This first part in this blog series provided some explanation of MES and its symbiosis with ISA-88, and made the case for better integration between MES and plant-floor automation systems. This follow-up post will delve into more details about designing an automation system according to ISA-88 principles and the corresponding benefits to an MES implementation.
ISA-88 improves design
What is ISA-88?
The automation industry has never been willing to rest on its laurels, and is constantly seeking better ways to realize more effective process control. The industry has made great strides over the last couple of decades toward achieving standardization upon “best practices” methodologies like ISA-88. Short for the internationally accepted ANSI/ISA-88 batch control standard, ISA-88 does for process control what OPC does for communications. Like OPC, ISA-88 is a thoughtfully developed object-oriented design approach that creates appropriate structure and modularity for process functions, and defines a framework that enables communal development of cross-compatible tools and solutions from multiple vendors.
ISA-88 first began as a way to define and standardize the interface between process control and recipe execution, but has since evolved into a common design approach for batch, continuous and discrete manufacturing systems alike. The standard has also been normalized in recent years to achieve tight interoperability with ANSI/ISA95, the standard for enterprise-control system integration (well-known to MES implementers).
Simplification is good
A first-time cursory reading of the ISA-88 standard can create the impression that the design methodology described there is complicated. However, more detailed study proves quite the opposite. The object-oriented principals upon which this approach is based are intended to simplify system design by breaking down components into clearly identified pieces.
Using a technique called encapsulation, a virtual box is drawn around each functional chunk. Inside the box is all the process or equipment-related functionality (with details hidden from view), and around the box’s edge are the interface points connecting it to other pieces of the system. By hiding inconsequential details, a simplified model of interaction between components can be realized – and more importantly – visualized and understood.
Matching process actions with production activities is intuitive and sustainable
The next logical progression for creating object interfaces is to closely match them with physical or procedural parts of the process (and the key integration points for the MES). This adds inherent familiarity for process engineers or operating personnel, maximizing their useful design input and simplifying training. The resulting solution is more intuitive to use, maximizing the system’s productivity, effectiveness and ease of change over its lifecycle.
Plant personnel are essential
Team participants vary
With all the discussion today about lifecycles, it’s hard to ignore the notion that good MES solutions must be sustainable. Change is inevitable, and implementation of that change is harder to accomplish after a system’s initial roll-out. Project teams are disbanded after initial success is achieved, with each member moving on to the next challenge. As a result, future changes to a system often fall to people who weren’t involved in the original effort. Even if participating, original members may have forgotten details of the design and have to re-learn specific aspects necessary to accomplish the change – and often with a minimal allotment of time. So even if integration with the automation system was sufficiently covered in the system’s conception, it becomes harder with each subsequent iteration and the passing of time to maintain proper attention to detail.
Sustainability requires collaboration and continuity
Enter the plant automation engineer. Unlike IT folks who are project-focused, plant engineers are often dedicated to specific processes or areas of the plant, and can add an important measure of consistency. When these resources are deeply involved in the conception of an MES solution, they can readily “own” that system’s upkeep and improvement over its normal lifecycle. When new IT participants are brought in for revisions, the plant engineer can provide the necessary continuity and depth of familiarity to make sure integration details aren’t overlooked.
MES projects focused on directly supervising the execution of production steps can and should incorporate details of the plant automation systems as part of a comprehensive design approach that leaves nothing to chance. All MES implementation strategies require some degree of integration, with the depth of that integration greatly affecting the quality of the result.
Efficiency of project execution is improved with the use of an ISA-88-styled approach, and adding comprehensive system design to the equation maximizes the completeness of results and greatly improves sustainability as well – all highly desired attributes of business improvement efforts.
A best-practices approach like ISA-88 is seldom the wrong choice for marrying plant-floor automation with MES supervision, yet often isn’t the default choice. Time and business pressures that drive both innovation and adoption of best practices will eventually resolve that dilemma; but in the meantime, producers who embrace this methodology now will reap its benefits and improve their competitive edge.