Both batch execution systems (BES) and manufacturing operations management (MOM) systems have been defined by mature Instrument Society of America (ISA) standards, but they are not always viewed in the same light or with the same level of favorability. In some circles, batch execution might be viewed as inferior to manufacturing execution, but might it be the other way around?
The claim demonstrates an interesting dynamic in the market for automation and supervisory control in today’s batch processing industries.
To clarify, we consider batch industries to include food & beverage, consumer goods, pharmaceuticals and similar industries where part of the manufacturing process is carried out in batch reactors. These reactors produce a batch of intermediate product at a time. Other parts of the process are likely to be more discrete and must be integrated with the batch processes to deliver final packaged product.
So what is so special about batch processes? Batch processes could be seen as an irritating block to a perfectly good discrete workflow. However, when you look in more detail at the discrete workflow, you could use batch processing techniques to handle much of it. If we look at a typical pharmaceutical tablet making process, it becomes almost classically batch-oriented from start to finish.
The key to making a tablet is the active ingredient, which is often made batch by batch. The raw materials are weighed and dispensed automatically into the batch reactor under control of the batch recipe system, and then the batch is processed with little or no human intervention. At the end, the batch is delivered into containers, and all batch historical data is included with the electronic batch record (EBR) for that product. The final product is made by weighing and dispensing active and other ingredients required to make the pills, and is passed through a semi-continuous process of tablet making. It is then packed, labeled and serialized—again, batch by batch.
When we study the process above, it is clear that batch execution is the key to correct manufacturing of our tablet. It is information that is critical to knowing what was done. Batch execution processes use information from the recipe and the process in order to run correctly. But it is the information collected as each phase of the batch runs that defines the EBR and hence the perceived and demonstrable compliance of the batch. In today’s regulated environment, batch systems will be validated quite separately from EBR systems and perhaps MOM solutions as well.
Vendors make bold claims about their use of the ISA-88 and ISA-95 standards for batch and MOM. Both standards define hierarchies of hardware and/or functionality intended to make understanding and implementing systems easier. The batch standard is particularly useful because it defines hardware from the enterprise down to processing units, and then maps hierarchical batch recipes onto that hardware model. Almost all batch systems implemented at the PLC level and below follow this method. It allows for a lot of reuse of low-level recipe phases from one recipe to another, and easy-to-understand recipe structures.
Vendors of MOM systems have not, on the whole, been quite as detailed in following the ISA-95 standard. The standard describes a multi-level hierarchy from plant equipment at Level 0 to enterprise governance at Level 5. Level 3 is the MOM layer and the functions, such as production execution, quality management, plant scheduling and data tracking, which are all described in the standard, as are interfaces between these functions. However, most MOM systems today are monolithic and encompass some or all Level 3 function in a single solution. They do, to some degree, implement standard interfaces between Level 3 and 4, but that is difficult to standardize completely because there are so many Level 4 systems with which to communicate. As Industrial Internet of Things (IIoT) technology and standards emerge, we expect this situation to change quite rapidly as individual functionality.
However, the ISA standards still have a future. A huge amount of work has been done by ISA and related organizations to define batch and manufacturing execution systems in a way that is easy to understand. The standards enable manufacturers to have a baseline from which to start their journeys in both fields. The details of the standards, especially when interfacing between different levels, have helped many implementation efforts.
It is clear that, at least in MOM, the rigid hierarchy and interfaces defined in the standard will gradually be replaced by IIoT-based platforms and architectures. We expect much of the ISA breakdown of functionality to remain similar while possibly going further into smaller functional blocks, but that is some way off.
The success of the ISA-88 batch standard will continue—one could argue that ISA-88 is the rich uncle rather than the poor relation of ISA-95. The richness provided by the physical, process and procedural models of batch execution will continue to be of great benefit even if control strategies change somewhat as the factory floor becomes ever more connected.
>>Andrew Hughes, [email protected], is principal analyst at LNS Research, with a primary focus on research and analysis in the manufacturing operations management (MOM) practice. He has 30 years of experience in manufacturing IT, software research, sales and management across a broad spectrum of manufacturing industries.
