Choosing between historian and MES integration
While historians and manufacturing execution systems (MES) have been around for a long time, there are still a lot of questions on how to best integrate both to maximize the benefits of each. In the past, historians have been used to store process data and allow comparison of current to past process conditions. In the last decade, this has changed. Historians have now grown into powerful, real-time calculation engines that allow context-specific analysis of a large number of assets (greater than 1 million). This allows real-time analysis of large and complex systems, such as wind farms, data centers, or turbines.
For MES, the historian mostly is used as a data source similar to structured query language (SQL), open platform communications (OPC), laboratory information management system (LIMS), supervisory control and data acquisition (SCADA), or other similar sources. This shallow integration uses only the data storage capabilities of the historian without benefitting from the real-time calculations, data conditioning, and abstraction. Figure 1 is a flowchart that shows both MES and historians in the ISA-95: Enterprise-Control System Integration functional hierarchy.
In general, there are two types of information flows in a manufacturing enterprise:
- Transactional/relational data
- Real-time data.
Transactional data are found in order processing, resource management, quality, labor, maintenance, and so on, while real-time data mostly originates from the plant floor. Real-time data bubble up from production levels (Level 0, 1, and 2) to the site and enterprise levels while changing their characteristics:
- Level 0, 1, and 2: High-frequency data: milliseconds to seconds, source-specific, noisy
- Level 3: Medium-frequency data: seconds to minutes, abstract, aggregates
- Level 4: Low-frequency data: minutes to hours, days, or weeks; abstract, aggregates.
Note that the main data transformation occurs at the historian level, where data are compressed, aggregated (min, max, total, sum, etc.), and most importantly, abstracted. Mapping performs the abstraction, for example, a controller tag TIC01234.PV to the temperature property of a reactor (e.g., reactor/temperature). A data scientist will now be able build a reactor model or predictive maintenance calculation based on the abstraction layer, instead of searching through a vast amount of uncategorized data.
For similar reasons, the MES should not consume raw production data. Its primary function is order management, production performance calculations, forecast, quality, and resource planning. But performing real-time transformations of process data on the MES itself will often lead to a loss in both performance and accuracy. Therefore, interfacing the historian with the MES should be performed on the abstraction layer (see Figure 2).
Successfully connecting the historian to the MES requires adherence to common standards, such as S95 for the equipment model and/or S88 for the batch model. The interface will replicate the data structure between systems and validate the structural integrity. The benefit of this architecture is a deep integration of historian and MES that maximizes the utility of both systems. It separates the manufacturing data flows and creates common interfaces to exchange data and structures.
Historians play a central role in the manufacturing data flow of real-time information. The main historian operations, such as data compression, de-noising, aggregation, and abstraction can benefit the enterprise data analytic as well as MES operations. This requires a deep integration of the historian by abstracting the data layer using common standards, such as S95 and S88, and interfacing with the analog MES data structures. The result is an architecture that uses both systems to the full extent of their capabilities while acknowledging the differences in the data properties and requirements.
This post was written by Dr. Holger Amort. Holger is a senior consultant at Maverick Technologies, a leading automation solutions provider offering industrial automation, strategic manufacturing, and enterprise integration services for the process industries. Maverick delivers expertise and consulting in a wide variety of areas including industrial automation controls, distributed control systems, manufacturing execution systems, operational strategy, business process optimization and more.
- The growth of historians into real-time calculation engines allows analysis of large and complex systems.
- A typical MES uses only the data storage capabilities of the historian without benefitting from the real-time calculations, data conditioning, and abstraction.
- Interfacing the historian with the MES should be performed on the abstraction layer.
How robust is the historian/MES integration in your plant?
Maverick Technologies is a CSIA member as of 3/29/2016
This article has been adapted for use in the Control Engineering July 2016 Inside Process section of articles.