OPC DA
OPC DA (OPC Data Access) is an industrial communication standard based on Microsoft COM/DCOM technology for Real-time data exchange between Industrial Automation systems. The standard was developed to enable interoperability between PLCs, SCADA systems, HMIs, historians and other OT applications from different vendors.
OPC DA played a central role within Industrial Automation for many years and remains an important part of many legacy OT environments. Despite the rise of OPC UA, OPC DA is still widely used in existing industrial infrastructures because of broad compatibility with older systems.
Within modern IT OT Convergence architectures, OPC DA often acts as a transitional technology between legacy OT systems and modern industrial data platforms.
⚙️ What is OPC DA
OPC DA stands for:
OLE for Process Control Data Access
The standard was developed by the OPC Foundation in the 1990s and uses Microsoft technologies such as:
- COM
- DCOM
- OLE
- RPC
The primary goal of OPC DA is standardised real-time access to process data.
Examples of data:
- process values
- statuses
- alarms
- setpoints
- temperature measurements
- motor states
- IO statuses
🏗️ Architecture of OPC DA
OPC DA uses a client/server model.
Architecture:
PLC / Device
│
OPC Server
│
DCOM
│
OPC Client
Important components:
| Component | Function |
|---|---|
| OPC Server | Interface to field equipment |
| OPC Client | Data consumer |
| COM/DCOM Layer | Communication |
| Device Driver | Protocol translation |
The OPC server translates vendor-specific protocols into a uniform OPC interface.
🔌 Communication principles
OPC DA uses Microsoft COM/DCOM for communication between processes and systems.
COM
COM (Component Object Model) provides local communication between applications.
DCOM
DCOM (Distributed COM) enables network communication.
This allows OPC clients and servers to run distributed across different systems.
📡 Real-time data exchange
OPC DA supports real-time process data.
Important functions:
| Function | Description |
|---|---|
| Read | Read values |
| Write | Write process values |
| Subscribe | Receive changes |
| Polling | Cyclic reading |
| Callbacks | Event-driven updates |
Most SCADA systems use subscriptions to reduce network load.
🧠 OPC DA data model
Within OPC DA, process values are organised as tags or items.
Examples:
Boiler1.Temperature
Line3.Motor.Speed
Pump2.Status
Each Tag contains:
| Property | Meaning |
|---|---|
| Value | Process value |
| Timestamp | Timestamp |
| Quality | Data quality |
Quality codes are essential for OT systems.
Examples:
- Good
- Bad
- Uncertain
This allows operators to assess whether data is reliable.
⚡ Polling versus subscriptions
OPC DA supports multiple communication models.
Polling
The client periodically requests data.
Benefits:
- simple
- predictable
Drawbacks:
- higher network load
- inefficient on large systems
Subscription-based updates
The server only sends updates on changes.
Benefits:
- more efficient
- lower network load
- near real-time behaviour
Within large industrial environments, subscriptions are dominant.
🔄 OPC DA and industrial protocols
OPC DA often acts as an abstraction layer above industrial protocols.
Common couplings:
| Underlying protocol | Use |
|---|---|
| Modbus | PLC communication |
| Modbus TCP | Ethernet industrial communication |
| Profibus | Legacy fieldbus |
| ProfiNET | Modern industrial Ethernet |
| Ethernet IP | Industrial networks |
| S7 Comm | Siemens PLC communication |
| BACnet | Building automation |
The OPC server handles protocol translation.
🖥️ OPC DA within SCADA
OPC DA became the standard interface for many SCADA platforms.
Applications:
- real-time monitoring
- process visualisation
- Alarm Management
- Historian data collection
- reporting
- Trending
Typical architecture:
PLC
│
OPC Server
│
SCADA
│
Historian
This allowed SCADA systems to communicate vendor-neutral.
📦 OPC DA servers
Many vendors deliver OPC DA servers.
Examples:
| Vendor | Product |
|---|---|
| Kepware | KEPServerEX |
| Siemens | SIMATIC NET |
| Schneider Electric | OPC Factory Server |
| Matrikon | OPC Server |
| Rockwell | RSLinx OPC |
These servers often support hundreds of industrial protocols.
☁️ OPC DA and IT/OT convergence
Within modern architectures, OPC DA often functions as a legacy integration layer.
