MES vs ERP vs SCADA: Roles and Boundaries Explained

In manufacturing digitalization, confusion often arises around three core systems:

ERP (Enterprise Resource Planning)
MES (Manufacturing Execution System)
SCADA (Supervisory Control and Data Acquisition)

Many factories invest in these systems but still struggle with data gaps, manual reporting, and unclear responsibilities. The root cause is usually a misunderstanding of roles and boundaries.

This article explains what each system does, where it stops, and how they connect, with clear diagrams to make the architecture easy to understand.

1. The Core Question Each System Answers

A simple way to differentiate ERP, MES, and SCADA is by the questions they are designed to answer:

System	Main Question
ERP	What should the business plan and report?
MES	What is happening in production right now?
SCADA	What is the machine doing at this exact moment?

They are not competing systems. They operate at different levels of time, data, and responsibility.

2. ERP: Business Planning and Enterprise Control

ERP systems manage the business side of manufacturing.

ERP Responsibilities

Production planning and scheduling
Material requirements (MRP)
Inventory, purchasing, sales
Cost accounting and financial reporting
Long-term KPIs

ERP Characteristics

Time horizon: days to months
Data granularity: aggregated
Users: planners, management, finance
Not real-time

ERP determines what should be produced, when, and at what cost — but it does not control or monitor execution on the shop floor.

3. SCADA: Real-Time Machine Monitoring and Control

SCADA operates close to the physical process.

SCADA Responsibilities

Real-time machine monitoring
Sensor and signal acquisition
Alarms and interlocks
Supervisory control commands
HMI visualization

SCADA Characteristics

Time horizon: milliseconds to seconds
Data granularity: raw signals and tags
Users: operators, automation engineers
Hard real-time behavior

SCADA knows how machines behave, but it has no understanding of production orders, customers, or business impact.

4. MES: The Execution Layer Between Business and Machines

MES exists because ERP and SCADA speak very different languages.

MES Responsibilities

Work order execution and tracking
WIP visibility
Quality checks and traceability
Downtime and OEE calculation
Operator instructions and confirmations

MES Characteristics

Time horizon: minutes to hours
Data granularity: contextualized production data
Users: supervisors, production and quality teams
Near real-time

MES answers the critical question:

“Is production being executed correctly, efficiently, and according to plan?”

5. How ERP, MES, and SCADA Connect (Conceptual View)

The diagram below shows who talks to whom and why.

flowchart TD
    ERP["ERP<br/>Business Planning<br/>Orders · MRP · Cost"]
    MES["MES<br/>Execution & Monitoring<br/>WIP · Quality · OEE"]
    SCADA["SCADA<br/>Supervision<br/>Alarms · Signals"]
    PLC["PLC<br/>Control Logic"]
    MACHINE["Machines<br/>Sensors · Actuators"]

    ERP -->|"Production Orders<br/>BOM · Routing"| MES
    MES -->|"Actual Results<br/>Qty · Scrap · Time"| ERP

    MES -->|"Work Instructions<br/>Context"| SCADA
    SCADA -->|"Status · Events"| MES

    SCADA -->|"Control Commands"| PLC
    PLC -->|"I/O Signals"| MACHINE
    MACHINE -->|"Sensor Feedback"| PLC

Key idea:
ERP never controls machines directly, and SCADA never manages business logic.
MES is the translator and coordinator.

6. ISA-95 Manufacturing Pyramid (Industry Standard View)

ISA-95 is the global standard that defines these boundaries.

flowchart TB
    L4["Level 4<br/>ERP<br/>Business Planning"]
    L3["Level 3<br/>MES<br/>Manufacturing Operations"]
    L2["Level 2<br/>SCADA / HMI<br/>Supervisory Control"]
    L1["Level 1<br/>PLC / Controllers"]
    L0["Level 0<br/>Physical Process<br/>Machines & Sensors"]

    L4 -->|"Orders · Plans"| L3
    L3 -->|"Results · KPIs"| L4

    L3 -->|"Production Context"| L2
    L2 -->|"Events · Status"| L3

    L2 -->|"Commands"| L1
    L1 -->|"Signals"| L0
    L0 -->|"Measurements"| L1

This structure explains why MES cannot be skipped without consequences.

7. Clear Role Boundaries (Summary Table)

Aspect	ERP	MES	SCADA
Primary role	Plan & report	Execute & monitor	Control & measure
Time scale	Weeks–months	Minutes–hours	Milliseconds–seconds
Data type	Orders, cost, inventory	WIP, quality, OEE	Signals, alarms
Real-time	No	Near real-time	Yes
Machine control	No	Limited	Yes
Business reporting	Yes	Partial	No

8. Common Misunderstandings

“ERP can replace MES”

ERP lacks real-time execution visibility and shop-floor context. Customizing ERP to act like MES usually increases cost and complexity.

“SCADA already gives us production data”

SCADA provides signals, not meaning. MES adds order, product, operator, and quality context.

“MES is only for large factories”

SMEs often gain the biggest benefit because MES replaces Excel, manual logs, and tribal knowledge.

9. Why These Boundaries Matter

Factories that blur system boundaries often experience:

Over-customized ERP systems
Underused SCADA data
Manual reconciliation and reporting
Low OEE accuracy
Audit and traceability issues

Factories that respect boundaries gain:

Cleaner architecture
Lower long-term cost
Better scalability
Trustworthy production data

10. Final Takeaway

ERP, MES, and SCADA form a complete manufacturing digital stack:

ERP plans the business
MES executes and monitors production
SCADA controls machines

When each system focuses on its role and integrates properly, manufacturers achieve real-time visibility, operational control, and reliable business insight — without unnecessary complexity.