Writing a Product Design Specification or PDS can be a difficult task, but a necessary one in order help collate information from the Planning and Clarification Stage.
All major corporations have a PDS for their products. A PDS helps to limit the range of acceptable solutions (Cross 2009: 105) and compiles the Brief (and subsequent processes) into a technical framework providing additional clarification (Haik and Shahin 2011: 153). The concepts and attributes of the product being specified, together with any constraints , need to be set out to the appropriate degree of detail (BS7373-1 2001: 1). It is different from the Scope, the PDS combines the information from all steps within the Planning and Clarification stage. Figure 1 shows how each area interacts and what specific information is collated into the PDS.
Figure 1 – Inputs from Planning and Clarifiation stage into PDS.
A PDS is compiled in accordance to BS 7373-1:2001. This British Standard ensures that the manner in which the information is ordered and described should follow a similar pattern (BS7373-1 2001: 5) , thus reducing the possibility for error and misunderstanding. BS7373 is accessible, thus;
You must be on campus using University’s connection.
Type ‘elib.coventry.ac.uk’ to access elibrary
Type ‘British Standards’ into the search field.
Click ‘British Standards Online’.
Search for ‘BS7373-1:2001’ .
A PDS is a basic control document and reference document for the design and manufacture of the product (Dieter and Schmidt 2009: 109). However it may evolve and change over the course of the project, hence the review after each stage. As more information is discovered or developed at each stage, the document will change and update to accommodate the differences such that by the end of the project, the PDS will describe in writing the product to be manufactured and marketed (Dieter and Schmidt 2009: 111). The level of detail in a specification usually depends on its intended use. The end product usually has an inherent unwritten specification that is implied by industry standards and common practice (BS7373-1 2001: 4).
It should avoid forcing the direction of the design and being purposefully sabotaged in an attempt to guide the concept selection process, thus prescribing the outcome. It should be as complete as possible before the Concept design process begins, however as mentioned it is a dynamic document that is likely to change at the time periods specified on the model. Written correctly, it will remove the need to constantly check the QFD and Brief to ensure you’re still on track. Although, you should keep a note of these; when the project is finished you will need to reflect on the differences (if any) in your Conclusions and Recommendations section of your report.
You should only present the FINAL version of your PDS within your report. Previous revisions should be added to an Appendix and made reference to throughout the Report. The PDS should be presented as it’s own chapter and should be in accordance to BS7373.
It should contain metric information, always labelled with units (SI preferably). It culminates the interpretations of the vague statements derived from the brief that have been transformed in previous stages into numerics (Think; QFD – Customer Requirements and how they’re changed into Engineering Characeristics). For example “low weight”, could be anything from 10kg to 500kg, depending on the application; this number will have been clarified in the Understanding the Brief and QFD steps.
Example PDSs can be viewed under the follwing Links.
Product Design Specification – Portable Winch – Compiled for a 1st year lecture. Good complete example.
Many PDSs for a variety of projects – Compiled from previous student projects, some more complete than others.
Locate and download BS7373 using the instructions above. Store it locally on your home computer. Download the example of the Portable Winch above. Store it locally on your computer. READ IT. Table 1 is taken from the BS7373 document and defines the structure of a PDS. Below is a description of the sort of material required for each entry. For a more detailed description of each area, access the document yourself following the instructions in bold, above.
| Item | Content |
| Identification | Title, references number, authority, designation, issue number and date. |
| Circulation | Distribution list of specification. |
| Contents | List of parts, clause, illustrations and annexes. |
| Foreword | Reasons for writing the specification. |
| Introduction | Summary of contents and technical aspects of objectives. |
| Scope | Range of objectives/content. |
| References | Statement of policy regarding documents. |
| Definitions | Terms used with special meanings in the text. |
| Main body of the specification | Requirement, guidance and methods. |
| Annexes | Additional detailed technical information and examples. |
| Index | Alphabeticcal index. |
| Bibliography | Details of internal and external standards and publications referred to in the specification. |
Table 1 – Checklist of main items (BS7373-1 2001: 6).
The ‘Main body of Specification’ or requirements section, could sub-list any or all of the following areas. A more detailed list of possible inclusions can be found in BS7373, so locate it now. What are you waiting for?
| Area for Body | Description |
| Size | Both of individual components and overall limitations to size. Is there either a maximum or minimum size? See also Ergonomics. |
| Economics | Is there an upper cost limit or target price for the article? |
| Time | Is there a timescale involved? |
| Strength | How strong does the completed item have to be? |
| Durability | How long will the item need to last? What forces/wear and tear will the item be subjected to? |
| Reliability | Will the article function consistently and correctly? |
| Maintenance | Will regular maintenance be required? If so are the parts easily accessible? |
| Material | Do any particular materials need to be used and what materials are available? Can any materials not be used? |
| Weight | Are there any limitations to the weight of the finished article? |
| Surface Finish | What degree of protection and appearance is required? |
| Shape/Form | Does the design have to follow a particular style? |
| Environment | Where will the completed article be situated? Does it need to match its surroundings? |
| Aesthetics | Is its appearance important? |
| Ergonomics | Is the article going to be used directly by people? If so will they be able to use it easily and comfortably? |
| Safety | Does the item have any potential hazards? Will its failure be liable to cause injury? |
| Standards | Does the design have to conform to any British Standards? |
| Quantity | How many of the items will be made? |
Table 2 – Main body of Specifcation, sub-elements.
For more inforamtion on PDS writing consult any book in the area of Engineering Design, the majority will have a section on PDS writing. This page has been compiled using these books;
Haik and Shahin – Engineering Design Process – Chapter 6.
Dieter and Schmidt – Engineering Design – Chapter 5.
Cross – Engineering Design Methods – Chapter 8.
Specification Writing – BS 7373-1: 2001.
Lecture Notes from 103MAE.
Back to Planning and Clarification
Back to MAE Design Model