ISA88 Part 5 draft: Control recipe phase, equipment operation
Possible language in ISA88 Part 5 draft standard, Figures 13-15, follow on control recipe phase, equipment operation, and other control concepts. Please provide comments to ensure the standard is understandable, appropriate, and useful across industries and areas of control, machine control, batch control, and continuous control, as well as flexible and scalable, across hybrid applications.
Depending upon their backgrounds and training engineers can have different views of what should be separated into the procedural and basic categories. When evaluating implementations by others sometimes the appropriateness of where a specific part of a functional strategy should exist can lead to a view that control has been blended with both procedural and basic control in and equipment phase, equipment module or control module.
With fewer modules less module to module interaction is required but it becomes more difficult to separate procedural and basic control as represented in Figure 13: Two module implementation with blended control.
The 12 module approach in Figure 14 requires more module interaction but provides possibilities for better isolation and flexibility of control as well are improved reusability.
Engineering determines how much procedural, coordination, and basic control may exist within a single module as indicated in Figure 13 and Figure 14: Twelve module implementation with more separation between control types.
When more than one FS exists within a module generally there is no clear indication of which FS is active as indicated in Figure 15: Module with multiple functional strategies.
Unrestricted access to a module can create performance issues leading to unintended actions by the functional strategy and is often constrained or not allowed.
The type of FS that focuses on equipment procedural control which is recipe aware is found in equipment phases which can be located in a unit or in an equipment module.
Equipment phases have command and control requirements and behave similarly independently of where they reside.
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– David A. Chappell, Complete Manufacturing Automation associates – LLC