PM-1 Course : The Performance Specifications



Definition of The performance specifications: see fig.1

A performance specification defines the requested performance & the functional requirements for the product, the intended use, service environmental conditions, maintainability, and necessary interface and interchangeability characteristics. 



fig(1) performance specifications for a Robot Arm


Why We Need Performance Specifications?


In general, specifications communicate the user's requirements to the manufacturer. It tells the manufacturer:

1) What we will consider an acceptable product, and
2) how we will determine if the product is acceptable.

To the extent that any specification does these two things, it is good. The problem arises when we use specifications to tell the manufacturer how to make the product and we are not absolutely sure how to make it, or we communicate our knowledge poorly, or we truly need improved products.

Hence, Performance specifications leave out unnecessary "how to" or detail and give the manufacturer latitude to determine how to best meet our stated needs. The word "unnecessary" is emphasized because some detail requirements are necessary in a performance specification.

examples of performance requirements:

Examples of Performance Requirements
Reason
The circuit breaker shall not trip when subjected to the class 1, type A, shock test specified in MIL-S-901.
States required results.
The detector shall not contain foreign matter -- such as dust, dirt, fingerprints, or moisture -- that can be detected by visual examination.
Provides criteria for verifying compliance. (Assuming that foreign matter affects detector performance)
The shoes shall be of the following standard men's sizes: 9, 9-1/2, 10, 10-1/2, 11, 11-1/2, 12, 12-1/2, 13
Provides interface requirement.
The equipment shall withstand, without damage, temperatures ranging from -46 C° to +71 C°.
Defines operational environment.



Examples of Unnecessary Detail
Reason
The cloth shall be made from cotton that has been carded and spun into single yarn for both the warp and filling. The weave shall be a 5-harness sateen. The filling effect side shall be finished and identified as the "face" side.
This tells the manufacturer how to make the cloth, not what type and quality of cloth the user desires.


performance specification Characteristics :


In general, performance requirements should have the following characteristics:

1- Requirements should be quantitative rather than qualitative. Owner/consultant requirements that are not based on quantitative data are extremely sensitive to varying interpretations and misunderstanding.

Example
Overall length of the tractor shall be 150 inches or less.

2- Requirements should be verifiable. The Owner/consultant must be able to determine through analysis, test or demonstration if a product will perform as required.

Example
The mandrel shall have a hardness of not less than 60 and not more than 65 on the Rockwell "C" scale.

3- Performance requirements should describe interfaces in sufficient detail to allow interchangeability with parts of different design. Interface considerations should be addressed carefully when using performance specifications. For example, the specification must enumerate the interface requirements necessary to allow maintenance at the appropriate level, but it must not impose a design solution beyond that necessary to ensure a proper interface.

Example
Provision shall be made for installation mounting of the Position and Azimuth Determining System, with a control and display unit in the Type A utility truck.
Provision shall be made for installation of 24 volt DC power cable access to the equipment.
The size of the PADS unit is approximately 26x31x20 inches.
The weight of the unit is 317 pounds.

4- Requirements should be material and process independent. It should be possible to change material and processes without changing the performance specifications.

Example
All mowers shall be treated with the manufacturer's commercial standard rust-proofing treatment.
Not: All mowers shall be rust-proofed in accordance with MIL-SPEC-xxxx.



to download a copy of a Template for performance Specifications, please click Here

in the next topic, I will explain the technical design specifications.

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