ISA88 Part 5 draft: Traditional automation designs for batch recipes
A series of discussions follow seeking input on possible language in ISA88 Part 5 draft standard, Figures 1-5 follow. Please provide comments at the bottom of this posting 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.
To help in understanding the focus of Part 5 it is beneficial to discuss some of the dominate traditional approaches used to design, develop and deliver automation used to support ISA 88 batch recipes. The following discussion points provide insight into many of the different traditional approaches used in delivery of ISA 88 modular systems and contrasts those approaches with the recommendations of Part 5.
- Traditional Equipment and Control Modules are custom engineered composites of automation components designed to meet the requirements of a functional strategy (FS) as represented in…
Figure 1: Traditional Automation Module.
- A functional strategy may consist of a totally custom design and implementation or it may utilize components provided by the suppliers of the automation control equipment as represented in Figure 2, which uses a function block provided by a vendor to implement a motor starter. The IEC 61915-2 specification provides methods to interact with function block described as part of that standard and can significantly reduce the amount of custom effort required to implement a FS. As indicated in Figure 2 there is generally additional functionality required to deliver the FS than is provided by the function blocks and the engineer must add that functionality and the methods to interact with the FS of that module. Often the methods and interfaces provide by the function blocks are not appropriate for general use and as part of the additional functionality the module must manage what is exposed and mange interaction with the components used to deliver the FS.
Example of some additional functionality: Simulation, management of permissives and interlocks, ability to bypass the function block and manipulate the outputs directly (Part 1 Automatic and Manual Mode), initialization functionality, alarm management, etc.
Figure 2: FS using vendor supplied function block
- Traditional modules may contain clearly defined methods that allow them to be commanded and controlled from an external source to carry out the functional strategy as represented in Figure 3. In some instances the interactions are obscure and require deep understanding of the FS implementation to be able to interact with it as indicated in Figure 4.
Figure 3: Clearly defined command and control
Figure 4: Obscure command and control
- Command and control encompasses all the external interfaces, data in, status and data out, and commands to activate or change states and behavior as indicated in Figure 5: Command and Control Interfaces.
Figure 5: Command and Control Interfaces
- These command and control methods are generally custom and are generally deep within the custom automation and require detailed understanding of the FS and the implementation to successfully interact with the module.
Next post will discuss Figures 6-12.
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