What Is a Manufacturing Execution System (MES)? Modules, Selection and Setup

MES is the production tracking system that follows how an ERP work order runs on the shop floor. Its place in ISA-95, modules, the data problem on machines without a PLC, and selection criteria.

Translated from the Turkish original · Türkçe aslı

A production tracking system, or MES (Manufacturing Execution System), is software that monitors, records and manages in real time how a work order opened in ERP is carried out on the shop floor. What was produced on which machine, how long it stood still, how many good and defective parts came out, and which batch of material was used are all collected in MES. In the ISA-95 model it sits between ERP and the automation layer.

Below we explain which tasks MES takes on in a factory, where the data comes from, and what to look for in selection and implementation. How video analytics data is technically connected to MES is covered separately in our MES integration article.

Are MES and a production tracking system the same thing?

In everyday use they mostly describe the same thing, but their scope can differ. A "production tracking program" sometimes means a simple application that only records work orders, production quantities and downtime. MES is a broader concept: it covers all production operations, from dispatching work orders to the floor to quality records, from material traceability to maintenance and performance analysis. In the standards, the term manufacturing operations management (MOM) is also used for this layer. When evaluating software, look at which functions it actually delivers rather than at its name.

Where does MES sit between ERP, SCADA and PLC?

The reference model that defines the boundary between enterprise systems and automation systems is ISA-95; its international counterpart is the IEC 62264 standard. The model views the factory in five levels: from the physical production process (Level 0) to the automation layer with PLCs, SCADA and sensors (Levels 1 and 2), to manufacturing operations management where MES sits (Level 3), and to business planning and logistics where ERP sits (Level 4).

The most practical way to separate the levels is the time scale. ERP works in months, weeks and days: it plans what will be produced, with which materials and by what date. The automation layer works with control loops of a second and below. MES works in between, in days, shifts, hours, minutes and seconds: it breaks the plan down to shifts and machines, collects what actually happens on the floor and reports back to ERP. ERP knows that a work order is open; it is MES that knows which machine that work order is on right now, which part it has reached and why it has stopped.

Here is how the flow works for a single work order. ERP sends a 2,000-unit work order to MES with the bill of materials and due date. MES splits the work order across shifts and a suitable machine, and pushes it to the operator screen together with the work instructions. When production starts, the machine's run signal, counter and stops flow into MES from the automation layer or another data source. At the end of the shift, MES reports the good quantity produced, the scrap and the material consumed to ERP; ERP updates stock and cost accordingly. (The figures are illustrative.)

What does MES do?

The most frequently cited framework describing the functions of MES is the eleven-function model published by MESA International in the late 1990s (MESA-11). These functions can be broadly grouped into four areas.

Planning and dispatching: detailed scheduling, dispatching work orders to machines and stations, and tracking the status and allocation of resources such as machines, tools, materials and personnel.

Recording and traceability: data collection from the floor; product tracking and genealogy, which record which steps a product passed through with which materials and batches; and control of documents such as work instructions, drawings and recipes.

Quality and process: quality management covering measurement, inspection and non-conformance records; process management, which routes the workflow according to the plan; and maintenance management.

Labour and performance: labour management by shift and competence, and performance analysis comparing actual results with the plan. OEE is the best-known indicator in this group.

Which modules does a production tracking system include?

Products offer these functions in different packages, but the modules most often encountered on the floor are similar:

• Work order and operator terminal: the operator starts and finishes the work order and enters quantity and scrap.
• Downtime tracking and OEE: start, end and reason code of each stop; breakdown into availability, performance and quality.
• Quality: measurement entry according to the control plan, non-conformance and quarantine records.
• Traceability: the link from the raw material batch to the serial number of the finished product.
• Material and line feeding: line-side stock and consumption records.
• Maintenance: breakdown reporting and the planned maintenance schedule.
• Reporting: dashboards by shift, line and product.

Which module is needed first depends on the plant's pain point. In a factory where downtime is invisible, the first gain comes from the downtime and OEE module; we explain the calculation logic step by step in our how to calculate OEE article. For a supplier whose customer demands batch-level traceability, the priority is the traceability and quality module; in a workshop where work orders circulate on paper, the work order and terminal module comes first.

A common question is whether ERP's production module can take the place of MES. ERP production modules generally work at work-order level: a work order is opened, production is confirmed and material consumption is posted. Shop-floor details such as the machine's minute-by-minute status, the reason for a stop, or which part was produced with which batch usually fall outside the scope of these modules. If what you need is quantity and cost tracking per work order, the ERP module may be enough; if you need downtime, OEE and part-level traceability, you need an MES layer.

Where does the data come from? Machines without a PLC and manual stations

The least discussed but most time-consuming part of an MES project is data collection. On a modern machine, status, counter and alarm information can be read from the PLC via standard protocols such as OPC UA. In most plants, however, the machine park is mixed: a twenty-year-old press, a machine tool whose PLC cannot be accessed, an injection moulding machine that is not networked and fully manual assembly stations stand side by side.

In this situation there are three options. The first is to fit additional hardware to the machine: an input module that reads the counter signal for quantity, and a current sensor to tell whether it is running. This works, but every machine means separate cabling and electrical work. The second is operator entry: quantity, stops and reasons entered at the terminal. It is cheap, but the data is only as accurate as the operator's time and attention allow; short stops are usually never entered. The third is video: a camera that sees the machine or station derives run status, cycle time and quantity from the image; it produces data without touching the PLC or even fitting a sensor. On machines that do have PLC data, the two sources are combined and validate each other. For protocol-level details, see our IoT and video integration article.

