What is MES?
An MES (Manufacturing Execution System) is software that drives, monitors and records the execution of production orders on the shop floor, forming the bridge between business planning in ERP and process automation with PLCs and SCADA. An MES tells operators what to make, with which materials, machines and instructions, and records what actually happened. In the ISA-95 model and the Purdue Model, MES sits at Level 3, the layer of manufacturing operations management. This makes MES a core system in OT convergence: it talks to business systems and to the control layer alike.
🧠 What does an MES do?
An MES tracks and steers everything that happens between order release and finished product:
- Executing orders — turning production orders from ERP into work orders per line, machine or workstation and releasing them in the right sequence (dispatching)
- Linking people, machines and materials — checking that the right raw material, the right tooling and a qualified operator are present
- Collecting data — counts, downtime, process parameters and measurements from the control system and from operators
- Assuring quality — recording in-process measurements, inspections and SPC, and blocking deviations before product moves on
- Tracing — recording per batch or serial number which materials, machines and people were involved
- Reporting — confirming completions, consumption and performance (OEE) back to ERP and management
📜 Which functions belong to an MES according to MESA and ISA-95?
In 1997 the industry association MESA International described eleven core functions in its white paper MES Explained: A High Level Vision, known as the MESA-11 model. It is still the most widely used functional reference framework in MES tenders and selections. In 2004 it was followed by the Collaborative MES model (c-MES), which puts more emphasis on integration with other business processes.
| MESA-11 function | What it covers |
|---|---|
| Resource allocation and status | Status and allocation of machines, tooling and materials |
| Operations/detailed scheduling | Detailed scheduling and sequencing of orders per line |
| Dispatching production units | Releasing work orders to lines and workstations |
| Document control | Work instructions, recipes and drawings at the workstation |
| Data collection/acquisition | Production and process data from control systems and operators |
| Labour management | Attendance, qualifications and hours of personnel |
| Quality management | Measurements, inspections and deviations |
| Process management | Monitoring and adjusting process steps |
| Maintenance management | Planning and executing maintenance, often via a CMMS |
| Product tracking and genealogy | Full origin and history of every product |
| Performance analysis | KPIs such as OEE, lead time and scrap |
ISA-95 (internationally IEC 62264) brought structure to Level 3. Part 3 of the standard divides manufacturing operations management into four domains: production, quality, maintenance and inventory. That is why many vendors now call their product a MOM platform rather than an MES. ISO 22400-2 (2014) defines 34 related KPIs, including OEE.
📍 Where does MES sit in the Purdue Model and ISA-95?
| Level | Systems | Time frame | Role |
|---|---|---|---|
| 4 — Business planning and logistics | ERP, MRP | Months, weeks, days | Customer orders, purchasing, finance |
| 3.5 — IDMZ | Proxies, jump servers, replicas | n/a | Controlled separation of IT and OT |
| 3 — Manufacturing operations | MES, Historian, LIMS, WMS | Days, shifts, hours, minutes | Execution, quality, traceability |
| 2 — Supervisory control | SCADA, HMI, batch systems | Minutes, seconds | Operation and visualisation |
| 1 — Basic control | PLC, DCS, RTU | Seconds, milliseconds | Control loops and machine logic |
| 0 — Process | Sensors, actuators | Continuous | Physical process |
Level 3.5 does not come from ISA-95 itself: it is a security layer added to the Purdue Model later. An MES works in near real time: it responds within seconds to minutes, but does not drive valves or motors itself. Hard real-time control stays at Level 1.
🔄 What is the difference between MES, ERP and SCADA?
| Characteristic | ERP | MES | SCADA |
|---|---|---|---|
| ISA-95 level | 4 | 3 | 2 |
| Core question | What do we produce, and when? | How do we execute this order right now? | What is the process doing at this moment? |
| Granularity | Order, item, week | Work order, batch, step, operator | Tag, measured value, alarm |
| Typical users | Planning, purchasing, finance | Shift leaders, operators, quality | Control room operators |
| Data retention | Years (financial) | Years (batch record, genealogy) | Short-term locally; long-term history in a historian |
| Example | SAP S/4HANA | Siemens Opcenter | WinCC, Ignition |
ERP knows that 10,000 units must be made, SCADA sees the process temperature, and MES knows which batch on which line, with which recipe and which operator, is producing those units.
🔧 How is an MES integrated?
- Towards ERP — ISA-95 Parts 5 and 6 describe the transactions and messages. B2MML, a set of XML schemas maintained by MESA, is the most widely used implementation for product definitions, schedules and performance reports. EDI-style batch interfaces are increasingly being replaced by APIs.
- Towards the control layer — via OPC UA, often with the companion specifications for ISA-95 (OPC 10030 for personnel, equipment and material, OPC 10031-4 for job orders). Older installations still use OPC DA.
- Batch processes — recipes follow ISA-88; the MES passes a batch order to the batch system and receives the result back.
- Unified Namespace — in modern architectures, control systems, MES and ERP publish their data to an MQTT broker in an ISA-95 hierarchy (enterprise/site/area/line). The MES then becomes one of many consumers and sources instead of the hub in a web of point-to-point interfaces.
