OPC Connectivity

inmation collects real-time data following the OPC specification. OPC Technology stands for "Open Platform Communications" and is an approved communication standard for the process industry. It is used to bring real-time data from industrial processes to enterprise systems in the IT-world. OPC uses a Client / Server architecture to transfer data. Each inmation Connector Service has an integrated OPC Client. This is a huge advantage because:

  • It can connect to any OPC Server, then read and collect its data without technical knowledge about the underlying data sources

  • All data is archived in MongoDB, so you can use all functionality of the NoSQL database to work with reliable data generated in the process world

OPC Connectivity Overview
Figure 1. OPC Connectivity Overview

Scalability is part of all OPC architectures: The same client can be connected to multiple OPC Servers at the same time – and vice versa. So a single inmation Connector Service can connect to multiple OPC Servers simultaneously.

The OPC standard is published by the OPC Foundation, which releases the OPC Specifications. The specifications are used to develop OPC applications. Different specifications have been published over time, this is a list of the most used specifications:

  • OPC Data Access (DA) – Real-time Values

  • OPC Historical Data Access (HDA) – Archived Timeline Data

  • OPC Alarms & Events (A&E) – Alarm Messages

  • OPC Security – Address Space Security

  • OPC XmlDA – Web connectivity & OPC in non-Microsoft OS

  • OPC Unified Architecture (UA)

The available OPC Specifications can be broadly split into 2 parts: Classic OPC (OPC DA, A&E, HDA and Security) and Unified Architecture (OPC UA).

Classic OPC specifications are all based on Microsoft DCOM technology, which brings the following implications:

  • Fast, standard-based way to transfer data between Microsoft Windows operating systems.

  • Use of dynamic port range, designed to be used in LAN environments.

  • Windows security / networking needs to be configured (Users / Groups / Active Directory / DCOM Security).

  • Firewall needs to allow random ports

Using DCOM as a technology base implies that classic OPC connections never work well in network architectures outside a LAN environment. This is why OPC Tunneling is used when working with classic OPC in non-LAN networks.

Modern OPC offers more flexible communication:

  • OPC UA uses a service oriented architecture (SOA) to communicate

  • UA can use its own proprietary TCP stack (opc.tcp://), which is especially suitable for high performance industrial data transfer

  • This makes these specifications more suitable to larger OPC architectures, that do require complex routing scenarios

OPC Unified Architecture is the latest generation of OPC technology. OPC XML DA specification is a “hybrid” specification that was developed between Classic and Unified Architecture OPC. It was the first OPC specification to not use DCOM.

The OPC DA XML Datasource client is no longer available in system:inmation. Existing OPC XML-DA datasource objects will now enter an error state when activated. The ability to create new OPC XML DA datasource objects has been retained for reasons of backwards capability but they are non-functional and will also be in an error state.

Further specifications are available and in this article we only describe the most used specifications. For more information on other specifications, visit the OPC Foundation website.