MES explained: what a manufacturing execution system does, where it sits between the ERP and the control systems, and what it is called in mining and process plants
What a manufacturing execution system does, the MESA functions and the four IEC 62264-3 operations areas, MES beside the ERP, historian, CMMS and control systems, the production management, reporting and metallurgical accounting systems that fill the role in mining and process plants, one agreed set of shift numbers, and the questions to settle before buying or building. With a drawing of MES in the ISA-95 levels.
Key takeaways
- A manufacturing execution system, or MES, runs the plan on the plant floor and records what actually happened. It sits between the ERP that plans the business and the control systems that run the process.
- ISA-95, published internationally as IEC 62264, places MES at level 3 and divides it into four operations areas: production, quality, maintenance and inventory.
- In mining and mineral processing the same job is usually called a production management or production reporting system, with metallurgical accounting and stockpile management alongside.
- The value is in decisions made from one set of shift numbers: losses by cause, actuals against plan, and traceability. An MES that only replaces a spreadsheet report is an expensive report.
- Most of the cost and risk of an MES is in its interfaces to the control systems, historian, ERP and CMMS, and in agreeing where each number comes from.
A processing plant reports three different tonnages for the same night shift. The control room's figure comes from the weightometer in SCADA, the production report from a spreadsheet the supervisor fills in, and the ERP from the stockpile survey at month end. Each is defensible and none agree, so the morning meeting spends its first twenty minutes on which number is right instead of on why the plant lost two hours.
This guide explains what a manufacturing execution system is, the functions it covers, where it sits in the ISA-95 model beside the ERP, historian, CMMS and control systems, what it is called in mining and process plants, and the questions to settle before buying or building one. It sits beside the guides to system integration, the data historian and PLC, DCS and SCADA. The standards named are reference points.
Where MES sits
ISA-95, published internationally as IEC 62264, describes a plant in levels. The business systems at level 4 plan on a horizon of days to months. The control systems at levels 1 and 2 run the process in seconds. Level 3, manufacturing operations management, is the layer between, and an MES is the software that fills it.
Plans and orders come down from the ERP, and the MES turns them into a schedule the plant can run, releases the work, and watches it. Actuals go back up: what was produced and consumed, what quality it was, what was lost and why. IEC 62264-3 divides the layer into four operations areas, production, quality, maintenance and inventory, each with the same pattern of scheduling, dispatching, execution, data collection, tracking and analysis.
The ERP says what should happen this month. The control system makes it happen this second. The MES says what happened this shift, and why.
What an MES does
MESA International's functional model, first published in the 1990s and folded into ISA-95, gave the classic list of what an MES does. Few sites need all of it. Most start with data collection, downtime and performance analysis, because those turn the plant's own data into the losses that management acts on, and add quality, tracking and scheduling as the need is proven.
| Function | What it does | What it gives the site |
|---|---|---|
| Detailed scheduling | Turns the plan from the ERP into a sequence by unit, line or shift | A shift schedule the control room can run |
| Dispatching | Releases orders or targets to the plant and tracks them as they start and finish | Work released in the right order, with the current status visible |
| Data collection | Gathers production counts, tonnes, rates, states and quality results from the control systems and people | One set of numbers for the shift, not three |
| Tracking and genealogy | Follows material and product through each step, with the batches, lots or stockpiles it came from | Traceability when a quality problem has to be traced back |
| Quality management | Holds the test plans, records sample results and releases or holds product | Product released on evidence |
| Performance analysis | Compares actuals with plan, and calculates availability, rate and quality losses | The losses shown by cause, by shift and by unit |
| Downtime and states | Records when each unit was running, stopped or slowed, and why | A downtime record that adds up |
| Resource and labour | Tracks the people, skills and equipment assigned to each unit | Crewing matched to the schedule |
| Document control | Delivers the current procedures and instructions for each order or unit | The right instruction at the point of use |
MES beside the systems around it
An MES is defined as much by what it is not. It does not control the plant, store high resolution process data or run the business, but it depends on the systems that do. Each boundary needs to be agreed, because the most common MES failure is two systems doing the same job and producing two answers.
| System | Its job | Time horizon | Relationship to MES |
|---|---|---|---|
| ERP | Level 4: the business plan, orders, costs, purchasing and finance | Days to months | Sends the plan down, receives the actuals |
| MES | Level 3: running the plan on the plant floor and recording what happened | Shifts, hours and minutes | Between the business and the control systems |
| Historian | Level 3: storing time-series process data at high resolution | Seconds | Supplies the process data MES calculations use |
| CMMS | Level 3 or 4: maintenance work, assets, history and spares | Days to weeks | Takes defects and runtime from MES, gives back planned outages |
| SCADA, DCS and PLCs | Levels 1 and 2: controlling and supervising the process | Milliseconds to seconds | Receive setpoints and targets, send counts and states |
What MES is called in mining and process plants
The term MES comes from discrete and batch manufacturing, and many mining and processing sites do not use it at all. The same functions are delivered by systems with industry names, often several of them covering parts of the MES layer between them. Knowing the mapping helps when comparing products or explaining the architecture to people who have only ever used one of them.
