This new series of columns offers a structure for implementing automation strategies based on the S88 standard.

THE GROWING CHALLENGES OF TODAY'S MANUFACTURING environment-everything from reducing the time to market for new products to customizing existing products for specific client needs-have led process industries to increasingly turn to open systems for automation and batch control. Designed to apply to sustaining flexible manufacturing practices not only in batch but also in discrete and continuous industries, ANSI/ISA-88 (S88) has proven to be the most effective way to describe and communicate automation strategies to meet these competitive needs. The modular structure and standard terminology of S88 improve communications and understanding by product engineering, plant personnel and vendors. If we understand and use the components of S88, the result will be more effective controls implementations at lower total cost of ownership that are easier to maintain and can be scaled to meet changing plant and market requirements.

Applying S88

First, it's necessary to understand how S88 is applied. The standard is independent of the underlying control system (PLC, DCS or PC), the basic control algorithms and how the processing is controlled or sequenced. It applies to manual, semi-automated and fully automated systems and is applied under these basic conditions:

• Flexible manufacturing (including batch)
• Multiple products manufactured using the same set of equipment
• Output is a finite quantity of materials and a production record
• Built using a defined order of processing actions.

Further, the ANSI/ISA-88 standard consists of four parts:

• S88.01: Models and Terminology
• S88.02: Data Structures and Guidelines for Languages
• S88.03: General and Site Recipes Models and Representation
• S88.04: Production Record.




Separating recipes and equipment

Prior to the 1995 release of ANSI/ISA-88.01, Batch Control Part 1: Models and Terminology, there were no common terminology and/or models to help transform product manufacturing requirements into parameters for production workflows and process control. Thus, integrating solutions within your own plant or from different suppliers was difficult.

By separating product knowledge in recipes from equipment capabilities, S88 allows recipe development without process control knowledge. Operators can respond to recipes without detailed knowledge of equipment control and control system engineers don't need to have detailed knowledge of recipes to optimize equipment control. The end result is flexible manufacturing based on utilizing the same equipment and process to produce multiple products of different scale.



Improved system configuration

Before S88's 1995 release (and, for the most part, as it exists today), manufacturing design had no commonly accepted elements for batch control. As a result, manufacturing systems were (and still are) difficult to build and configure. By helping to define models and terminology for flexible batch recipe management and execution systems, S88 solves these problems. The standard provides:

• a model for batch (work order, lot) control that separates recipe and equipment capabilities
• all users and vendors with the same terminology for requirements and functionality, respectively
• integration using the S88.02 data structure
• SQL Standard tables for recipes, equipment, schedules, and batch history
• data exchange through the World Batch Forum (www.wbf.org) developing XML schema, Batch Markup Language (BatchML)
• a standard language for recipe representation which makes system configuration and design easier.




Additional benefits

During the past eight years in which S88 has been in use, the World Batch Forum reported several realized benefits including a 20 percent reduced cost for automated systems with a shift from special to standard products. The time required to implement and change systems had also been reduced by 30 percent. And, the time necessary for new product definitions (recipes) had been significantly reduced from days to hours.

The benefits come from applying reuse and best practices across multiple new product introductions. S88's "n" to "many" approach applies equally well to simple and complex processes (i.e. bi-directional scalability). The models and subsequent design templates are expandable if additional levels of structure are required and collapsible if all of the model levels of structure are not. The clear lines of vertical demarcation provided by S88 lead to improved departmental communication and the tools necessary to meet the challenges of today's process manufacturing environment.