirements Specification
Properties of the Requirements
Specification

Normalized/Orthogonal


No redundancy between engineering
requirements
Complete Set

Addresses all of the needs



Client
User
Designer
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Properties of the System
Requirements Specification

Consistent


Bounded


No contradictions among the requirements
Minimum bound for acceptable target
(Technical specifications, numbers)
IEEE Std. 1233-1998
21
Validation VS.
Verification
Validation
Validation = Are we building the right
product? (Marketing Requirements)
Verification = Are we building the product
correctly? (Technical Specifications)
23
Technical specification

A complete list of the technical details for
a given system, e.g., accuracy, speed,
dimensions, etc


Attaching numbers to the Engineering
Requirements
List as a table at the end of section
The Process
25
Translating the Need into Engineering
Requirements and Technical Specifications
Express your objectives in Engineering
Language (Engineering Requirements)
 Find the Engineering Requirements
Technical Specifications (Specs)


There are different ways to do it
Translating the Need into Engineering
Requirements 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%.

27
Translating the Need into Engineering
Requirements and Technical Specifications

Procedural specifications identify specific
procedures for calculating attributes or
behavior. For example:

The design is safe if its maximum current at
the input, when the output is shorted is less
than 5A.
Translating the Need into Engineering
Requirements and Technical Specifications
Reliability & Availability
 The system will have a reliability of 95%
in five years.
 The system will be operational from 4AM
to 10PM, 365 days a year.
Translating the Need into Engineering
Requirements and Technical Specifications
Energy
 The system will operate for a minimum of
three hours without needing to recharge
Operating Environment
 The system should be able to operate in
the temperature range of 0°C to 75°C.
 The system must be waterproof and
operate while submersed in water.
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One Example
Car Audio Amp
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.
Translate Marketing language into Engineering Language and find the
technical specs and justifications
Car Audio Amp
1, 2, 4
1–4
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.
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.
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.
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
THD
Power
Usually the better the spec the
more expensive to produce
How to determine the values:
Trade-Off
Power
Probably improving the THD spec
may require to impair a little the
power spec to keep price
reasonable
THD
THD
Power
Usually the better the spec the
more expensive to produce
How to determine the values:
Competitive Benchmarks
 Cost
 Perception

Competitive Benchmarks
40
Apex Audio
Monster Amps
Our Design
THD
0.05%
0.15%
0.1%
Power
30W
50W
35W
Efficiency
70%
30%
40%
Cost
$250
$120
$100
Car Audio Amp. Your Specs should
look like this
Marketing
Requirement
Engineering Requirements
s
1, 2, 4
1. The total harmonic distortion
should be <0.1%.
Justification
Based
upon
competitive
benchmarking
and
existing
amplifier technology. Class A, B,
and AB amplifiers are able to obtain
this level of THD.
This power range provides more
than adequate sound throughout
the automobile compartment. It is a
sustainable output power for
projected amplifier complexity.
1–4
1. Should be able to sustain an
output power that averages 
35 watts with a peak value
of  70 watts.
2, 4
1. Should have an efficiency ()
>40 %.
Achievable with several different
classes of power amplifiers.
1. 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.
3
41
1–4
1. 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.
1–4
1. Production cost should not This is based upon competitive
exceed $100.
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.
42
Advanced Requirements Analysis
43
1) Sound Quality
+
2) High Power
+
3) Install Ease
+
4) Cost
-
+
+
-
-
Cost
Dimensions
Install Time
, Efficiency
Output Power
THD
Engineering Marketing Matrix
-
Used to determine the impact of Marketing requirements
over Engineering Requirements
44
THD
Output Power
, Efficiency
Install Time
Dimensions
Cost
THD
Output Power
, Efficiency
Install Time
Dimensions
Cost
Engineering Tradeoff Matrix
-
+
+
-
-
-
+
+
-
Used to determine the impact of Engineering requirements
over other Engineering Requirements
46
Engineering Tradeoff Matrix
Competitive Benchmarks
48
Apex Audio
Monster Amps
Our Design
THD
0.05%
0.15%
0.1%
Power
30W
50W
35W
Efficiency
70%
30%
40%
Cost
$250
$120
$100
The House of Quality
When looking at Peak
Closing Force, we see
that improving this will
impair the Door Seal
Resistance
The House of Quality
The House of Quality
Review
Properties of engineering requirements
 Examples of engineering requirements
 Properties of the System Requirements
Specification
 Advanced Requirements Analysis



Tradeoff matrices
Benchmarks
53
&
Questions
Answers