📦 What types of MES software are there?
- Enterprise suites from automation vendors — Siemens Opcenter (formerly SIMATIC IT and Camstar), Rockwell FactoryTalk ProductionCentre and Plex (acquired in 2021), AVEVA MES, Dassault DELMIA Apriso
- Industry-specific systems — for example Körber Werum PAS-X and Emerson Syncade for pharma with electronic batch records
- ERP-related — SAP Digital Manufacturing, tightly linked to SAP ERP
- Modular and low-code — Tulip, Critical Manufacturing and the Sepasoft MES modules on the Ignition platform
🧭 How do you approach an MES implementation?
- Start with the process, not the package — map the order flow, quality checks and paper forms, and choose two or three measurable goals (for example OEE, batch record review time, scrap).
- Define the scope with ISA-95 — decide which functions belong in ERP, MES, LIMS and CMMS, so that no duplicate master data arises.
- Start with a pilot line — one line or department, often in a brownfield setting with existing PLCs. This lets you learn quickly what works before you scale up.
- Unlock the machine data — via OPC UA, an edge device or a Unified Namespace; expect extra effort for older machines.
- Validate where required — in regulated industries according to GAMP 5 (second edition 2022).
- Roll out per site with a template — a core model with local variants prevents every plant from ending up with its own MES.
💊 What do GMP and 21 CFR Part 11 mean for an MES?
In pharma, medical devices and food, the MES is often the system in which the electronic batch record (EBR) is created. Strict requirements apply:
- FDA 21 CFR Part 11 (March 1997) — electronic records and signatures are equivalent to paper, provided there are audit trails, access control and validated systems
- EU GMP Annex 11 — the European counterpart for computerised systems. A draft revision from July 2025 (consultation closed in October 2025) makes cybersecurity (patching, penetration testing, firewalls) an explicit GxP requirement for the first time.
- Data integrity — under ALCOA+, data must among other things be attributable, legible, contemporaneous, original and accurate
🔐 How do you secure an MES?
The MES sits at the intersection of IT and OT, which makes it an attractive target: if it fails, production often stops, even when the control system is still running.
- Place the MES in the OT zone at Level 3 — with an IDMZ between MES and ERP; no direct connections from the office network to the control layer
- Apply the zones and conduits model according to IEC 62443 and segment MES servers, shop-floor clients and databases
- Manage identities separately — a dedicated OT Active Directory or a strictly separated domain, with MFA for administrators
- Keep the system available — high availability, tested backups and a paper fallback procedure so production can continue
- Patch in a controlled way — through patch management and change management, with revalidation in regulated environments
For Dutch manufacturers covered by NIS2 and the Dutch Cybersecurity Act (Cyberbeveiligingswet), the MES belongs explicitly in the risk assessment and the asset inventory.
🎯 What are the benefits of an MES?
- Visibility of production — up-to-date status of orders, lines and work in progress
- Less waste and fewer errors — wrong materials or expired recipes are blocked
- Better traceability — recalls can be limited to the affected batches, essential in pharma, food and automotive
- Faster release — review by exception of the batch record instead of checking paper dossiers
- Foundation for Industry 4.0 — reliable production context for analytics, digital twins and industrial AI
❓ Frequently asked questions
What does MES stand for?
MES stands for Manufacturing Execution System. An MES is software that executes, monitors and records production orders on the shop floor. The system sits between ERP and process control.
Is an MES the same as an ERP system?
An MES is not the same as an ERP system. ERP plans at Level 4 what needs to be produced and handles purchasing and finance, whereas an MES drives execution per order, batch and workstation at Level 3. The MES reports consumption and completed quantities back to ERP.
What is the difference between MES and MOM?
MOM (Manufacturing Operations Management) is the ISA-95 term for all Level 3 activities: production, quality, maintenance and inventory. An MES traditionally covers mainly the production part. Many modern MES packages now cover the entire MOM domain and are therefore also marketed as a MOMS.
Which standard describes MES?
The main standard for MES is ISA-95, published internationally as IEC 62264. It describes the levels, the Level 3 activities and the information exchange with ERP. The MESA-11 model, B2MML and ISO 22400 for KPIs are other widely used references.
Does every factory need an MES?
Not every factory needs a full MES. Small or simple production can often manage with ERP plus OEE tracking or a modular platform. An MES pays off mainly where traceability requirements are strict, product variants are numerous, or there are multiple lines and sites.
Why does MES security matter for OT security?
MES security matters because the MES communicates with both ERP and the control layer, so it can become a bridge between IT and OT for attackers. An outage caused by ransomware, for example, often halts production. That is why an MES belongs at Level 3 behind an IDMZ, segmented according to IEC 62443.
📌 In summary
An MES is the factory’s execution system: it turns ERP orders into work on the shop floor, collects production and quality data and records the complete history of every product. It sits at ISA-95 Level 3, integrates through B2MML, OPC UA or a Unified Namespace, and needs its own place in OT security, behind an IDMZ.