Applying S88: Book Review Notes

These are the notes I used to prepare an earlier post entitled “S88: More Than Batch Control“.  I reviewed these notes and realized that there is much more detail here that a programmer would need to be aware of to form his own S88 selections and implementations.  It is for this reason that I have now included them.

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What follows are my notes after reading and reviewing “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, only some of which has now been published (ANSI/ISA-S88.01-1995).  General concepts are covered in this 157 page book with examples of how they applied them in a Ben & Jerrys Ice Cream Making enterprise.

Topics discussed are the Recipes, Equipment, and how you link recipes to equipment.  There are a number of concepts discussed within this such as the Physical Model (Enterprise may contain many Sites, each Site may contain many Areas, which may contain many Process Cells, which must contain one or more Units, which may contain many Equipment Modules, which can contain other Equipment Modules, which may contain many Control Modules, which may contain other Control Modules.

Recipe and Equipment procedures, each consisting of: Procedure which contains an ordered set of Unit Procedures, which consists of an ordered set of Operations which contains an ordered set of Phases.

Phase Logic can break down into a series of control steps, with each control step broken down further into control actions.  A control action should perform simple independent actions like opening a valve, specifying a set point, or performing a calculation.  Control Steps would then be a logical grouping of control actions.  One way to write Phase Logic is to think of a control step as a rung of logic with each output as a control action.

Phases can be described in tables with a column for the control steps and another for control action.  Each table would be a phase.

Phases can also be described in SFCs (Sequential Function Charts).  The author suggests using Visio or AutoCad and also possibly from a PLC SFC export of some kind.  (Is this really available?).

Also a spreadsheet can be used to write convincing looking SFC’s with outlining added to flesh out any necessary details on what happens (is changed) in a step.

Modes and States: The above Phase Logic discussion is part of the “running” state.  The phase logic states are Running, Holding, Restarting, Stopping, Aborting.

S88 suggests 12 procedural states and 8 procedural commands.  (Ref figure 8.1,  table 8.4 and 8.5).

Writing Control Modules.  These are a collection of sensors, actuators and even other control modules and associated process equipment that operates as a single entity.  This code should handle automatic and manual modes, Simulation mode, permissives, Alarms.

Batch Management Model:  Includes Recipe Management, Production Planning and Scheduling, Production Information Management, Process Management, Unit Supervision, Process Control, and even Personnel and Environmental Protection (though this last point is outside of the scope of S88).

Today, only the Phase logic is executed in the PLC.  The rest of the batch control is run in a batch server, presumably a redundant batch server.  This batch server PC setup is part of RSBatch or InBatch (Wonderware).  The beauty of this is  that most of the S88 structure is already built in to the Batch application.  This leaves the programmer to learn just the specific implementation of the batch engine and the PLC phase logic.

Something called PLI is also needed in the PLC.  PLI is Phase Logic Interface logic which monitors the connection to the Batch engine and then takes default actions if communications are lost.  Sample PLI software is often provided by the Batch application vendors.

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

The other concept mentioned was the idea of separating ingredients with ingredient storage so that any storage tank can contain any possible ingredient with assignment being made by plant personnel rather then requiring PLC programmers to make these changes. 

This is another level of recipe, an equipment setup recipe.  The main product recipe then would not need to know where the ingredient is coming from.

This can also be applied to semi finished or final product storage tanks.  This concept could also be extended to warehousing, truck and train loading and unloading stations.

Any discussion about equipment can also be applied to a unit or a functional collection of equipment.

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Published: August 8, 2010  2:05 pm CST  |  Created June 18, 2010  8:40 pm CST

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