Common couplings:
| System | Integration |
|---|---|
| MES | Production data |
| Historian | Time-series storage |
| ERP | Business integration |
| MQTT | Edge publishing |
| OPC UA | Protocol migration |
Many modern gateways convert OPC DA to more modern protocols.
⚠️ DCOM issues
One of the biggest drawbacks of OPC DA is its dependence on DCOM.
Issues:
| Issue | Impact |
|---|---|
| Firewall complexity | Difficult configuration |
| Dynamic ports | Security issues |
| Windows dependency | Limited platform support |
| Complex authentication | Management burden |
| Network sensitivity | Instability |
DCOM is known as difficult to manage within industrial networks.
🔒 Cybersecurity risks
OPC DA was designed in a time when OT networks were largely isolated.
Modern Security mechanisms are therefore lacking.
Important risks
| Risk | Impact |
|---|---|
| Unencrypted communication | Data theft |
| Weak DCOM configuration | Unauthorised access |
| Windows vulnerabilities | Remote compromise |
| Legacy servers | Unpatched systems |
| Lateral movement | OT compromise |
🛡️ Hardening of OPC DA
Important security measures:
- Network Segmentation
- Industrial Firewall
- DCOM hardening
- minimal privileges
- dedicated service accounts
- Patch Management
- Logging
- Security Monitoring
Many organisations place OPC DA servers within a DMZ.
📡 OPC DA versus OPC UA
OPC UA was developed as the successor to OPC DA.
| Property | OPC DA | OPC UA |
|---|---|---|
| Technology | COM/DCOM | Platform-independent |
| Operating system | Windows-only | Multi-platform |
| Security | Limited | Built in |
| Encryption | No | Yes |
| Firewall-friendly | Difficult | Better |
| Data model | Simple | Extensive |
| Cloud integration | Limited | Strong |
Despite these differences, OPC DA remains broadly present in existing OT environments.
🔄 Migration to OPC UA
Many organisations gradually migrate to OPC UA.
Typical strategies:
- OPC DA wrappers
- protocol gateways
- parallel infrastructures
- phased migration
- edge gateways
Migration challenges:
- legacy PLCs
- old SCADA systems
- vendor lock-in
- validation requirements
- downtime risks
🧪 OPC DA in OT labs and simulation
OPC DA is still widely used in:
- test environments
- simulation platforms
- OT labs
- training environments
Benefits:
- broad compatibility
- large installed base
- easy integration with Legacy Systems
⚡ Performance considerations
Benefits
| Property | Result |
|---|---|
| Mature technology | Stability |
| Broad support | Interoperability |
| Real-time subscriptions | Low latency |
| Vendor-neutral | Flexibility |
Drawbacks
| Issue | Consequence |
|---|---|
| DCOM overhead | Higher complexity |
| Windows dependency | Limited flexibility |
| Firewall issues | Difficult management |
| Legacy security | Higher risks |
🏭 Practical applications
Manufacturing
Use for:
- machine monitoring
- line control
- SCADA integration
- historian collection
Energy supply
Applications:
- substation monitoring
- turbine control
- energy management
Water sector
Use for:
- pumping stations
- remote Telemetry
- process monitoring
Building Automation
Integration of:
- HVAC
- energy management
- building monitoring
🛡️ Relevant standards and guidelines
| Standard | Relevance |
|---|---|
| IEC 62443 | OT security |
| NIST SP 800-82 | ICS cybersecurity |
| ISA-95 | IT/OT integration |
| NIST CSF | Cybersecurity governance |
Legacy OPC DA environments increasingly fall under stricter cybersecurity requirements.
📈 Trends and developments
Important developments:
- migration to OPC UA
- edge protocol gateways
- OPC tunneling
- Unified Namespace
- MQTT integration
- cloud-native OT
- OT protocol abstraction
Although OPC DA is being slowly phased out, it will remain relevant within industrial legacy environments for years.
🎯 Conclusion
OPC DA was the dominant standard for industrial real-time data exchange for many years and formed the basis for interoperability between PLCs, SCADA systems and industrial software.
Despite limitations around DCOM, cybersecurity and platform dependency, OPC DA remains deeply Embedded in many existing OT infrastructures. Within modern IT OT Convergence architectures, OPC DA often functions as a transitional technology towards more modern standards such as OPC UA.
For industrial organisations, good management, segmentation and controlled migration remain essential to keep legacy OPC DA environments operating safely and reliably.