Open Architectures to Improve Plant Visibility and Performance

Manufacturers have invested heavily in automation infrastructure, yet much of it remains islands of automation: information silos disconnected from each other and from business systems. This whitepaper by Fulvio Roveta examines open architecture in industrial automation as the alternative to point-to-point integration, comparing two dominant approaches, OPC and Service Oriented Architecture (SOA), and showing what each delivers in practice.

The opening section quantifies the point-to-point problem. For interconnected systems, the number of point-to-point interfaces required is n(n-1)/2 - ten interfaces to fully connect five automation islands, where a common infrastructure needs five, with the gap widening quadratically as points increase. Research findings are cited on the share of IT budgets spent building point-to-point interfaces and maintaining automation islands. The benefits of the infrastructure approach are set out as robustness (widely tested, multi-vendor, off-the-shelf components), flexibility (islands keep producing data in native formats while interface software translates), and communication (real-time transport with the same data version available to all users, without polling).

OPC is introduced as the most widely used real-time connectivity standard in industrial automation and process control: a client-server model in which a server written once for a device can be reused by any OPC client, covering real-time data, historical data and alarms and events. The paper is equally direct about its historical constraint, OPC Classic specifications built on Microsoft COM/DCOM, and classifies the resulting issues as security (large dynamic port ranges above 1024, Port 135 for the initial handshake, no NAT traversal, callbacks opening reversed connections that default firewalls block), robustness (activation failures taking up to three minutes as each network protocol is tried in turn) and set-up complexity (most vendor support calls trace to DCOM and Windows Security configuration, which can take weeks over a WAN).

SOA is then examined on its own terms: autonomy and interoperability, contract-based loose coupling, outside-in interface design, Web Services and .NET Remoting, along with its criticisms around processing overhead and evolving standards.

Two case studies close the paper. The first is an automated emergency advisory system for a large oil producer's refined-products distribution network, built on a three-tier .NET Remoting architecture integrating SCADA OPC DA/HDA servers, relational databases, plant historians and an expert system. The second consolidates ten DCSs and plant historians onto OPC with redundant virtualised OPC servers, fault-tolerant clients and OPC tunneling software converting COM calls to .NET.