Posted by: Harold Ennulat | June 21, 2010

S88: More Than Batch Control

Reviewed the book “Applying S88 – Batch Control from a User’s Perspective” by Jim Parshall and Larry Lamb,  ISA Pub, 2000.                 

S88 is the general name for the ANSI/ISA batch standard set, the first part of which has been published as ANSI/ISA-S88.01-1995.  General concepts are covered in this 157 page book with examples of how they applied these principles in a Ben & Jerry’s Ice Cream Making enterprise.                

In addition the authors have made available an online tutorial on S88 that summarizes much of what is in the book, even modifying a few concepts from the book.  http://www.batchcontrol.com/s88/tutorials.shtml             

http://www.batchcontrol.com/s88/01_tutorial/index.shtml               

Recipes are kept separate from the equipment or unit control

   

 S88 is an example of writing modular code that separates the recipe control from the equipment (or unit) control.               

The book is good for applying the standard.  Thought is still needed for any particular application.  Much of the S88 standard gives you options for putting your system together that can be omitted for particular implementations.  So even though this book does a good job at providing an application framework, it still leaves the user to map out the details for any particular implementation.  The book then is a good resource for guiding your team in mapping out your own new batch implementation.               

Recipe and Equipment Logic Flow Example: click to see enlarged view

 In current S88 batch control implementations, the batch engine is typically PC based (when using Wonderware InBatch, or Rockwells RSBatch for example).  These batch engines handle a lot of the S88 implementation frame work that allows the programmer to configure a system.  This then leaves the PLC to do what is called the “phase logic” with all the central intelligence residing in the batch engine which issues instructions such as “add ingredient: Sugar: 100lbs: +-2lbs: et.al.” and the PLC just does it and reports back the result.  This requires a robust PC environment, presumably with redundancy and automatic failover.              

The advantage of this approach is that much of the work of implementing batch control is already done by the Batch Engine suppliers leaving the programmer to learn the specific implementation and focusing on writing the PLC phase logic and interface (communications failure logic).  This also leads to more standardized and maintainable code and code that may not require any modification at all for things like assigning ingredients to storage tanks, and finished and semi finished product storage assignments.                

Additionally, while S88 is a batch standard, much of what is in the S88 standard would apply to discrete and continuous operations as well.  For example, all three types of control (discrete, continuous, and batch) have modes and states that could be implemented using the S88 (or similar standard such as PackML).  Also any kind of sequential control in discrete and continuous operations could also be implemented using the SFC (sequential function chart) programming model used in the S88 standard.                

It seems that the S88 standard practices could also apply to warehousing and truck and rail car loading and unloading operations.                

In completely custom applications I have not seen this catch on yet outside of the batching operations.  Standards however will help drive for more standardization across increasing varied types of control projects.                

However, even where this approach is used in batch applications, the approach is very different from writing straight PLC relay ladder logic and allowing the PLC to control everything.  This requires lots of discussion and buy in by all the stake holders to implement this successfully; from corporate and plant management, to IT, to purchasing and logistics, to the operators, and maintenance organizations.         

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Update: August 8, 2010:  I am making my book review notes availabe now as well after realizing that they contained additional information that would be useful in selecting and implementing an S88 system.  The link is at: https://hennulat.wordpress.com/plc-posts/applying-s88-book-review-notes/            

Updated:  August 8, 2010  5:20 pm CST  |  Created:  June 21, 2010

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Responses

  1. […] of project so this articles title caught my attention. Having just spent some time learning about how to apply S88 in practice, it seemed quite natural to apply some of the principles to my current project […]


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