ANSI/ISA-88

ANSI/ISA-88 of kortweg ISA-88 is een internationale standaard. Het helpt industrie�n om flexibel te kunnen produceren. De standaard bestaat uit modellen en termen die het productieproces logisch indelen en de besturing van het machinepark regelen. S88 kan worden toegepast in volledig geautomatiseerde, semigeautomatiseerde en zelfs in volledig handmatige productieprocessen.

What ISA-88 realy is

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:

1. Control can be fully manual (operator driven)
2. Control can be fully automatic (computer driven)
3. Control can be some combination of both (somewhere in between fully manual and fully automatic)

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.

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.

It�s this modularization that enables both flexibility and reuse of recipe components and equipment control components (often implemented via control systems and software).

ISA-88 Physical model

Enterprise

On the highest level the Enterprise is situated. The enterprise is responsible for determining what products will be manufactured, at which sites they will be manufactured, and in general how they will be manufactured. There are many factors other than batch control that affect the boundaries of an enterprise. Therefore, the criteria for configuring the boundaries of an enterprise are not covered in the S88 standard. More information can be found in the S95 standard.

Site

An enterprise is a collection of one or more sites. A Site is a physical, geographical, or logical grouping determined by the enterprise. The boundaries of a site are usually based on organizational or business criteria as opposed to technical criteria. Again there are many factors other than batch control that affect these boundaries, so it is not covered in this standard. More information can be found in the S95 standard

Area

A site may contain several areas.
An Area is a physical, geographical, or logical grouping determined by the site.

Again there are many factors other than batch control that affect the boundaries of an area, so it is not covered in this standard. More information can be found in the S95 standard.

Process cell

An area may contain several process cells. A Process Cell is a logical grouping of equipment that includes the equipment required for production of one or more batches. It defines the span of logical control of one set of process equipment within an area. The existence of a process cell allows for production scheduling on a process cell basis, and also allows for process cell-wide control strategies to be designed, which can be particularly useful in emergency situations.

Unit

A Unit is made up of equipment modules and control modules. The modules that make up the unit may be configured as part of the unit or may be acquired temporarily to carry out specific tasks.

One or more major processing activities � such as react, crystallize, and make a solution � can be conducted in a unit. It combines all necessary physical processing and control equipment required to perform those activities as an independent equipment grouping. It is usually centered on a major piece of processing equipment, such as a mixing tank or reactor. Physically, it includes or can acquire the services of all logically related equipment necessary to complete the major processing task(s) required of it. Units operate relatively independently of each other.
A unit frequently contains or operates on a complete batch or material at some point in the processing sequence of that batch. However, in other circumstances it may contain or operate on only a portion of a batch. The standard presumes that the unit does not operate on more than one batch at the same time.

Equipment module

Physically the Equipment module may be made up of control modules and subordinate equipment modules. An equipment module may be part of a unit or a stand-alone equipment grouping within a process cell.
An equipment module can carry out a finite number of specific minor processing activities such as dosing and weighing. It combines all necessary physical
processing and control equipment to perform those activities. It is usually centered on a piece of processing equipment such as a filter. Functionally, the scope of the equipment module is defined by the finite tasks it is designed to carry out.

Control module

A Control module is typically a collection of sensors, actuators, other control modules, and associated processing equipment that, from the point of view of control, is operated as a single entity. A control module can also be made up of other control modules.

State diagrams

State transition diagram for a unit/machine at the unit level

State transition diagram for procedural elements

State transition diagram for the equipment phase

Receipe based software

Physical structure