Specifications Guidelines

Product Specification Terminology

We begin by providing a basis for a common understanding of the language used at Keysight Technologies when discussing product specifications. Figure 1 depicts the hierarchy of terms. Product information is an overall term for any attribute used to describe a product and its capabilities. It is the most general term used for discussing the property of a product.

A feature is an attribute of product offered as a special attraction. Features describe, or enhance, the usefulness of the product to the customer. A feature is not necessarily measur­able; however, it may have an associated measurable parameter. If a feature with a measurable parameter is of interest to the customer, a product specification describes its performance. For example, HP-IB I/O interface is a feature and it is not measurable but Narrow Resolution Bandwidth Filter is a feature with the measurable parameter bandwidth.

Specifications formally describe product performance. A specification is a numerical value, or range of values, that bounds the performance of a product parameter. The product warranty covers the performance of parameters described by specifications. Products meet all specifi­cations when shipped from the factory, or from an Keysight Customer Service Center following calibration.

Environmental specifications bound the external conditions applied to a product for which the specifications are valid. Some specifications are only valid over a limited, or restricted, set of external conditions but in such cases the specification includes a description of these limited conditions. The environmental specifications also define the conditions that a product may be subjected to without permanently affecting product performance or causing physical damage. These can be climatic, electromagnetic (as related to electromagnetic susceptibility), mechani­cal, electrical (as related to the power requirements of a product), or preconditions of operation (e.g., warm-up time or calibration interval).

Characteristics describe product performance that is useful in the application of the product, but is not covered by the product warranty. They describe performance that is typical of the majority of a given product, but is not subject to the same rigor associated with specifications.

Characteristics are often referred to as Supplemental Characteristics, Typical or Nominal values but these terms are not formally defined. However, supplemental characteristic is a generic term generally referring to all non-warranted product performance. The terms typical and nominal generally indicate the expected performance of a given product.

Specifications

Specifications describe the performance of parameters covered by the product warranty. The specifications do not, however, imply that any specific statistical distribution describes the performance of a parameter. Rather, the specifications simply bound the quantity of a parameter. This section outlines the model used to verify that products meet the specifications. The model was presented by Sherry Read and Timothy Read in the Hewlett-Packard Journal of June 1988, in their article “Statistical Issues in Setting Product Specifications”.

Figure 2 depicts the statistical model for the specifications. The model represents the relation­ship of a measured parameter and the specification. It shows a single-sided specification but a generalization of the model represents two-sided specifications that bound both sides of a parameter. Each element of the model is described.

Guardband is the difference between the test line limit and the value of the specification. The guardband accounts for measurement uncertainties, changes in performance due to external conditions, drift and any other mechanism that may affect performance. The application of guardband ensures, with a high level of confidence, that a product measured and found to be within the test line limit will meet the specification.

The test line limit is the pass-or-fail limit used by the manufacturing test procedures. The manufacturing test procedures perform measurements on products but not all parameters are actually measured. The performance parameter may be inferred through statistical correlation, sample testing, or other sound means. Products found to be outside the test line limit undergo repair and re-test.

The performance distribution represents the unit to unit variation of a parameter measured by a manufacturing test procedure. Production margin is a measure of the producability of the product. The proximity of the test line limit to the performance distribution determines the size of the production margin. A small production margin results in low yields from the manufactur­ing test procedures. A larger production margin results in higher yields but a potentially less competitive specification.

Delta environmental represents the possible change in performance of a product over the range of external conditions applied to a product. Typically, the manufacturing test procedures execute under a limited set of external conditions; usually this is room temperature (25 ºC), 10 to 90% relative humidity and insignificant levels of electromagnetic interference, mechanical vibration and shock. Delta environmental guardband ensures that a product tested under a limited set of conditions meets the specifications for all conditions described by the environ­mental specifications.

Drift represents the possible change in performance of a characteristic over the calibration interval of a product.

Typically, delta environmental and drift is determined from empirical data gathered during the characterization phase of product development. In some cases, delta environmental and drift may be theoretically derived based on relevant data from components or materials used in a product.

Measurement uncertainty represents the possible errors associated with the equipment and the measurement techniques used during the testing of a product.

Customer guardband represents any additional guardband considered necessary to ensure that a product meets the specifications. In the majority of cases, the customer guardband is zero.

Characteristics and Supporting Specifications

Characteristics describe product performance that is useful in the application of the product, but is not covered by the product warranty. Characteristic information is representative of the product and in many cases, it may be supplemental to a specification. Characteristics are less structured than specifications. In most cases, they do not include the guardbands that are part of the specifications. Typically, determination of characteristics occurs during product development and they are not necessarily verified on all units produced.

They represent any one of the following:

The average or median value of a parameter based on measurements from a significant number of units.

A tolerance interval or proportion of a performance distribution derived from the measurement of a significant number of units. The proportion is typically greater than 80%.

A parameter with a quantity that is not subject to variation (e.g., marker resolution). It may be either non-measurable, verifiable only through (non-traceable) functional pass-fail tests, or not be routinely measured. Nonetheless, if the feature associated with this characteristic is non-operational (and so yielding unexpected performance), the product warranty covers the repair of the failure.

The quantity of a parameter that is not of significant importance to the customer (e.g., product weight).

The quantity of a parameter covered by a specification, but over a narrower range of conditions. For example, a specification describes the performance of a parameter over the 0 to 50 ºC temperature range. A characteristic may describe the same parameter but over the 20 to 30 ºC temperature range.