| Name | Where it is used | What it covers |
|---|---|---|
| Production management system | Mining and processing | Plans, targets and actuals by shift for the mine and plant |
| Production reporting or accounting | Mining, mineral processing | The tonnes, grades and hours reported each shift and month |
| Metallurgical accounting | Mineral processing | Mass and metal balances that reconcile the mine, plant and product |
| Stockpile management | Bulk materials and ports | Tonnes and grade in each stockpile, built and reclaimed |
| Batch execution system | Food, chemicals, pharmaceuticals | Recipes run by batch under ISA-88, with the batch record |
| Laboratory information management system (LIMS) | All process industries | Often the quality part of MES, run as its own system |
One set of numbers
The quiet value of an MES is a single agreed figure for each measure. Tonnes for the shift come from one weightometer with one calibration, downtime from one record with one set of downtime codes, and availability, rate and quality losses from one calculation, the same one the OEE calculator uses. Each measure needs a source, a calculation, a time base and an owner, written down before any software is chosen.
Maintenance belongs in the same picture. Run hours and starts from the MES drive usage based maintenance in the CMMS, defects captured in the shift log become work requests, and planned outages come back from the CMMS so the production plan knows about them.
Before buying or building
MES projects have a reputation for running long, and most of the overrun is in the interfaces and in arguments about numbers that should have been settled first. A short list of questions, answered before any product is chosen, avoids most of it. The technology stack guide covers the build side in more depth.
| Question | Why it matters |
|---|---|
| What decisions will it change? | If nobody would run the shift differently with the numbers, an MES only automates a report |
| Where does each number come from? | Each measure needs a source, a calculation and an owner before any software is chosen |
| What does the ERP already do? | Overlap between ERP and MES modules causes two versions of the truth |
| Which parts are standard? | Downtime, production reporting and quality are well served by products. Site-specific logic may be cheaper to build |
| How will it be integrated? | The interfaces to the control systems, historian, ERP and CMMS are most of the work. ISA-95 gives the shared model |
| Who will run it? | An MES needs an owner and support for the life of the plant, not just a project team |
Where MES projects go wrong
- Bought to replace a report, with no decision that the new numbers will change.
- Measures defined by the software's defaults rather than by the site, then argued about for a year.
- Production recorded in both the ERP and the MES, with different answers.
- Interfaces to the control systems and historian left until late, then found to be most of the work.
- Downtime codes copied from another site, so the losses do not match how this plant fails.
- Every function bought at once, so none of them is used well.
- No owner after go-live, so the configuration drifts from how the plant actually runs.
Common questions
What is an MES?
A manufacturing execution system is the software that manages and records production on the plant floor. It takes the plan from the ERP, schedules and dispatches it to the plant, collects what was produced, consumed and lost, tracks material and quality, and reports the actuals back. In the ISA-95 model it is level 3, manufacturing operations management, between the business systems at level 4 and the control systems at levels 1 and 2.
What is the difference between MES and ERP?
The ERP runs the business: orders, purchasing, inventory value, costs and finance, on a horizon of days to months. The MES runs production: the shift schedule, dispatching, data collection, quality and performance, on a horizon of shifts, hours and minutes. The ERP sends the plan down and the MES sends the actuals back. Problems start when both try to do the same job, such as recording production, and produce two answers.
What is the difference between MES and SCADA?
SCADA supervises and controls the process: it shows operators the plant, raises alarms and sends commands to PLCs, in seconds. An MES manages production: what should be made, what was made, what was lost and why, by shift and order. The MES takes counts, states and process values from SCADA and the historian, and may send targets or setpoints back, but it does not control the plant.
What does an MES do?
The MESA functional model lists the core functions: detailed scheduling, dispatching, data collection, product tracking and genealogy, quality management, performance analysis, resource and labour management, process management, maintenance management and document control. IEC 62264-3 groups the same work into production, quality, maintenance and inventory operations, each with scheduling, dispatching, execution, data collection, tracking and analysis.
What is a production management system in mining?
In mining and mineral processing the MES role is usually filled by a production management or production reporting system. It holds the shift plan and targets for the mine and plant, records tonnes, grades, hours and delays, and feeds metallurgical accounting, which reconciles what was mined, processed and shipped. The functions are the same as an MES, described in the industry's own terms.
Key terms
Plain-language definitions from our glossary for the concepts this article leans on.
Standards and further reading
Related case studies and tools
- OEE Calculator (tool)
- Real-time production analytics (case study)
Related reading
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