If you write software that touches a factory, you'll hear "ERP", "MES" and "SCADA" in the same sentence, often as if they were interchangeable. They aren't. The ISA-95 standard describes manufacturing systems in levels, and each of these three lives at a different one, working on a very different timescale.
ERP: the business level (ISA-95 level 4)
Orders, inventory, materials, finance and planning, measured in days and weeks. ERP decides what should be made and when.
Examples: SAP S/4HANA (SAP) and Plex Smart Manufacturing Platform (Rockwell Automation), which spans ERP and MES.
MES and frontline apps: manufacturing operations (level 3)
Dispatching work orders, tracking production, genealogy, quality and OEE, measured in shifts and hours. MES turns the ERP plan into actual work on the shop floor and reports back what really happened.
Examples:
- Siemens Opcenter, AVEVA MES, Proficy Plant Applications (GE Vernova), FactoryTalk ProductionCentre (Rockwell Automation)
- Critical Manufacturing MES, Sepasoft MES Modules (on top of Ignition), Parsec TrakSYS
- Frontline-app and OEE tools such as Tulip and MachineMetrics
Side-by-side comparisons: Sepasoft vs Tulip, AVEVA MES vs Opcenter, Critical Manufacturing vs Opcenter, Proficy Plant Applications vs Opcenter, Tulip vs TrakSYS, Tulip vs Plex, MachineMetrics vs TrakSYS.
SCADA and HMI: supervisory control (level 2)
Live monitoring and control of equipment, measured in seconds. SCADA shows operators what machines are doing right now and lets them act on it.
Examples: Ignition (Inductive Automation), SIMATIC WinCC and WinCC Unified (Siemens), FactoryTalk View and FactoryTalk Optix (Rockwell Automation), AVEVA System Platform and AVEVA InTouch HMI, Proficy iFIX and Proficy CIMPLICITY (GE Vernova).
Comparisons: Ignition vs WinCC, Ignition vs AVEVA System Platform, AVEVA InTouch vs FactoryTalk View.
Where the lines blur
In practice the boundaries overlap: some ERPs ship shop-floor modules, some SCADA platforms add MES modules, and frontline-app platforms cover parts of MES. So the label on the box matters less than one question: which system is the source of truth for each piece of data?
A common pattern is orders flowing down from ERP to MES, MES dispatching to the line, SCADA reporting live machine state up, and MES sending production confirmations back to ERP. If you're connecting all of this through a broker, the Unified Namespace stack guide walks through that architecture, and the process historian checklist covers where the time-series data ends up.
Questions to answer before choosing
- Which system owns work orders, and which owns actual production counts?
- How do orders flow down and confirmations flow back up (API, files, middleware)?
- Do you need a full MES, or would OEE or frontline apps cover the gap?
- Is the plant regulated (for example pharma or food) and in need of electronic batch records?
Vendor capabilities change, so always confirm integrations and modules in each vendor's current documentation.
This is a cross-post from PlantWired, a free, vendor-neutral directory of which factory software works with what. The full guide lists every ERP, MES and SCADA tool in the directory with its documented integrations, and you can subscribe to the newsletter there for new comparisons. Corrections are very welcome in the comments.
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