OPC Client vs OPC UA Client: Key Differences Explained

OPC Client vs OPC UA Client: Key Differences Explained—

Industrial automation relies on reliable communication between devices, controllers, and software. Two terms you’ll often encounter are “OPC Client” and “OPC UA Client.” At first glance they seem similar, but they refer to different technologies and capabilities. This article explains their key differences, when to use each, and practical considerations for implementation.

What is OPC?

OPC originally stood for OLE for Process Control. It began in the 1990s as a set of standards to allow Windows-based industrial software (like SCADA, HMI, and historians) to communicate with automation hardware (PLCs, RTUs, drives) using a common interface. The original and widely used specification is now called OPC Classic, which includes interfaces like OPC DA (Data Access), OPC HDA (Historical Data Access), and OPC A&E (Alarms & Events).

What is OPC UA?

OPC Unified Architecture (OPC UA) is a modern, platform-independent evolution of OPC Classic. It was designed to address limitations of the older specs, add security, and enable richer information modeling. OPC UA unifies data access, historical access, and alarms/events into a single framework and supports cross-platform operation (Windows, Linux, embedded systems, mobile).

Core technical differences

Architecture & Platform Support

OPC Classic relies on Microsoft COM/DCOM technology, making it largely Windows-centric. It depends on Windows networking features and is harder to use across firewalls or with non-Windows systems.
OPC UA is platform-independent, using a binary TCP protocol and optional HTTPS/WebSockets, making it suitable for Windows, Linux, and embedded devices.

Security

OPC Classic has limited security; DCOM configuration is complex and often insecure if misconfigured.
OPC UA includes built-in security: authentication, authorization, encryption, and signing. Security policies and certificates are first-class features.

Data Model & Information Modeling

OPC Classic focuses on simple data access structures (items/tags) with limited semantic context.
OPC UA supports rich information modeling, allowing devices to expose structured object models, types, metadata, relationships, and semantics — useful for Industry 4.0 and digital twin scenarios.

Communication & Protocols

OPC Classic uses COM/DCOM and is sensitive to network topology and firewalls.
OPC UA supports multiple transports (UA-TCP, WebSockets, HTTPS) and binary or XML encodings, providing flexibility and better performance over networks.

Interoperability & Extensibility

OPC Classic has many vendor-specific implementations; interoperability often requires additional middleware or configuration.
OPC UA is designed for interoperability, with well-defined profiles and standardized information models (e.g., PLCopen, OPC UA for Machinery).

Scalability & Performance

OPC Classic can perform well in local Windows-only environments but struggles when scaling across diverse networks or platforms.
OPC UA scales better for large, distributed systems, and offers optimized binary encodings and session management for high-performance needs.

Practical differences for users

Deployment environment

If your environment is strictly Windows and uses legacy systems or software that only supports OPC DA/HDA/A&E, an OPC Classic client may be required.
For new deployments, cross-platform needs, cloud integration, or security-sensitive applications, OPC UA is the preferred choice.

Security requirements

For projects requiring modern security (TLS, certificate management, role-based access), OPC UA provides the necessary features out of the box.
OPC Classic may require network-level controls and careful DCOM setup to reach acceptable security.

Integration with modern technologies

OPC UA integrates more naturally with IoT, cloud platforms, and modern MES/ERP systems due to its information models and transport options.
OPC Classic often needs gateways or wrappers to bridge into modern architectures.

Maintenance and future-proofing

OPC Classic is legacy technology; many vendors still support it, but new development and standards focus on OPC UA.
Selecting OPC UA helps future-proof integration projects, especially where industry standards and digital transformation are priorities.

Migration considerations (OPC Classic → OPC UA)

Inventory: List devices, servers, tags, and client dependencies on OPC Classic.
Compatibility: Check whether devices/PLCs and third-party software offer native OPC UA or require wrappers/gateways.
Security: Plan certificate management and network changes for UA endpoints.
Data mapping: Map classic items/tags to OPC UA address space and information models; consider enhancing metadata.
Testing: Validate performance, authentication, and failover scenarios.
Phased rollout: Run OPC Classic and OPC UA in parallel where possible to reduce risk.

Example use cases

Legacy SCADA connecting to older PLCs on a local Windows server: OPC Classic client may be adequate.
Distributed plant with Linux-based edge gateways sending secure telemetry to cloud and MES: OPC UA client is the right choice.
Machine vendor exposing device models and diagnostics to enterprise systems: OPC UA’s information modeling enables richer integration.

Comparison table

Aspect	OPC Classic (OPC Client)	OPC UA Client
Platform	Windows (COM/DCOM)	Platform-independent
Security	Limited; DCOM-based	Built-in: TLS, certs, auth
Data model	Simple items/tags	Rich information modeling
Transports	COM/DCOM	UA-TCP, HTTPS, WebSockets
Interoperability	Vendor-specific quirks	Designed for interoperability
Firewall traversal	Difficult	Easier with modern protocols
Future-proofing	Legacy	Modern standard

Recommendations

Choose OPC UA for new systems, especially when security, cross-platform support, cloud connectivity, or rich data models matter.
Use OPC Classic only when constrained by legacy software or devices that cannot be upgraded, and plan migration to OPC UA when feasible.
Consider gateways/wrappers as transitional solutions to bridge OPC Classic servers to OPC UA clients.

OPC Client vs OPC UA Client: Key Differences Explained