S88 Batch Control Standard – Letico Inc.
S88 Batch Control Standard has been developed under the auspices of the ISA (the Instrumentation, Systems, and Automation Society) and is the appropriate Standard to apply in many Batch Process Control or Automation projects. Like any Standard it does require knowledge of the Standard and forces extra discipline in completing a project but the resulting benefits well justify any extra time required. Letico does promote and recommend the use of the S88 Batch Control Standard and is involved in some of the ongoing work to refine and extend the Standard.
Potted Description of ISA – S88 Batch Control Standard
The S88 standard provides a common terminology for batch manufacturing. It uses two main models which describes the Physical and Procedural make-up of a batch manufacturing process. The Physical Model is used to describe equipment, and the Procedural Model describes recipe process sequencing. In this way the batch manufacturing standard provides a separation of recipe procedure and equipment control logic.
S88 defines Recipes, which describe products and how those products are produced. Recipe procedures reside on a PC, while the programming code running the production equipment resides in the PLC or DCS residing within the equipment. When it comes time to make a product, the manufacturing requirements defined by the recipe and its procedure are linked to the required equipment. The recipe phase within the PC batch server communicates with the equipment phases via a set of protocols held in the PC. These protocols define the states the equipment may function in, e.g. idle, active, pause, stop etc, and the possible transitions between states. A Phase Logic Interface (PLI) resides in the PLC or DCS system to enforce these transition protocols and communicate back and forth with the PC.
A series of modules are available to exercise monitoring, control and management functions with titles such as:
- Control Activity Model
- Recipe Management
- Production Planning and Scheduling
- Production Information Management
- Process Management
- Unit Supervision
Because S88 isolates recipes from equipment, recipes can be edited without modifying PLC code. Moreover, recipes can run on different sets of equipment. This generates significant cost and implementation-time reductions through effective utilization and optimization of plant equipment. Data collection, tracking and genealogy are also benefits of S88 batch control. All process steps within a recipe procedure are time stamped, and actual values are stored and referenced to the batch. Raw materials, associated characteristics and quantities consumed are automatically logged to the batch journal.
Since the official issue of the S88.01 standard in 1995, there have been many success stories in batch manufacturing. The standard provides the foundation for faster time-to-market, improved product quality management and reduced production costs.
For a more complete understanding of ISA S88 Batch Control Standard, the references given below will be found useful.
For more information about ISA standards, visitwww.isa.org/standards.
S88 and batch processing – selling the standard – April 2004
Writing a Functional Specification for an S88 Batch Project
August 01, 2003 Christie Deitz, Todd Ham and Steve Murray
Access only to subscribers
Applying ISA-S88 to Software Migration Engineering – Dow Chemical