TABLE OF CONTENTS A key feature of the S88 Automation Design Pattern is a specific pattern for organizing control logic in automated systems. This pattern can be applied using the IEC 61131-3 languages or traditional computer languages. The pattern separates control logic into three different forms of control: coordination control, procedural control, and basic control. These forms of control are implemented in a hierarchy of equipment control objects: process cells, units, equipment modules, and control modules. Each element of the equipment hierarchy performs one or more of the types of control for specific purposes. A combined equipment control hierarchy and recipe control hierarchy is shown back in Figure 5-2.
The top level of the equipment hierarchy is the process cell. The process cell contains all of the equipment to make a batch. A process cell is made up of units, shared equipment modules, shared control modules, and common control modules. The process cell contains coordination control to create control recipes, manage batch-to-unit associations, and to create and update the batch record. The process cell also contains procedural control to interpret control recipes.
Units are the next level of the equipment hierarchy. Batches are assigned to units and there is, at most, one batch per unit. Units contain equipment modules and control modules, and units expose equipment phase interfaces. Units and their phase definitions provide the interface between recipe-execution systems and equipment control. Units contain coordination logic that manages communication between the externally visible equipment phases (unit) to the internal equipment phases...
