What are Engineering Specifications?

Specifications are quantitative, measurable criteria that the product is designed to satisfy.   In order to be measurable and unambiguous, specifications must contain a metric, target value and engineering units for the target value.

Metric – The metric is the characteristic of the product that will be measured. For example,  an automobile design team might measure the distance of the car as the car decelerates from 60 miles per hour to a complete stop.

 Engineering Units- A unit of measurement is a definite amount of a physical quantity  defined and adopted by convention and or law, that is used as a standard for measurement of the same physical quantity of any amount.  Examples of engineering units are seconds, degrees Celsius, Kilograms, Newtons etc.  For example, the metric of braking distance may be measured in units of meters.

 Target Value – Target values is the range of the metric that is acceptable,  Examples of target values include “less than 6 seconds”,  “greater than 7 pounds” or “between 20 and 50 Kilograms”.  For the braking distance example, the range of acceptable values might be less than 30 meters.

Example of a Specification

Specification: The car will brake from 60 miles per hour to a complete stop in less than 30 meters.

Metric: Braking distance of the car as the car decelerated from 60 miles per hour

Units: Meters

Target Value: Less than 30 meters

Why do we need Specifications?

Specifications are the performance goals for the design team.  During the design process, the analytical and physical prototypes are tested against the specifications.  A design is not complete until a full prototype has been tested and all specifications have been satisfied.   You will learn to use the house of quality methodology to translate interpreted needs into specifications