What really is S88, anyway?
In this section you will learn
- A definition for S88
- The philosophy behind S88
- The first three principles of the standard
- Three elements of batch control
Here’s a two-sentence definition that you can give to your peers or boss (it’s a mouthful, but it works):
S88 defines hierarchical recipe management and process segmentation frameworks, which separate products from the processes that make them. The standard enables reuse and flexibility of equipment, and provides a structure for coordinating and integrating recipe-related information across the traditional ERP, MES, and control domains.
S88 isn’t just a standard for software, equipment, or procedures; it’s a way of thinking, a design philosophy. Understanding S88 will help you better design processes and manufacture products. Leveraging the knowledge and experience contained in the standard will enable you to better identify customer needs, make recipe development easier, and help reduce the time needed to reach full production levels with a new system or for each new product. Following the concepts explained in S88, you could improve the reliability of operations and reduce the automation life cycle cost of batch processes, including lowering the initial cost of automating your operations.
Despite what S88.01 may say in print, since Part 1’s release in 1995, there has been a lot of good work done both clarifying the meaning of the standard and building on what was only started when it was first issued. Some people in industry have identified a handful of basic rules, or principles, on the intent of the standard (or at least the intent of the committee that wrote it). So, before we go diving into some details in this tutorial, we thought it might be helpful to toss out a few of the principles.
Principle 1: The concept of control has a specific meaning
We’ll define control as an activity that makes equipment do things. Control must occur, but it doesn’t matter how:
- Control can be fully manual (operator driven)
- Control can be fully automatic (computer driven)
- Control can be some combination of both (somewhere in between fully manual and fully automatic)
Figure 1: The Concept of Control
In other words, keep in mind that S88 was designed to handle all levels of automation. That is, the standard can be applied to a fully-automated system or to a completely manual system…or anything in between.
Principle 2: Separate the recipe from equipment control
The enabling ability of S88 to isolate recipes from equipment is a significant technical strength of the standard. A recipe drives the process for making a product (or otherwise sequencing work in a non-manufacturing application). Control drives equipment behavior, as we mention briefly above. These are two very different activities and concepts. There is no need to think of them as one.
Figure 2: Separate Recipe and Equipment Control
In traditional control systems, it’s easy to have the software that defines a product and the software that runs equipment to end up in the same device, like a programmable logic controller (PLC) or distributed control system (DCS). The problem is when both types of software are in the same device, the two different sets of code eventually become indistinguishable, and in some cases inseparable. This makes recipes and equipment control difficult, if not impossible, to maintain. Every new product added, change in ingredient, or process improvement can require far too many person-hours to modify the software.
In a manufacturing process, if recipes are kept separate from equipment control, the manufacturing process is more flexible and can present a more appealing scenario: engineers can specify or design equipment control based on the full capabilities and the performance of the equipment, not based on requirements of a product or products. Similarly, the person who manages the recipe –scientists, product specialists, or process engineers– can create it and make changes to it directly. When a new product is launched or a product recipe needs changing, why should the product expert have to come to the automation engineer for changes, if no new equipment is needed?
Principle 3: Everything breaks into pieces
One of the key aspects of S88 is it enables the segmentation of processes. We can also call this the modularization of processes. The recipe and the process are made up of smaller pieces. The recipes is made up of concentric parts, the first level being called Unit Procedures. The process (or equipment) is made up of modules, the first level being called Units.
Figure 3: Everything Breaks Into Pieces
It’s this modularization that enables both flexibility and reuse of recipe components and equipment control components (often implemented via control systems and software).
Okay, so you were just given an explanation of S88 at the 20,000 foot level, including being introduced to three key principles. Now, let's start diving deeper.
To properly develop a successful batch control system, you need to define three important elements:
- How to make the product (recipes)
- What physical tools are needed to make the product (equipment)
- How to run that equipment (control activities)
Next, we’ll learn about the first element: recipes.