Specification Variables

A specification defines the target value and various upper and lower quality and alarm limits for a variable and a product combination. It can be used to define the amounts of materials in a batch process, measure the actual value of a quality variable against a target and set of limits, or compare the current values of a set of process-related variables against the average of a number of past sets.

Specifications are defined for a specific product. They can be as general or detailed as needed and can be specific to a production line and unit, or they can be shared across many production lines and units.

Unit Variables

Variables are attached to a specific piece of equipment and describe the individual parameters controlled or measured on that piece of equipment. Unit variables can be attached to specification variables if their recipe is not machine / equipment specific.

Recipes

Within Plant Applications, a broad definition of a recipe is employed. Within the scope of the plant, a recipe or product specification can take on many meanings. Plant Applications models product information in a generic way to allow for all types of product information to be stored.

A recipe is a concept that describes and details the attributes of a product. A product's attributes provide knowledge about the product, such as:

The production unit to which the product is assigned
The steps to manufacture the product
The materials used to manufacture the product
When to accept or reject a product
The process control settings used
The test procedures to use
When to test a product or measure its attributes

Plant-Level Recipe Maintenance

Plant-level recipe maintenance can be performed by entering specifications for properties and characteristics. Specifications entered at this level are automatically propagated to the individual products and units (equipment) that are associated with that property and characteristic. It is common to maintain quality specifications at the plant level because, in most situations, these specifications are not equipment specific. It is also common for quality specifications to have a one-to-one relationship between characteristics and actual products.

Unit-Level Recipe Maintenance

Unit-level recipe maintenance can be performed by entering specifications for a production unit or variable group. Specifications maintained at this level are equipment specific. Specifications maintained at the plant level may be overridden at the unit level to handle specific exceptions.

How To Decide Between Plant Level And Unit Level Recipe Maintenance