OPC Introduction
OLE for Process Control (OPC) is a standards-based approach for connecting data sources (e.g. PLCs, controllers, I/O devices, databases, etc.) with HMI client applications (graphics, trending, alarming, etc.). It enhances the interface between client and server applications by providing a universally supported and well-documented mechanism to communicate data from a data source to any client application. Included are not only a detailed guide on how to pass the data, but also specific information on other attributes to supplement those data, such as range information, data type, quality flags, and date and time information.
OPC UA or Unified Architecture unites legacy OPC standards such as OPC-AE (Alarms and Events), OPC-DA (Data Access), and OPC-HDA (Historical Data Access) into one complete specification. The GENESIS automation suite supports these legacy protocols transparently, which incorporates newer communication standards while retaining backwards compatibility.
The Alarms application, which has both client and server components, is an example of a real-time data display where the focus is on alarm and event type data that is specified by the OPC-AE standard. You can configure Alarms to display real time alarm events inside a viewer application that originates on an alarm server application that is monitoring alarm-based OPC-AE devices.
OPC UA is now an IEC standard (IEC 62541) and its specification is split into different parts:
| Title | Description |
|---|---|
| Part 1: Overview and concepts | Presents the concepts and overview of the OPC Unified Architecture (OPC UA). It's useful to understand the remaining parts of the specification. |
| Part 2: Security Model | Describes the OPC UA security model, the security threats of the physical, hardware, and software environments in which OPC UA is expected to run and how OPC UA relies upon other standards for security. |
| Part 3: Address Space Model | Defines the OPC UA address space and its objects with its meta model on which OPC UA information models are based. |
| Part 4: Services | Defines the OPC UA services. The services defined are the collection of abstract RPC (Remote Procedure Calls) that are implemented by OPC UA servers and called by OPC UA clients |
| Part 5: Information Model | Defines the information model of OPC UA. It describes standardized nodes of a server's address space, structure types, and hierarchy. |
| Part 6: Mappings | Specifies the mapping between the security model, the abstract service definitions, the data structures, and the physical network protocols that can be used to implement the OPC UA specification. |
| Part 7: Profiles | Defines the OPC UA profiles that are used to segregate features with regard to testing of OPC UA products and the nature of the testing (tool based or lab based). |
| Part 8: Data Access | Defines the information model associated with data access. |
| Part 9: Alarms and Conditions | Specifies the representation of alarms and conditions in OPC UA. It includes the information model representation of alarms and conditions in the OPC UA address space. |
| Part 10: Programs | Defines the information model associated with programs in OPC UA. |
| Part 11: Historical Access | Defines the information model associated with historical access. |
| Part 12: Discovery and Global Services | Specifies how OPC UA clients and servers interact with discovery servers when used in different scenarios. |
| Part 13: Aggregates | Defines the information model associated with aggregates, used to execute computation for current and historical data. |
| Part 14: Pub/Sub | Defines the OPC UA Pub/Sub (publisher/subscriber) communication model. A publisher is an OPC UA server that exposes an endpoint and this endpoint feeds notifications for subscribers (OPC UA clients). A subscriber is an OPC UA client that is fed by one or more publishers (OPC UA servers). |