Best Practices for Implementing a Process Control Driven MES System

Emerson's Jonathan Lustri


Author: Jonathan Lustri

I have previously been interviewed and written about a process control and MES [Manufacturing Execution Systems] architecture where the batch control logic within the process control system is the single procedural engine. It drives procedural logic and workflows executed by the MES system when called by the process control system. The benefit of this architecture is an overall lower cost of ownership since after the initial implementation, and changes to the process based on new products can be most implemented by only modifying the process control system.

I am nearly completed with a project using this architecture and would like to share best practices for implementing this architecture.

Architecture after Basic Design Phase

This architecture should be developed only after a basic design phase where process maps are developed defining the high-level functions and integration touchpoints between the two systems. This should be completed before any functional specifications are developed. In this architecture, MES workflows are functions that are called by the batch logic for manual activities that cannot be performed by the process control system.

Examples of these functions are filter change, electrode calibration, equipment preparation, and solids material charging. A complete list of the needed workflow functions should be defined during the basic design phase. If the project is still defining these functions while at the same time writing functional specifications, the project will likely struggle. A complete library of the project’s MES Core Functions (MCFs) should be defined before any of the projects functional specifications are written. In this architecture the Batch Control system and MES systems functional specifications cannot be written in silos and this is why the overall process mapping, including both systems, should be developed before any functional specifications are written.

A careful process must be undertaken to develop the MCF library and to educate the project personnel regarding the objects in the library and how they should be used within the process. Each MCF must be developed with flexibility on how they operate in order to serve a wide variety of applications within the process.

For example, there are many types of filters and how a workflow may need to execute to perform a filter change may be variable depending where in the process it is executed. Such variability in how a workflow must execute should be understood early in the project.

Define Standardized Work Processes

Also, the process engineers must be part of the process to define the standardized work processes, and there must be an oversight process to overrule a process engineer that insists that in his area, something has to be different. Once the MCFs are defined, the process and automation engineers need to be educated in what they are and how they are applied.

This should be one of the first activities done before writing functional specifications. If the process control engineer writing the functional specification that includes MES workflows calls does not have a solid handle of the workflows capabilities, they will be misapplied and then rework will be required during implementation.

Preparing for Factory Acceptance Tests (FATs)

A final best practice for this architecture is how to prepare for FATs. FATs should include component level FATs where objects are tested at lower levels (e.g. Filter Change workflow), and an integrated FAT should be planned to test the process control software and how it calls the workflows. While it could be considered that actually executing the workflows is not needed from the process control systems, we have found that some details get discovered that otherwise would not be identified. It takes a lot of effort the plan and schedule both component level and integrated FATs. Master data is needed such as the sample plans and bill of materials to execute a fully integrated FAT. It is a judgement call if this is needed before the software gets to site, but no doubt doing so will reduce the issues discovered on site.

In conclusion, the process control driven architecture for MES functions will require a special level of planning and management to assure success. It begins during the early stages of the project to define process maps and the MCF library. All process control and process engineers involved in defining procedural logic must be educated on the MCF library and their functions, and detailed planning and scheduling is required to successfully execute integrated FATs.

From Jim: You can connect and interact with other MES experts in the Operations Management group in the Emerson Exchange 365 community and/or at the Oct. 1-5 Emerson Exchange conference in San Antonio, Texas.