Whatever the data source, the list of downtime reasons must be set up well from the start for the data to be meaningful. A list of hundreds of items pushes the operator towards the top option; a list of only a few items collects every stop under "other". The structure that works has two levels: a small number of main groups such as breakdown, die change, waiting for material, quality and planned stop, and under each group the sub-reasons the floor actually uses. The list is corrected during the pilot by looking at the share of "other".

What should you look for when choosing an MES?

Before the feature list, write down your own question: which decision do you expect to make with data from MES in the first year? Then an evaluation can be made against the following criteria.

Fit with production type: discrete part manufacturing, batch production and continuous processes require different data models. The needs of a chemical plant requiring recipe and batch management are not the same as those of an automotive supplier tracking serial-numbered parts.

Data collection capability: ask how the system will get data from machines without a PLC and from manual stations, which protocols it supports and how much additional hardware it requires. A system that connects to every machine on paper may fall back to operator entry on older machines in practice.

Integration and adaptability: exchange of work orders, materials and production confirmations with ERP; connections to quality, maintenance and warehouse systems; a data model aligned with ISA-95 concepts and an open API. Changes such as the downtime reason list, control plan and screen flow should be possible through configuration without a developer; a system that turns every change into a software project cannot change along with the factory.

Architecture and usability: whether the system will run on-premises or in the cloud, what the floor will do during a network outage, and how it will be segregated from the OT network. The simplicity of the operator screen, local support and training options also determine whether the system will actually be used on the floor.

What are the steps of an MES implementation?

Implementation generally proceeds in six steps:

1. Goal and indicator: which line, which decision, which metric.
2. Inventory: machine list, each machine's data source (PLC, signal, operator or camera) and network status.
3. Master data: bill of materials, routing, ideal cycle times, downtime reason and defect code lists; the quality of these lists determines the quality of the reports.
4. Pilot line: go-live on a single line, operator training, and comparing what the system shows with what happens on the floor during the first weeks.
5. ERP integration: receiving work orders and confirming production.
6. Rollout: moving to other lines with the definitions that settled in the pilot.

Implementation time varies over a wide range depending on the size of the plant, the diversity of the machine park and the number of integrations. The most frequent cause of delay, however, is master data rather than the software: products with unknown ideal cycle times, stations coded differently in two systems, downtime reasons whose meaning varies from person to person. We describe a similar step plan for video analytics in our implementation process article.

How do MES and video analytics work together?

Video analytics does not replace MES; it supplies data where MES is weakest. On a machine without PLC data it measures downtime and cycle time (OEE with cameras). At a manual assembly station it derives active work, waiting and line-balancing losses by station, without linking them to individuals (PPA). On a packaging line it completes traceability with video evidence by matching the image of each product 1:1 with its product ID (video evidence system). Each event flows into MES with a timestamp, station ID and event type; MES suspends the work order, opens a quality record or updates OEE.

Where to start?

At CX Teknoloji we do not sell MES software; we install video analytics that supplies data to your existing MES or ERP. In the default setup, video is processed on an edge server inside the facility, events are published via REST API and MQTT, and face recognition is not used. If you do not yet have an MES, downtime and cycle data measured by cameras becomes baseline data during selection, showing which module you need first. For a pilot starting with the single line where data collection is hardest, get in touch with us.

Frequently asked questions

What is the difference between MES and ERP?

ERP plans at company level: orders, purchasing, stock, cost and what will be produced. MES manages how this plan is carried out on the floor: which machine the work order started on, stops, the good and defective quantities produced, the material batch used. ERP works in days and weeks, MES in shifts, hours and minutes. The two systems complement each other; MES reports actual production back to ERP.

Are MES and SCADA the same thing?

No. SCADA is the automation layer that monitors and controls machine and process data in real time; it shows a line's alarm or a tank's level. MES builds the production meaning of this data: which work order, which product, how many units, which downtime reason. In the ISA-95 model, SCADA sits at the automation levels, MES at the third level and ERP at the fourth.

Does a small factory need MES?

The need depends more on the type of problem than on the size of the factory. Any plant where downtime and scrap reasons are invisible, where the customer demands batch-level traceability or where work orders circulate on paper benefits from production tracking. At a small scale, starting with downtime, OEE and work order tracking instead of a full-scope MES, and adding modules as needs become clear, is a more realistic path.

How is data sent to MES from machines without a PLC?

There are three ways: fitting additional hardware such as a counter and current sensor to the machine, having the operator enter data at a terminal, or deriving run status, cycle time and quantity from the image of a camera that sees the machine. Additional hardware requires cabling, and operator entry misses short stops. A camera produces data without touching the PLC; if PLC data exists, the two are combined and validate each other.

How long does an MES implementation take?

The duration varies with the size of the plant, the diversity of the machine park, the data sources and the number of systems to be integrated; giving a single figure would be misleading. It usually starts with a single-line pilot and is rolled out to other lines once the definitions have settled. The most frequent cause of delay is master data: making ideal cycle times, station codes and downtime reason lists consistent across two systems.

What is the most important criterion when choosing an MES?

What matters most is whether the system can actually collect data from your data sources. An MES with no solution for machines without a PLC and for manual stations falls back to operator entry and incomplete data on the floor. In addition, fit with production type, ERP integration, configurability without a developer and the simplicity of the operator screen should be assessed together.